DEPARTMENT OF PHARMACEUTICS FACULTY OF …

Ugwoke Oluchi C.

SOLUPLUS

Digitally Signed by: Content manager’s

DN : CN = Webmaster’s name

O = University of Nigeria, Nsukka

OU = Innovation Centre

Ugwoke Oluchi C.

FACULTY OF PHARMACEUTICAL

DEPARTMENT OF PHARMACEUTICS

SOLID DISPERSIONS BASED ON PEG 4000,

SOLUPLUS® AND THEIR HYBRIDS FOR ENHANCED

DELIVERY OF GLIMEPIRIDE

ACHUAM, JOY NNEJI

PG/M.PHARM/12/62385

i

: Content manager’s Name

Webmaster’s name

a, Nsukka

FACULTY OF PHARMACEUTICAL

DEPARTMENT OF PHARMACEUTICS

SOLID DISPERSIONS BASED ON PEG 4000,

AND THEIR HYBRIDS FOR ENHANCED

ii

SOLID DISPERSIONS BASED ON PEG 4000, SOLUPLUS®

AND THEIR HYBRIDS FOR ENHANCED DELIVERY OF

GLIMEPIRIDE

BY

ACHUAM, JOY NNEJI

PG/M.PHARM/12/62385

DEPARTMENT OF PHARMACEUTICS

FACULTY OF PHARMACEUTICAL SCIENCES

UNIVERSITY OF NIGERIA, NSUKKA

SUPERVISORS: PROF. A. A.ATTAMA

PROF.K. C. OFOKANSI

OCTOBER, 2014

iii

TITLE

SOLID DISPERSIONSBASED ON SOLUPLUS®

, PEG 4000 AND THEIR HYBRIDS

FOR ENHANCED DELIVERY OF GLIMEPIRIDE.

iv

CERTIFICATION

This is to certify that Achuam, Joy Nneji, a postgraduate student in the Department of

Pharmaceutics, with the registration number PG/M.Pharm/12/62385, has satisfactorily

completed the requirements for the award of Master of Pharmacy (M.Pharm) degree in

Physical Pharmaceutics. The work embodied in this project is original and has not been

submitted in part or full for any other diploma or degree of this or any other University.

Supervisor: Prof A. A. Attama Co-supervisor: Prof K. C. Ofokansi

………………………………. …………………………………….

Sign /Date Sign/Date

Head of Department: Prof K.C. Ofokansi

…………………………………………...

Sign/Date

v

DEDICATION

I dedicate this work to God Almighty who is my source and makes all things possible; to my

loving husband and little princess for their love and support during this study; and to my

mum, dad, and siblings for always being there for me. I love you all.

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ACKNOWLEDGEMENT

I ammost thankful to God Almighty for his abundant grace, mercy and guidance to the

successful completion of this study.

I am most grateful and indebted to my supervisor and co-supervisor, Prof A.A. Attama and

Prof K. C. Ofokansi, for their kind and immense assistance throughout the length of this

study, for believing in me more than I do, for always giving a listening ear despite their tight

schedules and workload. May God bless and enlarge your coast.

To my lovely family, my loving husband and pretty angel, whose love and support sustained

me, I say thank you, you are the best. To my parents especially my mum and siblings, I say

thank you for your prayers, assistance, kindness and encouragement. I love you and God

bless you.

My immense thanks go to Dr E.B. Onuigbo, Pharm.F.C. Kenechukwu and Pharm. (Mrs)

A.L.Onugwufor their kind advice, support and guidance through this work. My profound

gratitude goes to all staff of the Department of Pharmaceutics, UNN, especially Prof Ibezim,

Prof.V.C. Okore, Dr. (Mrs) P. O. Nnamani, Dr. M. A.Momoh, Mr Dave Okechukwu, Pharm.

JohnOgbonna, Mr.Chijioke, Mr.F.C.Otuu, Miss Faith, Mrs Chizoba andMr. T. Asogwa for

their encouragement and assistance in one way or the other, God bless you all. To other

Academic staff and non-academic staff of the Faculty, I say a big thank you for all your

contributions.

I appreciate all my friends, colleagues and well wishers who directly or indirectly rendered

some assistance and encouragement, I am most delighted and grateful.

vii

TABLE OF CONTENT

Title ………………..…………………………………………………………………………..i

Certification………………………………………………………………………………...…ii

Dedication.…………………………………………………………………………………....iii

Acknowledgment……………………….………………………………………………….....iv

Table of Content……………………………………………………………………………...v

List of Tables…………………………………………………………………………...……..ix

List of Figures……………………………………………………………………………....... x

Abstract…………………………………………………………………………………...…xiii

CHAPTER ONE

INTRODUCTION………………………………………………………………………....1

1.1 Background of study…………………………….……………………………….….1

1.2 Drug profile of glimepiride ………………………………………………………....2

1.2.1 Definitions …………………………………………………………………… 2

1.2.2 Chemistry of glimepiride …………………………………………………………. 2

1.2.3 Clinical pharmacology ……………………………………………………….……..3

1.2.4 Dosage and administration…………………………………………………………..4

1.2.5 Adverse reactions /side effects………………………………………………………4

1.2.6 Precaution…………………………………………………………………………....5

1.2.7 Drug interactions………………………………………………………………… 5

1.2.8 Uses……………………………………………………………………………… 5

1.3 Solid dispersion…………………………………………………………………… 6

1.3.1 Definition of term……………………………………………………………… 6

1.4 Classification of solid dispersions………………………………………………… 8

1.4.1 Solid state characteristics………………………………………………………… 8

1.4.1.1 Drug and polymer exhibiting immiscibility in fluid state……………………… 8

1.4.1.2 Drug and polymer exhibiting miscibility in fluid state…………………………… 8

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1.4.2 Carriers used for formulation……………………………………………………… 15

1.4.2.1 First generation…………………………………………………………………… 15

1.4.2.2 Second generation…………………………………………………………………. 15

1.4.2.3 Third generation…………………………………………………………………… 18

1.5 Methods adopted in preparation of solid dispersions…………………………… 19

1.5.1 Fusion method…………………………………………………………………….. 19

1.5.2 Solvent evaporation technique…………………………………………………… 20

1.5.2.1 Types of solvent evaporation technique ………………………………………… 21

1.5.3 Supercritical fluid technology……………………………………………………. 22

1.5.4 Solvent melt technique…………………………………………………………… 25

1.5.5 Hot melt extrusion………………………………………………………………… 25

1.5.6 Melt agglomeration process……………………………………………………… 26

1.5.7 Effervescent method…………………………………………………………… 26

1.5.8 Adsorption of insoluble carriers………………………………………………… 27

1.5.9 Co-grinding……………………………………………………………………… 27

1.6 Characterisation of solid dispersions……………………………………………… 27

1.6.1 Physical appearance……………………………………………………………… 28

1.6.2 Percent practical yield…………………………………………………………… 28

1.6.3 Drug content…………………………………………………………………… 28

1.6.4 Aqueous solubility studies…………………………………………………… 28

1.6.5 Dissolution studies……………………………………………………………… 28

1.6.6 Fourier transform infrared (FTIR) spectroscopy………………………………… 29

1.6.7 Thermodynamic methods………………………………………………………… 29

1.6.8 Thermal analysis…………………………………………………………………… 30

1.6.8.1 Thermo-microscopic methods…………………………………………………… 30

1.6.8.2 Differential thermal analysis (DTA)……………………………………………… 30

1.6.8.3 Differential scanning calorimetry(DSC)………………………………………… 30

ix

1.6.9 X-ray diffraction (XRD)…………………………………………………………… 31

1.6.10 Scanning electron microscopy…………………………………………………… 33

1.7 Factors influencing drug release…………………………………………………… 33

1.8 Advantages of solid dispersions…………………………………………………… 33

1.9 Advantages of solid dispersions over other strategies…………………………… 35

1.10 Limitations of solid dispersions…………………………………………………… 36

1.11 Pharmaceutical applications of solid dispersions………………………………… 37

1.12 Commercial solid dispersion products…………………………………………… 38

1.13 Recent advances and future aspects……………………………………………… 46

1.14 Statement of the research problem and justification of study……………………… 48

1.15 Aim of research …………………………………………………….……………….50

1.16 Objectives ofresearch………….…………………………………….……………...50

1.17 Research hypothesis……………………………………………………………….. 51

CHAPTER TWO

MATERIALS AND METHODS…………………………………….………………….. 52

2.1 Materials…………………………………………………………………………… 52

2.1.1 Chemical and reagents…………………………………………………………… 52

2.1.2 Animals……………………………………………………………………………. 52

2.2 Methods…………………………………………………………………………… 53

2.2.1 Identification of glimepiride……………………………………………………...... 53

2.2.2 Preparation of reagents……………………………………………………………. 53

2.2.2.1 Preparation of simulated body fluids………………………………………………..53

2.2.3 Calibration curve of glimepiride…………………………………………………… 54

2.2.4 Preparation of glimepiride solid dispersions……………………………………… 54

2.2.5 Characterisation of solid dispersions……………………………………………… 55

2.2.5.1 Differential scanning calorimetry……………………………………………… 55

2.2.5.2 Fourier transform infrared (FTIR) analysis………………………………… 55

x

2.2.6 Estimation of drug contents………………………………………………………...55

2.2.7 Determination of percentage yield………………………………………………….56

2.2.8 Micromeritic properties of the solid dispersion…………………………………… 56

2.2.9 In vitro drug dissolution……………………………………………………........... 57

2.2.10 Determination of invivoantidiabetic activity…………………………………… 57

2.2.11 Stability studies………………………………………………………………….. 58

2.2.12 Statistical analysis…………………………………………………………… 58

CHAPTER THREE

RESULTS AND DISCUSSION………………………………….………………… 60

3.1 Identification of pure drug sample………………………………………………… 60

3.2 Practical yield of solid dispersions………….……………………………………. 60

3.3 Morphology and physical appearance…………………………………………….. 60

3.4 Drug content…………………………………………………………………….. 68

3.5 Micromeritic properties of the solid dispersions………………………………….. 68

3.6 Invitro drug dissolution studies………………………………………………….. 72

3.7 FTIR spectroscopy …….…………………………………………………………. 79

3.8 Differential Scanning Calorimetry(DSC) ……………………………………….. 81

3.9 Invivoantidiabetic studies………………………………………………………… 98

3.10 Stability studies of the formulations…………………….………………………… 99

CHAPTER FOUR

SUMMARY AND CONCLUSIONS…………………………………………….………. 104

4.1 Summary of results………………………………………………………………… 104

4.2 Conclusions ………………………………………………………...……………....105

4.3 Recommendation……………………………………………………………………105

REFERENCES…………………………………………………………………………….106

APPENDICES…………………………………………….………………………………. 119

xi

LIST OF TABLES

Table 1 Different characterization methods for solid dispersion

Table 2 Commercial solid dispersions products

Table 3 Drugs that has been formulated as solid dispersions

Table 4 Brand of marketed formulation used

Table 5 Different formulations of glimepiride solid dispersions

Table 6 Drug content of the different batches of solid dispersions

Table 7 Micromeritic properties of the different formulations

Table 8 Parameters from the dissolution studies

Table 9 Results of invivo antidiabetic studies

Table 10 Average blood glucose level of the rats for the different groups

Table 11 Results of in vitro dissolution studies in SGF, pH1.2

Table 12 Drug concentration in SIF, pH 7.4

Table 13 Percentage (%) drug concentration in SGF, pH 1.2

Table 14 Percentage (%) drug concentration in SIF, pH 7.4

Table 15 Percentage (%) reduction in initial glycemia

Table 16 Drug content of formulations after a specified period of time

xii

LIST OF FIGURES

Figure 1.0 Structural formula of glimepiride

Figure 2.0 Diagrammatic representation of different formulations and chemical

approaches to enhances solubility

Figure 3.0 Phase diagram of eutectic mixtures

Figure 4.0 Schematic representations of substitutional and interstitial solid solutions

Figure 5.0 Categories of solid dispersions

Figure 6.0 Supercritical region of a hypothetical compound

Figure 7.0 Schematic diagram of the RESS apparatus

Figure 8.0 Photomicrograph of pure drug sample

Figure 9.0 Photomicrograph of PEG 4000

Figure 10.0 Photomicrograph of Soluplus®

Figure 11.0 Photomicrograph of batch S1 formulation

Figure 12.0 Photomicrograph of batch S2 formulation

Figure 13.0 Photomicrograph of batch P1 formulation

Figure 14.0 Photomicrograph of batch P2 formulation

Figure 15.0 Photomicrograph of batch SP1 formulation

Figure 16.0 Photomicrograph of batch SP2 formulation

Figure 17.0 Photomicrograph of batch SP4 formulation

Figure 18.0 Photomicrograph of batch SP5 formulation

Figure 19.0 Bar chart representing the Percentage (%) drug content of the formulations

Figure 20.0 Dissolution profile of glimepiride, its solid dispersions and marketed product

in SIF, pH 7.4

xiii

Figure 21.0 Dissolution profile of glimepiride, its solid dispersions and marketed product

in SGF, pH 7.4

Figure 22.0 Dissolution profile of batch S2 , SP5 and P2 formulations in SIF, pH7.4

Figure 23.0 Dissolution profile of batch S2 , SP5 and P2 formulations in SIF, pH 1.2

Figure 24.0 FTIR spectrum of PEG 4000

Figure 25.0 FTIRspectrum of Soluplus® and Glimepiride

Figure 26.0 FTIR spectrum of Glimepiride

Figure 27.0 FTIRspectrum of Soluplus®

Figure 28.0 FTIR spectrum of batch SP1 formulation

Figure 29.0 FTIR spectrum of batch P1 formulation

Figure 30.0 FTIR spectrum of batch S1 formulation

Figure 31.0 Thermogram of Soluplus®

Figure 32.0 Thermogram of Glimepiride

Figure 33.0 Thermogram of batch S1 formulation

Figure 34.0 Thermogram of PEG 4000

Figure 35.0 Thermogram of batch P1 formulation

Figure 36.0 Thermogram of Soluplus® and PEG 4000 mixture

Figure 37.0 Thermogram of batch SP1 formulation

Figure 38.0 Thermogram of PEG 4000,drug, Soluplus®, physical mixture, batch S1, P1 and SP1 formulations

Figure 39.0 Thermogram of drug, Soluplus®and batch S1 formulation

Figure 40.0 In vivoantidiabetic studies

Figure 41.0 Percentage (%) reduction of initial blood glycaemia

Figure 42.0 Drug content of batches S1, S2, P1, P2, and SP1 formulations at specified periods

xiv

Figure 43.0 Drug content of batches SP2, SP3, SP4, and SP5, formulations at specified periods

Figure 44.0 Beer’s plot of pure Glimepiride

xv

ABSTRACT

The present study investigates the possibility of enhancing the solubility, and hence the

bioavailability of poorly water soluble glimepiride via formation of polyethylene glycol-

polyvinyl caprolactam - polyvinyl acetate grafted copolymer (Soluplus®) and PEG 4000

based solid dispersions by solvent evaporation technique.Different batches of glimepiride

solid dispersions (SD) were prepared using solvent evaporation method with Soluplus®

and

PEG 4000 as polymer matrix at different ratios. The percentage yield, morphology, drug

content, micromeritic properties and drug dissolution studies (in different media: SIF pH 7.4

and SGF 1.2) of the dispersions were evaluated. These formulations were characterized for

solid state properties using differential scanning calorimetry (DSC) and fourier transform

infrared (FTIR) studies. The formulations were further evaluated for alloxan-induced

antidiabetic and stability studies.The different batches formulated showed excellent

morphology, good flow properties, practical yield and drug content. Solid state

characterisation indicated that glimepiride was present in its amorphous form in formulations

with Soluplus® and PEG 4000 due to efficient entrapment in the polymer matrix and with no

drug-polymer interaction. The dissolution rate of all the solid dispersions was found to be

significantly (P < 0.05) more rapid when compared to pure drug in both media except for P2

solid dispersion when compared with the commercial sample in SIF pH 7.4. In the first 30

min, percentage (%)drug released from SDs were 65.83 %, 57.93 %, 58.47 %, 51.45 %,

80.83 %, 81.67 %, 84.02 %, 70.97 %,71.13 % and 46.80 % for batches S1, S2, P1, P2, SP1,

SP2, SP3, SP4, SP5 and Amaryl®

, respectivelyin SIF, pH 7.4. At the end of 120 min, batch SP3

solid dispersion showed maximum % drug released of 96.11 and 57.08 in SIF pH 7.4 and

SGF pH 1.2 respectively, while batch P2 had least % drug released of 74.55 and 40.45 in SIF

pH 7.4 and SGF pH 7.4 respectively. The kinetics of drug release from all the solid

dispersions followed first order. Glimepiride in its pure form had very slow dissolution rate,

xvi

when compared with the solid dispersions. The blood glucose reduction in albino rats by the

solid dispersions was significantly (p < 0.05) more and sustained when compared with the

pure drug sample. The maximum percentage (%) blood glucose reduction of 9.81 % and 8.97

% was achieved in 3 hours for the two groups (A and C, respectively) treated with SDs batch

SP1 and SP3. Thus, the solid dispersions prepared with Soluplus® and polyethylene glycol

4000 might be useful for delivering poorly soluble glimepiride with enhanced solubility and

dissolution rate.

1

CHAPTER ONE

INTRODUCTION

1.1 BACKGROUND OF STUDY

Dissolution is the process by which molecules or ions are transferred from a solid state into

solution. The extent to which the dissolution proceeds under a given set of experimental

conditions is referred to as the solubility of the solute in the solvent. The solubility of a

substance is a measure of the maximum amount of that substance that can be dissolved in a

given amount of solvent to form a stable solution (1). Solubility of drug entity is an intrinsic

factor to its bioavailability and the desired pharmacological activity in the body can only be

achieved when the drug molecules are present in the dissolved state at the site of absorption.

Drug dissolution and release are crucial and limiting step for drug bioavailability particularly

for drugs with low solubility and high permeability.

Many chemical entities are poorly water soluble drugs, not well-absorbed after administration

which can detract from the drugs inherent efficacy. By improving the release profile of these

drugsit is possible to enhance their bioavailability and reduce their side effects.

Dissolution is therefore essential for a drug to be absorbed through the biological membranes

into systemic circulation for therapeutic efficacy(2). Therefore, the improvement of drug

solubility, and hence thereby, its oral bioavailability remains one of the most challenging

aspects of drug development process especially for oral drug delivery system. Many

strategies are involved and have been adopted. Solid dispersions is one of the most effective

means of improving solubility of poorly water soluble drugs.

2

1.2 DRUG PROFILE OF GLIMEPIRIDE

1.2.1 DEFINITIONS

Glimepiride is one of the third generation sulphonyurea , antidiabetic drugs which stimulates

insulin secretion. It is a medium-to-long acting sulfonylurea anti-diabetic drug used in

treatment of Non-Insulin Dependent Diabetes Mellitus (NIDDM). It is very potent and

sometimes classified as second-generation. It is classified under Class II according to

biopharmaceutical classification system. It is a white or almost white powder. The drug

shows low pH dependent solubility. In acidic and neutral aqueous media, glimepiride exhibits

very poor solubility at 37 OC (< 0.004 mg/ml). In a medium pH >7, solubility of the drug is

slightly increased to 0.02 mg/ml. The poor aqueous solubility and slow dissolution rate of the

drug lead to irreproducible clinical response or therapeutic failure in some cases due to low

therapeutic plasma drug levels (3). The compound is soluble in dimethylformamide, soluble

in dichloromethane, slightly soluble in methylene chloride, very slightly soluble in methanol

and practically insoluble in water. This poor solubility may cause poor dissolution and

unpredicted bioavailability. Glimepiride is rapidly absorbed by the liver after oral

administration. It undergoes extensive first pass metabolism in the liver.

1.2.2 CHEMISTRY OF GLIMEPIRIDE

Figure 1.0 Structural Formula

Compendial names: Glimepiride (Ph.Eur., BAN & USAN)

3

Chemical names

a) 1H-Pyrrole-1-carboxamide,3-ethyl-2,5-dihydro-4-methyl-N-[2-[4-[[[[(4

methylcyclohexyl)amino]carbonyl]amino]sulfonyl]phenyl]ethyl]-2-oxo-,trans-;

b) 1-[[p-[2-(3-Ethyl-4-methyl-2-oxo-3-pyrroline-1-carboxamido) ethyl] 3/6phenyl]sulfonyl]-

3-(trans-4-methylcyclohexyl)urea

Molecular formula: C24H34N4O5S

Molecular mass: 490.62

Physical properties

Glimepiride is a white crystalline powder. It is soluble in dimethyl formamide and dimethyl

sulphoxide, dichloromethane, slightly soluble in acetone and very slightly soluble in

methanol, acetonitrile and ethyl acetate. It is insoluble in water and dilute NaOH (pH 12.76)

and slightly soluble in 0.1N HCl (pH 1.24). It has two diastereoisomer forms, cis and trans.

The active substance is the trans form.

1.2.3 CLINICAL PHARMACOLOGY

Glimepiride primarily lowers blood glucose by stimulating the release of insulin

frompancreatic beta cells. Sulfonylureas bind to the sulfonylurea receptor in the

pancreaticbeta-cell plasma membrane, leading to closure of the ATP-sensitive potassium

channel,thereby stimulating the release of insulin. It inhibits gluconeogenesis at hepatic cells

and also increases insulin sensitivity at peripheral target sites.

The drug when administered orally attains peak plasma concentration at approximately 2 – 3

hours. Its duration of action is about 24 hours. It is highly protein bound. Glimepiride is

completely metabolized by oxidative biotransformationafter either an intravenous or oral

dose. The major metabolites are the cyclohexyl-hydroxyl- methyl derivative (Metabolite 1)

and the carboxyl derivative (Metabolite 2). Cytochrome P450 2C9is involved in the

biotransformation of Glimepiride to Metabolite 1. This is further metabolized tocarboxyl

4

derivative by one or several cytosolic enzymes. Metabolite 2 is inactive.Approximately 60 %

of the drug is excreted in the urine and 40% in faeces (as metabolites) with an elimination

half-life of about 5 - 9 hr (4).

1.2.4 DOSAGE AND ADMINISTRATION:

a) Recommended dosing

Glimepiride tablets USP should be administered alone or in fixed dose with Rosiglitazone or

Pioglitazone with breakfast or the first main meal of the day.The recommended starting dose

of glimepiride tablets USP is 1 mg or 2 mg once daily. Patients at increased risk for

hypoglycemia (e.g., the elderly or patients with renal impairment) should be started on 1 mg

once daily.After reaching a daily dose of 2 mg, further dose increases can be made in

increments of 1 mg or 2 mg based upon the patient’s glycemic response. The maximum

recommended dose is 8 mg once daily. Usual maintenance dosage is 1–4 mg once daily. The

maximum initial dosage should not exceed 2 mg once daily. Patients being transferred to

glimepiride tablets USP from longer half-life sulfonylureas (e.g., chlorpropamide) may have

overlapping drug effect for 1 to 2 weeks and should be appropriately monitored for

hypoglycaemia (4).

b) Administration

It is usually administered as a monotherapy, or in combination with other agents like insulin,

metformin, rosiglitazone and pioglitazone (5).

1.2.5 ADVERSE REACTIONS / SIDE EFFECTS OF GLIMEPIRIDE

Vomiting, GI pain, diarrhoea, pruritus, erythema, urticaria, morbilliform, maculopapular

eruptions, leukopenia, agranulocytosis, thrombocytopenia, haemolytic anaemia, aplastic

anaemia and pancytopenia, hyponatraemia, changes in accommodation, blurred vision,

jaundice (6).

5

1.2.6 PRECAUTIONS DURING ADMINISTRATION AND IN PREGNANCY AND

LACTATING MOTHERS

The fasting blood glucose and glycosylated hemoglobin is monitoredevery 3 to 6 months to

determine therapeutic response. Sulphonylureas may cause hypoglycaemia, hypersensitivity

reactions, haemolytic anaemia, etc. It should be used with caution in lactating and pregnant

women (Category C) (7).

1.2.7 DRUG INTERACTIONS OF GLIMEPIRIDE

NSAIDs, salicylates, sulphonamides, chloramphenicol, coumarin, probenecid, CYP2C9

inhibitors fibric acid derivatives, pegvisomant, TCAs, MAOIs and β-adrenergic blockers may

potentiate the hypoglycemic action of glimepiride. Thiazides and other diuretics,

corticosteroids, phenothiazines, thyroid products, oestrogens, oral contraceptives, phenytoin,

nicotinic acid, sympathomimetics, rifampicin, CYP2C9 inducers and isoniazid may reduce

hypoglycemic effect of glimepiride. It may increase the serum levels of ciclosporin. The

serum levels may be increased by fluconazole.It may cause disulfiram-like reaction and

hypoglycemia when used with ethanol and hypoglycemic risk when used with chromium and

garlic (7).

1.2.8 USES

It is used alone or in combination with one or more other oral antidiabetic agents or insulin as

an adjunct to diet and exercise to improve glycemic control in patients with type 2 diabetes

mellitus (8).

6

1.3 SOLID DISPERSION

1.3.1 DEFINITION OF TERM

The term solid dispersion refers to a group of solid products consisting of at least two

different components, a hydrophilic matrix and a hydrophobic drug. The drug can be

dispersed molecularly, in amorphous particles (clusters) or in crystalline particles, while, the

matrix can be either crystalline or amorphous (9). Pharmaceutical polymers are used to create

this matrix and their selection is based on many factors, including physicochemical (e.g.

drug–polymer miscibility and stability) and pharmacokinetic (e.g. rate of absorption)

constraints (10). The solid-dispersion components consist mainly of active pharmaceutical

ingredients (API), the polymer, plasticizers, stabilizers, and other agents.

Chiou and Riegelman defined the term solid dispersion as

“A dispersion involving the formation of eutectic mixtures of drugs with water soluble

carriers by melting of their physical mixtures” (11).

In solid dispersions, a portion of drug dissolves immediately to saturate the gastrointestinal

tract fluid, and excess drug precipitates as fine colloidal particles or oily globules of

submicron size. The development of solid dispersions as a practically viable method to

enhance bioavailability of poorly water-soluble drugs overcame the limitations of previous

approaches such as salt formation, solubilization, cosolvency, and particle size reduction

(11). Solid dispersion is one of the efficient means of improving the dissolution rate and

hence the bioavailability of a range of poorly soluble drugs. Soluplus® and PEG 4000 among

others are typical examples of carriers used in formulation of solid dispersions (12, 13).

7

Figure 2.0 Diagrammatic representation of different formulations and chemical

approaches adopted to enhance solubility or increase the surface area for dissolution

8

1.4 CLASSIFICATION OF SOLID DISPERSIONS

This can be classified based on two terms namely the solid state characteristics and the type

of carriers used for the formulation (14).

1.4.1 SOLID STATE CHARACTERISTICS

1.4.1.1 DRUG AND POLYMER EXHIBITING IMMISCIBILITY IN FLUID STATE

If a drug and polymer are immiscible in their fluid state, it is expected that they would not

exhibit miscibility on solidification of the fluid mixture. Such systems may be regarded as

similar to their corresponding physical mixtures and any enhancement in dissolution

performance may be owing to modification in morphology of drug and/or polymer due to

physical transformation i.e solid to liquid state and back, intimate drug– polymer mixing,

and/or enhanced surface area. Formation of crystalline or amorphous solid dispersions can be

by the rate of solidification of mixture and the rate of crystallization of drug and/or polymer

(15).

1.4.1.2 DRUG AND POLYMER EXHIBITING MISCIBILITY IN FLUID STATE

If the drug and polymer are miscible in their fluid state, then the mixture may or may not

undergo phase separation during solidification, thereby influencing the structure of solid

dispersion (15).

1. EUTECTIC MIXTURES

Eutectic mixtures are formed when the drug and polymer are miscible in their molten state,

but on cooling, they crystallize as two distinct components with negligible miscibility. When

a drug (A) and a carrier (B) are co-melted at their eutectic composition, the melting point of

the mixture is lower than the melting point of either drug or carrier alone. At the eutectic

composition, both drug and carrier exist in finely divided state, which results in higher

surface area and enhanced dissolution rate of drug.

9

Figure 2.3 Phase diagram of Eutetic mixtures (16)

10

2. CRYSTALLINE SOLID DISPERSION

A crystalline solid dispersion (or suspension) is formed when the rate at which drug

crystallizes from drug–polymer miscible mixture is greater than the rate at which drug–

polymer fluid mixture solidifies (15).

3. AMORPHOUS SOLID DISPERSION

In an amorphous solid solution, the solute molecules are dispersed molecularly but irregularly

within the amorphous solvent. If the drug–polymer fluid mixture is cooled at a rate that does

not allow for drug crystallization, then drug is kinetically trapped in its amorphous or a

“solidified-liquid state”.Using griseofulvin in citric acid, Chiou and Riegelman were the first

to report the formation of an amorphous solid solution to improve a drug's dissolution

properties (17). Other carriers, urea and sugars such as sucrose, dextrose and galactose,

organic polymers such as polyvinylpyrrolidone (PVP), polyethylene glycol and various

cellulose derivatives have been utilized for this purpose.

This type of dispersion has the risk or potential for conversion to a more stable and less

soluble crystalline form.

4. SOLID SOLUTION

Solid solution is a solid dispersion that is miscible in its fluid as well as solid state. These

solid solutions may be either of amorphous or crystalline type. In amorphous solid solutions

as the drug is molecularly dispersed in the carrier matrix, its effective surface area is

significantly higher and hence the dissolution rate is increased. Amorphous solid solutions

have improved physical stability of amorphous drugs by inhibiting drug crystallization by

minimizing molecular mobility (18). Crystalline solid solution may result when a crystalline

drug is trapped within a crystalline polymeric carrier.

a) According to extent of miscibility of the two components, solid solutions are of

continuous or discontinuous type.

11

I. Continuous Solid Solutions

In a continuous solidsolution, the components are miscible in allproportions. Theoretically,

this means that thebonding strength between the two components isstronger than the

bonding strength between themolecules of each of the individual components.Solid

solutions of this type have not been reportedin the pharmaceutical literature to date.

II. Discontinuous Solid Solutions

In the case of discontinuous solid solutions, thesolubility of each of the components in the

othercomponent is limited. A typical phase diagram,shows the regions of true solid

solutions. In theseregions, one of the solid components is completelydissolved in the other

solid component. Below acertain temperature, the mutual solubilities of thetwo components

start to decrease.

b) According to the way in which the solvatemolecules are distributed in the solvendum

the twotypes of solid solution are

I) Substitutional Crystalline Solutions

A substitutional crystalline solid dispersion is atype of solid solution which has a

crystallinestructure, in which the solute molecules substitutefor solvent molecules in the

crystal lattice.Substitution is only possible when the size of thesolute molecules differs by

less than 15% or sofrom that of the solvent molecules.

II) Interstitial Crystalline Solid Solutions

In interstitial solid solutions, the dissolvedmolecules occupy the interstitial spaces

betweenthe solvent molecules in the crystal lattice. As inthe case of substitutional

crystalline solid solutions,the relative molecular size is a crucial criterion forclassifying the

solid solution type. In the case ofinterstitial crystalline solid solutions, the solutemolecules

should have a molecular diameter that isno greater than 0.59 A of the solvent

12

molecule'smolecular diameter. Furthermore, the volume ofthe solute molecules should be

less than 20% of thesolvent.

5. Glass Solutions and Glass Suspensions

A glass solution is a homogenous, glassy system in which a solute dissolves in a glassy

solvent. The term glass can be used to describe either a pure chemical or a mixture of

chemicals in a glassy or vitreous state. The glassy or vitreous state is usually obtained by an

abrupt quenching of the melt. It is characterized by transparency & brittleness below the glass

transition temperature.

13

Figure 4.0 Schematicrepresentations of substitutionaland interstitial solid solutions(16).

14

Figure 5.0Categories of solid dispersions (19)

15

1.4.2 CARRIERS USED FOR FORMULATION

1.4.2.1 FIRST GENERATION

First generation solid dispersions were prepared using crystalline carriers such as urea and

sugars, which were the first carriers to be employed in solid dispersion. They have the

disadvantage of forming crystalline solid dispersion, which were thermodynamically more

stable and did not release the drug as quickly as the amorphous ones.

1.4.2.2 SECOND GENERATION

Second generation solid dispersions include amorphous carriers instead of crystalline carriers

which are usually polymers. These polymers include synthetic polymers such as povidone

(PVP), polyethyleneglycols (PEG) and polymethacrylates as well as natural product based

polymers such as hydroxylpropylmethyl-cellulose (HPMC), ethyl cellulose, and

hydroxypropylcellulose or starch derivates like cyclodextrins.

a) POLYETHLENEGLYCOLS (PEG)

Polyethylene glycols, also calledMacrogols® in the Europeanpharmaceutical industry, are

polymers of ethylene oxide, with a molecular weight (MW) usually falling in the range 200 to

300 000 and manufactured by polymerization ofethylene oxide (EO) with water,mono

ethylene glycol or diethyleneglycol as starting material, under alkalinecatalysis (20, 21).

After the desiredmolecular weight is reached (usuallychecked by viscosity measurements

asin-process control) the reaction isterminated by neutralizing the catalystwith acid. Normally

lactic acid is used,but also, acetic acid or others can beused.The result is a very simple

chemicalstructure: HO-[CH2-CH2-O]n-H, where (n)is the number of EO-units.As the MW

increases, so does the viscosity of the PEG. Polyethylene glycols with a meanmolecular

weight up to 400 are non-volatileliquids at room temperature.PEG 600 shows a melting range

of about17 to 22°C, so it may be liquid at roomtemperature but pasty at lowerenvironmental

temperatures. PEGs having800 to 2000 mean molecularweightare pasty materials with a

16

lowmelting range. Above a molecular weightof 3000, the polyethylene glycols aresolids and

are available not only in flakedform but also as powder. Polyethylene glycols upto a

molecular weight of 35,000 arecommercially available. The hardness ofpolyethylene glycols

increases with increasingmolecular weight, however the meltingrange goes up to a maximum

value ofabout 60°C (22).

The most important property of allPEGs is their solubility in water, whichmakes them ideally

suitable for use incountless different applications. LiquidPEGs up to PEG 600 are miscible

withwater in any ratio. But even solid PEGgrades have excellent solubility in water.Although

it falls slightly with increasingmolar mass, even 50% (w/w) of PEG

35,000 can be dissolved at roomtemperature in water. The solubility andthe viscosity of the

solutions are notaffected by the presence of electrolytes,since PEGs are non-ionic substances.

PEGsare quite soluble in hard water or in otheraqueous solutions of various salts.

Some substances react with PEGs byforming precipitates;these include, phenol,cresol,

resorcinol, salicylic acid, tannin,potassium iodide, tetraiodo-bismutic acidor mercury chloride

beside others. Someof those reactions can be used forqualitative detection or

quantitativeanalysis of polyethylene glycols.For the manufacture of solid dispersions and

solutions, PEGs with molecular weights of 1500 to 20 000 are usually employed, but PEGs of

4000 to 6000 are most frequently used because in this MW range the water solubility is still

very high, but hygroscopy is not a problem and the melting points are already over 50oC.

Their solubility in water is generally good, but decreases with MW. A particular advantage of

PEGs for the formation of solid dispersions is that they also have good solubility in many

organic solvents. The melting point of the PEGs of interest lies under 65 oC in every case

(e.g. the melting point of PEG 1000 is 30 to 40 oC, the melting point of PEG 4000 is 50 to

58oC and the melting point of PEG 20 000 is 60 to 63oC (23). Additional attractive features

17

of the PEGs include their ability to solubilise some compounds and also to improve

compound wettability (24).

If a PEG with too low a MW is used, this can lead to a product with a sticky consistency that

is difficult to formulate into a pharmaceutically acceptable product (25). PEGs with higher

MW have also been used with success: products containing PEG 8000 and 10 000 showed

enhanced dissolution rates compared to the pure drug(26, 27).

The drug/carrier ratio in a solid dispersion is one of the main influences on the performance

of a solid dispersion. If the percentage of the drug is too high, it will form small crystals

within the dispersion rather than remaining molecularly dispersed. On the other hand, if the

percentage of the carrier is very high, this can lead to the complete absence of crystallinity of

the drug and thereby enormous increases in the solubility and release rate of the drug. Lin and

Cham (28) showed that solid dispersions of naproxen in PEG 6000 released drug faster when

a 5 or 10% naproxen loading was used than when a 20, 30 or 50% loading was used. These

results could be explained on the basis of X-ray diffraction results, which indicated that

dispersions with low loading levels of naproxen were amorphous whereas those with high

loadings were partly crystalline. However, the upper limit to the percentage carrier that can

be employed is governed by the ability to subsequently formulate the solid dispersion into a

dosage form of administrable size.

Griseofulvin is probably the most studied drug with respect to dispersion in PEGs. Chiou and

Riegelman were able to achieve a noticeable increase in the release rate of griseofulvin from

solid dispersions in PEG 4000, 6000 and 20 000 (17). The fruit of research with PEG/

griseofulvin combinations is the marketed product, Gris-PEG. More recent studies with

griseofulvin and PEGs have focussed on mixtures with various emulsifying agents. An

increase in the release rate by formulation as a solid dispersion in PEG 4000 has been

observed for many drugs, including oxazepam (29, 30), piroxicam (31)and zolpidem (32).

18

Other drugs which exhibit elevated release rates when formulated as PEG solid dispersions

include Sr33557, a new calcium antagonist (33), ketoprofen (34), oxazepam , nifedipine (35),

phenytoin (36), ursodeoxycholic acid (37), fenofibrate (38) and prednisolone (39).

1.4.2.3 THIRD GENERATION

Recently, it has been shown that the dissolution profile can be improved if the carrier has

surface activity or self emulsifying properties. Therefore, third generation solid dispersions

appeared. The use of surfactant such as Inulin, Inutec SP1, Compritol 888 ATO, Gelucire

44/14 and Poloxamer 407 as carriers was shown to be effective in originating high

polymorphic purity and enhanced in vivo bioavailability (40).

a) SOLUPLUS®

Soluplus®

is a polymeric solubilizer with an amphiphilic chemical structure which was

particularly developed for solid solutions. Due to its bifunctional characteristics, it is able to

act as a matrix polymer for solid solutions as well as being capable of solubilising poorly

soluble drugs in aqueous media. It can also increase bioavailability of poorly soluble drugs.

Soluplus® is a polyvinyl caprolactam-polyvinyl acetate polyethylene glycol co-polymer. It is

a free flowing white to slightly yellowish granules with a faint characteristic odour. It has an

average molecular weight of 90000-140000 g/mol. Its critical micelle concentration and glass

transition temperature are 7.6 mg/l and approximately 70 oC respectively. It is soluble in

water, acetone (up to 50%), methanol (up to 45%), ethanol (up to 25%) and

dimethylformamide (up to 50%). A high polymer concentration may result in a cloudy or

turbid aqueous solution due to the formation of colloidal Soluplus®

micelles. This

phenomenon is more pronounced at elevated temperature (approximately 40oC), which is a

lower critical solution temperature (LCST). Thus, when the polymer solution is heated at or

above its LCST, a clear polymer solution turns cloudy due to formation of larger micelles but

this reverses upon cooling (41).

19

1.5 METHODS ADOPTED IN PREPARATION OF SOLID DISPERSIONS

The core steps involved in the formation of solid dispersion between a drug and polymer

include

• Transforming drug and polymer from their solid state to fluid or fluid-like state

through processes such as melting, dissolving in solvent or cosolvent, or subliming.

• Mixing the components in their fluid state.

• Transforming the fluid mixture into solid phase through processes such as congealing,

solvent removal, and condensation of sublimed mixture (42).

Basically, there are two methods of preparing solid dispersions, fusion and solvent processes.

In case of thermolabile drugs or those with high melting points, a modified method is

employed known as melting solvent method. The latter method is limited to drugs with low

therapeutic doses, i.e. below 50 mg (43).

However, for the preparation of solid dispersions, several methods have been reported in

literature, which are described as follows:

1.5.1 FUSION METHOD

In this method, the carrier is heated to a temperature just above its melting point and drug is

incorporated into the matrix. If the drug has high solubility in the carrier, the drug could

remain “dissolved” in the solid state, yielding a solid solution. The melt is solidified in an ice

bath under rigorous stirring, pulverized and then sieved. Rapid congealing is desirable,

because it results in supersaturation of drug as a consequence of entrapment of soluble

molecule in the solvent matrix by instantaneous solidification. The first solid dispersions

created for pharmaceutical applications were prepared by the fusion method. The dispersion

consisted of sulfathiazole and urea as a matrix (44).

20

Advantages

• It is a more convenient and economical method for drugs stable at temperatures

below 100 oC

• Technically, it is an easier method if the drug and carrier are miscible in the molten

state.

• It precludes the use an organic solvent.

• Dissolution for dispersions obtained by melting technique are much faster than those

prepared using solvent techniques (45).

Drawbacks

• High melting carrier cannot be used

• Thermal degradation or instability may result at the melting point

• Decomposition may take place, often dependent upon composition, fusion time and

rate of cooling

• Evaporation or sublimation and polymeric transformation of the dispersion

component may take place

• Solidified melt may be tacky and difficult to handle.

• Immiscibility between drug and carrier results in irregular crystallization that causes

obvious problems during formulation (46, 47)

1.5.2 SOLVENT EVAPORATION TECHNIQUE

This technique involves dissolving the drug and the carrier in a suitable organic solvent or

acombination of solvents to get a clear solution. As the solvent is being removed,

supersaturation occurs followed by simultaneous precipitation of the constituents resulting in

a solid residue. The solvent is then evaporated directly on a water bath or hot plate or using a

rota-vapour. The resulting solid dispersion is stored in the desiccator under vaccum and

pulverized to obtain the desired size fraction. The important prerequisite for the

21

manufacturing of solid dispersion using the solvent method is that both drug and the carriers

are sufficiently soluble in the solvent (48).

Advantages of solvent evaporation technique

• High melting carries can also be utilized

• Thermal decomposition of drug and carriers associated with the fusion method can be

avoided

Drawbacks of solvent evaporation technique

• Larger volumes of organic solvent have to be used which makes the process slightly

expensive

• Residual solvent can have possible adverse effect

• Supersaturation of the solute cannot be attained unless the system goes through a

highly viscous phase

• Selection of common solvent is difficult

• Drug particle size is affected by temperature and rate of evaporation (49).

1.5.2.1 TYPES OF SOLVENT EVAPORATION TECHNIQUE

The choice of solvent and its removal rate are critical to the quality of the dispersion.

Depending upon the method of evaporation, there are various types of techniques.

I. Spray drying

Manufacture of milk powder was one of the first applications of spray drying when the

method was developed in 1920. This method consists of dissolving or suspending the drug

and carrier, then spraying it into a stream of heated air to remove the solvent. Spray drying

usually yields drug in the amorphous state, however sometimes the drug may be (partially)

crystallized during processing(50, 51).

22

Advantages of spray drying

• Ability to work with temperature sensitive APIs.

• Tremendous formulation flexibility from the wide variety of solvents, polymers and

adjuvants that can be employed.

• Enhancement in performance that can be obtained by mixing the API and polymer at

the molecular level in solution and then freezing this morphology in place through

rapid solvent removal.

Drawbacks of spray drying

• Added costs associated with the use and consumption of the organic solvents.

• Requirement of unit operation for residual solvent removal.

II. Freeze drying

To overcome the disadvantages of the earlier discussed techniques and to obtain a much

faster dissolution rate, freeze drying technique has been proposed. The drug and the carrier

are dissolved in a common solvent, which is immersed in liquid nitrogen until it is fully

frozen; then the frozen solution is further lyophilized. The instance includes that a solid

dispersion of tenoxicam with skimmed milk, prepared using freeze drying showed 23-fold

increase in solubility with respect to the plain drug (52).

Advantages of freeze drying

• Risk of phase separation is minimized as soon as the solution is vitrified.

• Offers the potential to customize the size of the particles to make them suitable for

further processing.

Drawbacks of freeze drying

• The manufacturing process is very expensive.

• The technique is not suitable for all the products (52).

1.5.3 SUPERCRITICAL FLUID TECHNOLOGY (SCF)

A Super Critical Fluid is asubstance that exists above its critical point, whichis defined by

the conditions of temperature andpressure at which liquid and gaseous states of asubstance

23

coexist. When a liquid is heated, its density continues to decrease, while the density of vapor

being formed continues to increase. At the critical point, densities of liquid and gas are equal

and there is no phase boundary, see Figs 6.0 and 7.0. Above the critical point, the fluid

possesses the penetrating power typical of a gas and the solvent power typical of a liquid.

Supercritical fluid methods are mostly applied with carbon dioxide (CO2), which is used as

either a solvent for drug and matrix or as an antisolvent. When supercritical CO2 is used as

solvent, matrix and drug are dissolved and sprayed through a nozzle, into an expansion vessel

with lower pressure and particles are immediately formed. The adiabatic expansion of the

mixture results in rapid cooling. This technique does not require the use of organic solvents

and since CO2 is considered environmentally friendly, this technique is referred to as ‘solvent

free’. The technique is known as Rapid Expansion of Supercritical Solution (RESS).

However, the application of this technique is verylimited, because the solubility in CO2 of

most pharmaceutical compounds is very low (<0.01wt-%) and decreases with increasing

polarity.

(53).

Advantages of SCF

• Dissolving power of the SCF is controlled by pressure and/or temperature

• SCF is easily recoverable from the extract due to its volatility

• Non-toxic solvents leave no harmful residue

• High boiling components are extracted at relatively low temperatures

• Thermally labile compounds can be extracted with minimal damage as low

temperatures can be employed by the extraction

• Non-inflammable and inexpensive technique

Drawbacks of SCF

• Elevated pressure required

• Compression of solvent requires elaborate recycling measures to reduce energy costs

• High capital investment for equipment.

24

Figure 6.0Supercritical region of a hypothetical compound (Indicated by the dotted lines), (16)

Figure 7.0 Schematicdiagramof the RESS apparatus used in supercritical fluid technology (16)

25

1.5.4 SOLVENT MELT TECHNIQUE

To overcome the problems associated with fusion technique, a blend of fusion and solvent

evaporation method has also been proposed. In this technique, the drug is dissolved in an

organic solvent and mixed with the melted carrier. The solvent is then evaporated and the

resultant product is pulverized to the desired size (54).

Advantages of solvent melt technique

• Possesses unique advantages of both the fusion and solvent evaporation methods

• Useful for thermolabile drugs with high melting point.

Drawbacks of solvent melt technique

• Technique is limited to drugs with a low therapeutic dose (less than 50 mg)

1.5.5 HOT MELT EXTRUSION

Hot melt extrusion approach represents the advantageous means of preparation of solid

dispersions by using the twin screw hot melt extruder where only thermostable components

are relevant. The extruder consists of a hopper, barrel, a die, a kneading screw and heaters.

The physical mixture is introduced into the hopper that is forwarded by feed screw and

finally is extruded from the die. The effect of screw revolution speed and water content on

preparation of solid dispersions should be investigated, since these parameters have profound

impact on the quality of solid dispersions. To reduce the melt viscosity in the extrudate and to

be able to decrease temperature settings, a plasticizer can be added to the formulation.

Typically, a conventional plasticizer such as triacetin or polyethylene glycol that lowers the

processing temperature is used in concentration range of 5-30 % weight of the extrudate.

Carbon dioxide can act as a temporary plasticizer. During extrusion, carbon dioxide is

transformed to gaseous phase. As a consequence, carbon dioxide escapes from the extrudate

and does not appear in final product. The role of methylparaben and sorbitol has also been

investigated as plasticizer in preparation of sold dispersions by the extrusion method (55).

26

Advantages of hot melt extrusion

• Possibility of continuous production makes it suitable for large scale production.

• The product is easier to handle because at the outlet of the extruder, the shape can be

adapted to the next processing step without grinding(55).

Drawbacks of hot melt extrusion

• High energy input requires shear forces and high temperature.

• design of screw assemblies and extruder dies, have significant impact on degradation

of drugs and excipients

1.5.6 MELT AGGLOMERATION PROCESS

This technique has been used to prepare solid dispersion where the binder acts as a carrier. In

addition, solid dispersions are prepared either by heating binder, drug and excipients to a

temperature above the melting point of the binder (melt-in procedure) or by spraying a

dispersion of drug in molten binder on the heated excipients (spray-on procedure) by using a

high shear mixer. The effect of binder type, method of manufacturing and particle size are

critical parameters in preparation of solid dispersions by melt agglomeration.

1.5.7 EFFERVESCENT METHOD

Effervescent solid dispersions incorporate sodium bicarbonate and organic acids (citric,

tartaric or succinic), which react with each other to yield an effervescent mixture. By

combining poorly soluble drugs with organic acids, one should obtain an effervescent solid

dispersion, which may increase the dissolution and absorption rates of poorly soluble drugs.

Citric acid/sodium bicarbonate was found to be the most effective carrier for releasing

prednisone and primidone and sodium bicarbonate/succinic acid was observed to be the best

carrier for griseofulvin. Such dispersion can be made by fusion technique as explained above

(16).

1.5.8 ADSORPTION ON INSOLUBLE CARRIERS

27

These dispersions are also referred to as surface solid dispersions. In this method, the support

material is suspended in a solution of the drug followed by evaporation of the solvent. The

resulting material contains the drug in a “molecularly micronized” state on the surface of the

carrier. Here, adsorbents maintain the concentration gradient (Cs-Ct) to its maximum, thus

increasing the dissolution rate. A special technique under these methods isthe fluidized bed

system. It involves first preparation of spraying solution by dissolving bothdrug and carrier

and then sugar spheres are charged to fluidized bed granulator and coated.

These spheres are fluidized by spraying solution and the coated pellets are dried. Solid

dispersion of poorly water-soluble drug nifedipine was prepared in

hydroxypropylmethylcellulose (HPMC) on sugar spheres using this technique (16).

1.5.9 CO-GRINDING

In this method, accurately weighed drug powder and the carrier are mixed for some time

using a blender at a specified speed. The mixture is then charged into the chamber of a

vibration ball mill for grinding (56).

1.6 CHARACTERISATION OF SOLID DISPERSIONS

A number of techniques can be employed to identify the physical nature of the solid

dispersions. No single method however, can furnish the complete information and hence a

rational combination of the methods is preferred. Themost important methods that can be

used to characterize solid dispersions are thermo-analytical, X-raydiffraction, infrared

spectroscopy and measurement of therelease rate of the drug. In addition to characterizing

thesolid dispersion, these methods can be used to differentiatebetween solid solutions

(molecularly dispersed drug), soliddispersions in which drug is only partly

molecularlydispersed and physical mixtures of drug and carrier. Dueto the complex

composition of these preparations, it is often difficult to delineate precisely between

molecularlydispersed and non-molecularly dispersed systems and differentanalytical methods

28

may yield disparate results. It isusually assumed that dispersions in which no crystallinitycan

be detected are molecularly dispersed and the absenceof crystallinity is used as a criterion to

differentiate betweensolid solutions and solid dispersions.

1.6.1 PHYSICAL APPEARANCE

This includes a visual inspection of the solid dispersions formulated.

1.6.2 PERCENT PRACTICAL YIELD

Percentage practical yield is calculated to know about percent yield or efficiency of any

method.Thus, it helps in selection of appropriate method of production. SDs were collected

and weighed todetermine practical yield (PY) from the following equation (57)

PY (%) = [Practical Mass (Solid dispersion) /Theoretical Mass (Drug+ Carrier) ×100

1.6.3 DRUG CONTENT

In this method, definite amount of solid dispersionis taken and dissolved in a suitable solvent

in whichdrug is freely soluble, then after appropriatedilution, concentrations are measured by

UVSpectrophotometry (58).

1.6.4 AQUEOUS SOLUBILITY STUDIES

These are carried out to determine the solubility of drugalone in aqueous medium and also in

the presence ofcarriers .This is done by dissolving excess drugin different flasks containing

differentconcentrations of carrier in distilled water. Theflasks are shaken thoroughly for 6 h

and keptaside for 24 h .The suspensions are filtered ,diluted suitably and their absorbance

measured atsuitable wavelength (59).

1.6.5 DISSOLUTION STUDIES

Dissolution studies are the most significantevaluation parameter for any solid dosage form.

The method involves measuring thein vitrodissolution rates of the eutectic mixtures, glass or

solid solutions as against the pure drug. This is usually carried out using several methods in

the literature (60). It tellswhether the solid dispersion has improved thedissolution rate or

29

not. In other words, dissolution study is carried out to determine therate and extent of

dissolution. The degree of crystallinity can also be studied if it is carried out under standard

conditions. Release rate experiments cannot be used on a stand-alonebasis to determine

whether a solid solution has been formedor not. However, in conjunction with other

physicochemicaldata, they provide strong evidence for the formation of amolecularly

dispersed or nearly molecularly dispersedsystem. When the goal of preparing a solid

dispersion is to improve the dissolution characteristics of the drug inquestion, the results of

the release rate experiments areobviously of prime importance in assessing the success ofthe

approach. A well-designed release experiment will showwhether the solubility of the drug

and its dissolution rate hasbeen enhanced, and also whether the resulting

supersaturatedsolution is stable or tends to precipitate quickly.Comparison of results with

those for pure drug powderand physical mixtures of the drug and carrier can help toindicate

the mechanism by which the carrier improvesdissolution: via solubilisation and wetting

effects whichcould be affected by a simple mixture of the components,or by formation of a

solid dispersion/solution (61).

1.6.6 FOURIER TRANSFORM INFRARED (FTIR) SPECTROSCOPY

FT-IR spectroscopy is used to study the possibility of an interaction between drug and

polymer in solidstate. It involves the use of potassium bromideand Infra red

spectrophotometer. It can be used todetect the variation in the energy distribution of

interactions between drug and matrix (62, 63).

1.6.7 THERMODYNAMIC METHODS

In this analysis, the phase diagrams of eutectic and solid solution systems give the value of

heats of fusion, entropies and partial pressures at various compositions that helps to

determine the solubility gap below the solid-liquid equilibrium temperature (64).

30

1.6.8 THERMAL ANALYSIS

1.6.8.1 THERMO-MICROSCOPIC METHODS

This is a visual method of analysis using a polarized microscope with a hot stage to determine

the thawand melting points of solids. The method is advantageous as small amount of sample

is requiredand direct observation of the changes taking place in the sample through the thaw

and melt stages can be made. Thetechnique has been used to support DTA or DSC

measurement. It gives information about the phasediagram of binary systems (65).

1.6.8.2 DIFFERENTIAL THERMAL ANALYSIS (DTA)

This is an effective thermal method for studying the phase equilibria of pure substance or

solid mixture.Differential heat changes that accompany physical and chemical changes are

recorded as a function oftemperature as the substance is heated at uniform rate. In addition to

thawing and melting, polymorphic transition, evaporation, sublimation, desolvation and other

types of changes such asdecomposition of the sample can be detected. The method has been

used routinely to identify differenttypes of solid dispersion. A sample size of less than 1 mg

can be used (65).

1.6.8.3 DIFFERENTIAL SCANNING CALORIMETRY

Thermoanalytical methods include all methods that examine acharacteristic of the system as a

function of temperature.Of these, differential scanning calorimetry (DSC) is themost highly

regarded method. DSC enables the quantitativedetection of all processes in which energy is

required orproduced (i.e. endothermic and exothermic phase transformations).The usual

method of measurement is to heat thereference and test samples in such a way that the

temperatureof the two is kept identical. If an energy-requiring phasetransition occurs in the

test sample, extra heat is applied tothis sample so that its temperature climbs at the same rate

asin the reference. The additional heat required is recordedand used to quantitate the energy

31

of the phase transition.Exothermic transitions, such as conversion of one polymorphto a more

stable polymorph, can also be detected.Lack of a melting peak in the DSC of a solid

dispersionindicates that the drug is present in an amorphous ratherthan a crystalline form.

Since the method is quantitative innature, the degree of crystallinity can also be calculated

forsystems in which the drug is partly amorphous and partlycrystalline. However,

crystallinities of less than 2% cannotgenerally be detected with DSC (66).

1.6.9 X-RAY DIFFRACTION (XRD)

In this analytical tool, intensity of x-ray reflection ismeasured which is a function of

diffraction method.The diffraction method is very important andefficient tool in studying the

physical nature of soliddispersion which has been used in crystal structurestudies in two

different ways.

• Single crystal x-ray crystallography dealingwith the determination of bond angle and

interatomic distances.

• Power x-ray diffraction dealing with the study of crystal lattice parameter, where the

x-ray diffraction intensity from a sample is measured as a function of diffraction

angles. Thus, changes in diffraction pattern indicate changes in crystal structure.

The relationship between wavelength of the x-ray, the angle of diffraction, θ, and the distance

between each set of atomic planes of crystal lattice, d, is given by equation: Mλ=2d sin θ,

where M represents the order of diffraction (64,65).

32

Table 1.0 Different characterisation methods for solid dispersions

S. No Characterization Methods Significance

1 Drug-carrier miscibility Hot stage microscopy (HSM) Differential scanning calorimeter (DSC) X-ray Diffraction (XRD) Nuclear magnetic resonance (NMR)

To find out the complex formation between drug and carrier. To check the degree of amorphization.

2 Drug-carrier interactions

Fourier transform infrared spectroscopy (FTIR) Raman spectroscopy Solid state NMR studies

To find out the solid state interaction between drug and carrier and formation of inclusion complex.

3 Surface properties Dynamic vapour sorption Inverse gas chromatography Atomic force microscopy Raman microscopy

To study the morphology and degree of crystallinity.

4 Stability Humidity studies Isothermal calorimeter DSC (Tg, temperature recrystallisation) Dynamic vapour sorption Saturated solubility studies

To find out the degree of recrystallization.

5 Amorphous content Polarized light optical microscopy Hot stage microscopy Humidity stage microscopy DSC (MTDSC) Powder XRD

To find out the amorphous transition.

6 Dissolution rate Dissolution studies Intrinsic dissolution Dynamic solubility studies

To find out the rate and extent of drug release (55).

33

1.6.10 SCANNING ELECTRON MICROSCOPY

Scanning electron microscopy gives the primary information of morphological and surface

characteristics of the solid dispersions.

1.7 FACTORS INFLUENCING DRUG RELEASE

• Nature of carriers

• Drug-\\ carrier ratio

• Method of preparation

• Cooling conditions

• Synergistic effect of two carriers used

• Influence of carrier chain length/molecular weight (67-69)

1.8 ADVANTAGES OF SOLID DISPERSION

Solid dispersion as a technique used to enhance drug bioavailability has the following

advantages:

I Particles with reduced particle size and increased dissolution rate

Molecular dispersions, as solid dispersions, represent the last state on particle size reduction,

and after carrier dissolution, the drug is molecularly dispersed in the dissolution medium.

Solid dispersions apply this principle to drug release by creating a mixture of a poorly water

soluble drug and highly soluble carriers. A high surface area is formed, resulting in an

increased dissolution rate and, consequently, improved bioavailability.

Solubility and permeability are the main factors that control oral bioavailability of a drug

substance. Generally, when the drug solubility in water is less than 10 mg/ml, dissolution is

the rate-limiting step in the process of drug absorption (70).

As described by the Noyes-Whitney’s equation, dissolution rate can be increased through

some factors including increasing the surface area, and this can be achieved through reducing

the particle size. Different methods have been used to reduce the particle size, such as

micronization, recrystallization, freeze drying and spray drying. Micronization of poorly

soluble drugs by milling has been used for many years in the pharmaceutical industry in order

34

to enhance the dissolution rate of those drugs. However, fine particles may not always

produce the expected faster dissolution. This primarily results from the aggregation and

agglomeration of fine particles. In addition, poor wettability of fine powders may reduce the

dissolution rate. Solid dispersion techniques have been used to enhance the dissolution rate of

many poorly water soluble drugs. Particle size reduction and reduced agglomeration would

both increase the exposed surface area of the drug. When solid solutions or amorphous

precipitations are formed, particle size of the active ingredient is reduced to the minimum

level. In addition, the carrier material may contribute to increasing the dissolution rate

through its solubilising and wettability-enhancing properties (71).

II Particles with improved wettability

A strong contribution to the enhancement of drug solubility is related to the drug wettability

improvement verified in solid dispersions. It was observed that even carriers without any

surface activity, such as urea improved drug wettability. Carriers with surface activity, such

as cholic acid and bile salts, when used, can significantly increase the wettability properties

of drugs. Moreover, carriers can influence the drug dissolution profile by direct dissolution or

co-solvent effects. Recently, the inclusion of surfactants in the third generation solid

dispersions reinforced the importance of this property (73).

III Particles with higher porosity

Particles in solid dispersions have been found to have a higher degree of porosity. The

increase in porosity also depends on the carrier properties, for instance, solid dispersions

containing linear polymers produce largerand more porous particles than those containing

reticular polymers and, therefore, result in a higher dissolution rate. The increased porosity of

solid dispersion particles also hastens the drug release profile (72).

35

IV Drugs in amorphous state

Drugs that are in crystalline form and poorly water soluble, when in the amorphous state tend

to have higher solubility. The enhancement of drug release can usually be achieved using the

drug in its amorphous state, because no energy is required to break up the crystal lattice

during the dissolution process. In solid dispersions, drugs are presented as supersaturated

solutions after system dissolution, and it is speculated that, if drugs precipitate, it is as a

metastable polymorphic form with higher solubility than the most stable crystal form (72).

1.9 ADVANTAGES OF SOLID DISPERSIONS OVER OTHER STRATEGIES TO

IMPROVE BIOAVAILABILITY OF POORLY WATER SOLUBLE DRUGS

Improving drug bioavailability by changing their water solubility has been possible by

chemical or formulation approaches. Chemical approaches to improving bioavailability

without changing the active target can be achieved by salt formation or by incorporating polar

or ionizable groups in the main drug structure, resulting in the formation of a pro-drug. Solid

dispersions appear to be a better approach to improve drug solubility thanthese techniques,

because they are easier to produce and more applicable. For instance, salt formation can only

be used for weakly acidic or basic drugs and not for neutral drugs. Furthermore, it is common

that salt formation does not achieve better bioavailability because of its in-vivo conversion

into acidic or basic forms (72). Moreover, these types of approaches have the major

disadvantage that the sponsoring company is obliged to perform clinical trials on these forms,

since the product represents a new chemical entity. Formulationapproaches include

solubilization and particle size reduction techniques, and solid dispersions, among others.

Solid dispersions are more acceptable to patients than solubilization products, since they give

rise to solid oral dosage forms instead of liquid as solubilization products usually do. Milling

or micronization for particle size reduction is commonly performed as an approach to

improve solubility, on the basis of the increase in surface area. Solid dispersions are more

36

efficient than these particle size reduction techniques, since the latter have a particle size

reduction limit which frequently is not enough to improve considerably the drug solubility or

drug release in the small intestine and, consequently, to improve the bioavailability.

Moreover, solid powders with such a low particle size have poor mechanical properties, such

as low flow and high adhesion, and are extremely difficult to handle.

1.10 LIMITATIONS OFSOLID DISPERSION

Despite extensive expertise with solid dispersions, they are not broadly used in commercial

products, mainly because there is the possibility that during processing (mechanical stress) or

storage (temperature and humidity stress), the amorphous state may undergo crystallization.

The effect of moisture on the storage stability of amorphous pharmaceuticals is also a

significant concern, because it may increase drug mobility and promote drug crystallization.

Moreover, most of the polymers used in solid dispersions can absorb moisture, which may

result in phase separation, crystal growth or conversion from the amorphous to the crystalline

state or from a metastable crystalline form to a more stable structure during storage. This may

result in decreased solubility and dissolution rate. Therefore, exploitation of the full potential

of amorphous solids requires their stabilization in solid state, as well as during in-

vivoperformance. The limitations of this technology have been a drawback for the

commercialization of solid dispersions(73-75).

The limitations include

• Laborious and expensive methods of preparation,

• Non-reproducibility of physicochemical characteristics,

• Difficulty in incorporating into formulation of dosage forms,

• Scale-up of manufacturing process, and

• Instability of the drug and vehicle(75)

37

1.11 PHARMACEUTICAL APPLICATIONS OF SOLID DISPERSIONS

Solid dispersion systems have been applied in the following as a contribution towards

improving drug therapy.

• In improving immunosuppressive therapy in lung transplant patients, dry powder

formulation consisting of a solid dispersion (e.g. Cyclosporine A) for inhalation is

prepared. It can avoid many problems like use of local anaesthesia and irritating

solvents.

• Solid dispersion formulations were demonstrated to accelerate the onset of action for

drugs such as nonsteroidal anti-inflammatory drugs (NSAIDS) where immediacy of

action is crucial in relieving acute pain and inflammation.

• Solid dispersion systems were shown to provide bioavailable oral dosage forms for

anti-cancer drugs, which could be substituted for standard injections to improve

patient comfort and compliance.

• Solid dispersion systems were also found to reduce food effect on drug absorption,

thus increasing the convenience of drug therapy as the need for some drugs to be

taken with food was eliminated.

• Solid dispersion- based dosage form allowed for greater drug loading per dose and

improved stability over a soft gelatin capsule formulation, which thereby improved

the convenience of drug therapy by reducing the dosing regime and eliminating the

need for refrigerated storage.

• Improved absorption efficiency demonstrated for solid dispersion systems allows for

a reduction in the content of active agent per dose, thus decreasing the cost associated

with these drug therapies.

38

• It also acts as a functional carrier that offers the added benefit of targeting the release

of highly soluble forms of poorly water soluble drugs to an optimum site of action

(76-79).

1.12 COMMERCIAL SOLID DISPERSION PRODUCTS

In spite of several years of research on solid dispersions, their commercial application is

limited. Only a few products have been marketed so far (80-82).Amongst these few are those

mentioned in Table 2. Furthermore, different research work has been carried on solid

dispersions with the goal of enhancing the delivery of poorly water soluble drugs using

various methods of formulation and different types of carriers/polymers. Some of these have

been listed in Table 3.

39

Table 2.0 Commercial solid dispersions products

Commercial products Polymer used Manufacturer

Company Gris-PEG® (Griseofulvin)

Polyvinylpyrrolidone (PVP)

VIP Pharma

Intelence® (Etravirine) Hypromellose, and microcrystalline cellulose

Tibotec, Yardley, PA

Cesamet® (Nabilone) Polyvinylpyrrolidone (PVP)

Valeant Pharmaceuticals, Costa Mesa, CA

Sporanox® (Itraconazole)

Hydroxypropylmethyl cellulose (HPMC)

Janssen Pharmaceutica, Titusville, NJ

lopinavir and ritonavir Polyvinylpyrrolidone–vinyl acetate copolymer

Abbott Laboratories, Abbott Park, IL (60)

40

S/No Drug used Polymer and method used Consequence

1

Griseofulvin

Griseofulvin solid dispersions

were prepared using polyethylene

glycol 6000 (PEG), talc, and their

combination as carriers by the

solvent evaporation method (83).

Dispersions of PEG and PEG/talc

provided dissolution rates faster

than those from dispersions of

talc.

2 Nifedipine The drug to carrier ratios of 1:1

and 1:9 were used for preparing

both solid dispersion and

physical mixtures by solvent

evaporation method (84).

The dissolution rate of nifedipine

was successfully achieved by

surface solid dispersion

technique.

3 Carbamazepine Solid dispersions of

carbamazepine (CBZ) were

formulated by supercritical fluid

processing (SCP) and

conventional solvent evaporation

in polyethylene glycol (PEG)

8000 with either Gelucire 44/14

or vitamin E TPGS NF (d-α-

tocopheryl PEG 1000 succinate

(85).

Polymorphic change of CBZ

during SCP led to faster

dissolution. Therefore, SCP

provides advantages over solid

dispersions prepared by

conventional processes.

Table 3.0 Drugs that have been formulated as solid dispersions and polymer used

41

4 Albendazole Solid dispersions were prepared

using three different carriers,

mixing ratios and methods in an

attempt to improve the solubility

and dissolution rate of

albendazole (ABZ). Carrier

includes urea, polyethylene

glycol 6000 (PEG) and

poloxamer 407 (PXR) (86).

The result showed that PXR

system showed the highest

dissolution rate with respect to

pure drug for all mixing ratios

and methods of preparation.

5 Nimodipine Solid dispersions of the drug

nimodipine using polyethylene

glycol as carrier were prepared

following the hot-melt method

(87).

6 Ofloxacin (OFX) Solid dispersions of a water-

insoluble ofloxacin (OFX) with

polyethylene glycol (PEG) of

different molecular weights were

prepared. Polysorbate 80, a non-

ionic surfactant, was also

incorporated into the

The result indicated that

amorphous OFX existed in the

solid dispersions with high drug

loading and remarkably

improved dissolution of drug

from the ternary solid dispersion

systems when compared with the

42

soliddispersion systems as the

third component to obtain the

ternary solid dispersion systems

(88).

binary solid dispersion systems.

7 Valdecoxib Solid dispersions of valdecoxib

with mannitol, polyethylene

glycol 4000, and polyvinyl

pyrrolidone K-12, were prepared

to overcome problem of its very

low solubility in biological fluids

and poor bioavailability after oral

administration(89).

The dissolution of valdecoxib has

improved considerably from PVP

K-12 solid dispersions as

compared to mannitol, and PEG-

4000 solid dispersions.

8 Chlordiazepoxide Solid dispersions of

chlordiazepoxide were prepared

by using three carriers PVP,

mannitol and eudragit E by

solvent evaporation method (90).

This study showed that addition

of PVP to chlordiazepoxide

improved its dissolution rates.

9 Zaleplon Zaleplon solid dispersion was

prepared with poloxamer F68,

polyvinylpyrrolidone K30 (91).

The study showed that the

dissolutionrate of zaleplon can be

enhanced by solid dispersion

technique using solvent

43

evaporation method.

10 Prednisone Prednisone dispersions were

prepared using polyethylene

glycol (PEG) 6000 as a carrier at

low and high concentration (92).

The results showed a

significantly higher prednisone

dissolution (80% within 30

minutes) than did conventional

tablets prepared without PEG

6000 (<25% within 30 minutes).

11 Gliclazide The solubility and dissolution

rate of gliclazide was enhanced

by formulating solid dispersions

of gliclazide with PVP K90 (93).

The solubilization effect of PVP

K90, reduction of particle

aggregation of the drug,

formation of microcrystalline or

amorphous form of drug,

increased wettability,

dispersibility, and development

of intermolecular hydrogen

bonding were responsible for the

enhanced solubility and

dissolution rate of gliclazide

from its solid dispersion.

44

12 Meloxicam (MLX) Solid dispersion were prepared

using a hydrophilic polymer,

poloxamer 188 (PXM) by

kneading technique (94).

The results of the study

confirmed that the factors

polymer ratio significantly

influences the dependent

variables dissolution efficiency at

60 min and the kneading time

13. Lamotrigine (LMN) Binary systems of LMN and

Hydroxy propyl β-cyclodextrin

(HP β-CD) were prepared in

different molar ratios (1:1, 1:2,

1:3 and 1:4) by kneading method

(95).

The entire drug was entrapped

inside the HP β-CD cavity and

reduction in drug crystallinity

also took place, which may be

responsible for improved

dissolution characteristics as

compared to that of the pure

drug.

14. Diazepam Fast dissolving tablets of

diazepam were prepared by wet

granulation and direct

compression methods using solid

dispersion of drug (96).

Solid dispersions of diazepam

and PEG-6000 (1:2.5, 1:5 and

1:10) were prepared by using the

mentioned methods and it was

concluded that it can be used in

emergency treatment of anxiety

disorder and seizures.

45

15.

Paracetamol

Solid dispersions of paracetamol

were prepared using PEG 4000,

PEG 6000 and urea by fusion

method (97).

46

1.13 RECENT ADVANCES AND FUTURE ASPECTS

Solid dispersion has great potential both for increasing the bioavailability of drug and

developing controlled release preparations. Thus, to solve bioavailability issues with respect

to poorly water-soluble drugs, solid dispersion technology has grown rapidly. The dosage

form can be developed and prepared using small amounts of drug substances in the early

stages of the drug development process; the system might have an advantage over such other

commonly used bioavailability enhancement techniques as micronization of drugs and soft

gelatin encapsulation. There are some major research areas where focus must be given in

context to solid dispersion which include:

I Identification of New Surface-Active Carriers and Self-Emulsifying Carriers

A major focus of future research will be the identification of new surface-active carriers and

self-emulsifying carriers for solid dispersions. Only a small number of such carriers are

currently available for oral use. Some carriers that are used for topical application of drug

only may be qualified for oral use by conducting appropriate toxicological testing (98).

II New Vehicles

Research should also be directed toward identification of vehicles or excipients that would

retard or prevent crystallization of drugs from supersaturated systems. Attention should also

be given to any physiological and pharmacological effects of carriers used. Many of the

surface-active and self-emulsifying carriers are lipidic in nature, so potential roles of such

carriers on drug absorption, especially on their p-glycoprotein-mediated drug efflux, require

careful consideration (98).

III Extended-Release Dosage Forms

To extend the release rate dosage form has been reinvigorated by the availability of surface-

active and self-emulsifying carriers and the development of new capsule filling processes.

Because the formulation of solid dispersion for bioavailability enhancement and extended

47

release of drugs may employ essentially similar processes, except for the use of slower

dissolving carriers for the latter use, it is expected that the research in these two areas will

progress simultaneously and be complementary to each other(98).

IV Bioavailability Enhancement

Solid dispersions have shown promising future for both increasing the bioavailability of

drugs and for developing controlled release preparations. Few successful developments of

solid dispersion systems for preclinical, clinical and commercial use have been feasible in

recent years due to the availability of surface-active and self-emulsifying carriers with

relatively low melting points (99).

48

1.14 STATEMENT OF RESEARCH PROBLEM AND JUSTIFICATION OF

STUDY

Diabetes mellitus is the commonest endocrine-metabolic disorder characterized by chronic

hyperglycaemia giving rise to the risk of microvascular (retinopathy, nephropathy, and

neuropathy) and macrovascular (ischaemic heart disease, stroke and peripheral vascular

disease) damage, with associated reduced life expectancy and diminished quality of life.

Recent estimates indicate there were 171 million people in the world with diabetes in the year

2000 and this is projected to increase to 366 million by 2030. This increase in prevalence is

expected to be more in the Middle Eastern crescent, Sub-Saharan Africa and India (100). In

Nigeria alone, the population of people with this disorder by 2000 was 1,707,000 and

proposed to increase to 4,835,000 by 2030. In Africa, the estimated prevalence of diabetes is

1% in rural areas, up to 7% in urban sub-Sahara Africa, and between 8-13% in more

developed areas such as South Africa and in population of Indian origin (101).

The prevalence in Nigeria varies from 0.65% in rural Mangu (North) to 11% in urban Lagos

(South). Besides, data from the World Health Organization (WHO) suggests that Nigeria has

the greatest number of people living with diabetes in Africa (102).

As at the year 2003, the numbers of people affected by diabetes in Sub-Saharan Africa are

namely Nigeria (about 1.9 million people), South Africa (841,000), the Democratic Republic

of Congo (552,000), Ethiopia (550,000), and Tanzania (380,000). The rate at which new

cases of diabetes are emerging poses an additional burden on a country already stretched to

the limit by common life-threatening infections, such as malaria, tuberculosis, and HIV and

Acquired Immune Deficiency Syndrome (AIDS) (103).

The International Diabetes Federation estimated that, in 2003, more than 46 percent (3.3

million) of the diabetic population were 40 to 59 years old, whereas 28 percent and 26

percent, respectively, were 20 to 39 and 60 to 79 years old. This has serious implications for

49

the productivity of the region, since diabetes affects the active members of the community.

The escalating prevalence of type 1 and type 2 diabetes and their complications in sub-

Saharan Africa are a major drain on health resources in financially difficult circumstances, in

addition to having a considerable physical and social impact on the individual and

community (104).

Diabetes mellitus is a major cause of morbidity and mortality, worldwide (105). There are

majorly three types of diabetes mellitus namely Type I, type II and gestational diabetes.

However,about 90 percent of people with diabetes have type II. In type 2 diabetes mellitus,

the pancreas does not make enough insulin. Consequently, the body becomes resistant to

normal or even high levels of insulin, or both. This causes high blood glucose (blood sugar)

levels, which can cause complications, if untreated (106). It is a chronic medical condition

that requires regular monitoring and treatment throughout life. Treatment includes lifestyle

changes, self-care measures, use of medications and a combination of all. The use of

qualitative and efficacious drugs is a very important factor in the control and decrease in the

progression of this disorder. The seriousness of diabetes is largely a result of its associated

complications, which can be serious, disabling, and even fatal.

Sulphonyl ureas, especially the second generation agents such as glimepiride, are a major

therapeutic agent used for treatment. The poor solubility of glimepiride and also some other

agents in the same class can therefore impact negatively on bioavailability with grave

implications for development of complications in the long run.

There is the need therefore, to search continuously for better ways of formulating this drug in

order to maximize efficacy. It is thus essential to focus all efforts on the research and

development of the effective delivery of this compound. This work is focused on the

formulation of solid dispersions and the solubilisation effect on glimepiride, as these may

provide a useful approach to produce novel glimepiride formulations with high

50

bioavailability. Designing and producing a medicine that will give improved systemic

bioavailability will be an immense contribution in the effort to control the progression of

diabetes.

1.15 AIM OF RESEARCH

The Present studyinvestigates the possibility of enhancing the solubility, and hence the

bioavailability of a poorly water soluble drug, glimepiride, via formation of polyethylene

glycol-polyvinyl caprolactam - polyvinyl acetate grafted copolymer (Soluplus®) and PEG

4000 based solid dispersions by solvent evaporation technique.

1.16 OBJECTIVES OF RESEARCH

i. To investigate how Soluplus®and PEG 4000 affect the solubility of glimepiride.

ii. To prepare solid dispersions of glimepiride based on Soluplus®

and PEG 4000 using

solvent evaporation method.

iii. To estimate the drug content of the solid dispersions

iv. To investigate the flow properties of the prepared solid dispersions.

v. To investigate Soluplus® -PEG 4000- glimepiride interaction using, fourier transform

infra-red spectroscopy (FT–IR) and differential scanning colorimetry (DSC).

vi. To evaluate the dissolution characteristics of the prepared solid dispersions and

compare with commercially available products.

vii. To carry out stability studies of the solid dispersions.

51

1.17 RESEARCH HYPOTHESIS

NULL HYPOTHESIS

Solid dispersions of glimepiride based on Soluplus®and PEG 4000 will not show increased

solubility and dissolution rate compared to the plain drug.

52

CHAPTER TWO

MATERIAL AND METHODS

2.1 MATERIALS

2.1.1 Chemicals and Reagents

The pure sample of glimepiride used was a generous gift by May & Bayer Pharmaceutical

Ltd, Nigeria. Soluplus®(polyvinyl - caprolactam- polyvinyl acetate - polyethylene glycol

grafted copolymer) and polyethylene glycol (PEG) 4000 (BASF, Ludwigshafen, Germany)

were purchased. Methanol and dichloromethane (Sigma Aldrich, Steinheim, Germany) were

purchased. The brand of commercially available glimepiride tablet used is stated in Table 4.0.

All other chemicals and reagents used were of analytical grade and obtained commercially.

Table 4.0 Brand of marketed formulation used

Brand Batch no. Man. Date Expiry date Country of

Origin.

Amaryl®

tablets

X1571

Jan. 2012

Dec. 2013

Switzerland

2.1.2 Animals

Mature albino rats weighing between 100-200 g obtained from the Department of

Pharmacology and Toxicology’s animal utility house, University of Nigeria Nsukka were

used for the study. All the rats were allowed to equilibrate in standard and conditioned animal

house for a period of one week before use.

53

2.2 METHODS

2.2.1 Identification of Glimepiride

I. Melting point determination

The melting point of the drug sample was determined using electrothermal melting point

apparatus. A small quantity of the drug was incorporated into a capillary tube and heated.

The temperature at which the drug completely melted was noted and recorded.

II Differential scanning calorimetry (DSC) of the drug sample

DSC analysis of drug sample was carried out. Approximately 2-5 mg of each sample was

placed in a sealed aluminium crucible,heated at a scanning rate of 10ºC/min and

temperature range of 25-250˚C under steam of nitrogen.

2.2.2 Preparation of Reagents

2.2.2.1 Preparation of Simulated body fluids

I. Preparation of simulated intestinal fluid (SIF)

A 6.8 g quantity of potassium dihydrogen phosphate was dissolved in 77 ml of 0.2 N

sodium hydroxide and the volume made up to 1000 ml. The pH was adjusted to 7.4 by

adding drops of 0.2 N sodium hydroxide (107).

II. Preparation of simulated gastric fluid (SGF)

A 2 g quantity of sodium chloride was dissolved in 7 ml of concentrated Hydrochloric

acid and the volume made up to 1000 ml with distilled water, the pH was adjusted to 1.2

by adding drops of concentrated HCl (107).

54

2.2.3 Calibration curve of Glimepiride

The calibration curve was constructed by analyzing five different concentrations of standard

solutions (50 – 800 µg/ml) prepared on the same day. All determinations were conducted in

triplicate at a predetermined wavelength of 236 nm (108).

I. Preparation of Standard solution

Standard stock solution (1000ug/ml) was prepared by transferring 100mg of glimepiride

into a 100ml volumetric flask, 30ml of 0.1M sodium hydroxide was added to dissolve the

drug. The volume was made up to the 100ml mark with methanol. Aliquot of the standard

solution was transferred using A-grade bulb pipette into 10ml volumetric flasks and made

up to volume with methanol to get final concentrations.

II. Determination of Absorption maxima

The standard stock solution (approximately 3 ml) was scanned from 200 to 400nm with

fixed slit width of 2.0 nm using methanolic NaOH as blank. The wavelength of maximum

absorption was recorded.

III. Analyses of samples

The different concentrations prepared were analysed using a UV / Visible

spectrophotometer (Jenway 6405, Germany) at a wavelength of 236 nm against a blank

made up of methanolic NaOH. The absorbances of the different concentrations were

recorded.

2.2.4 Preparation of Glimepiride Solid Dispersions

The solid dispersions of glimepiride were prepared by solvent evaporation technique using

Soluplus®and PEG 4000 as carriers. The drug and carriers were accurately weighed in

55

different ratios and dissolved in minimum quantity of dichloromethane and methanol

respectively. The resultant solutions were mixed in a beaker. The solvents were removed by

heating at a constant temperature of 40oC. The residues were transferred to an aluminum

pan and allowed to dry at room temperature. The dried samples were pulverized and passed

through a 100-mesh screen. The resultant solid dispersions were packed in screw cap

containers and stored in desiccators for further use(using silica gel as desiccant) (109-112).

2.2.5 CHARACTERIZATION OF THE SOLID DISPERSIONS

2.2.5.1 Differential Scanning Calorimetry (DSC)

DSC analysis were performed on the drug sample, Soluplus®, PEG 4000 and the solid

dispersions using differential scanning calorimeter. Approximately 2-5 mg of each sample are

placed in a sealed aluminium crucible, heated at a scanning rate of 10 ºC/min and temperature

range of 25-250 oC under steam of nitrogen (113).

2.2.5.2 Fourier Transform Infrared (FTIR) analysis

FT-IRanalyses of samples werecarried out. This analysis was employed to characterize the

possible interactions between the drug and the carrier in the solid state. Samples of about 2

mg were lightly ground and mixed with IR grade dry potassium bromide and then

compressed at 10 tonnes in a hydraulic press for 5 min to form discs. The spectra of the drug

sample, Soluplus®, PEG 4000 and the selected solid dispersion formulations (SP1, S1, P1)

were scanned over a frequency range 4000–5000 cm-1 with a resolution of 4( 114-116).

2.2.6 Estimation of drug content

Solid dispersions equivalent to 1 mg of drug were taken and dissolved in 20 ml of methanol

and filtered. Then the filtrate was suitably diluted with phosphate buffer, pH 7.4, and the drug

content was analyzed againsta blank made up of methanolic phosphate buffer usinga

56

UV/Visible spectrophotometer (Jenway 6405, Germany)at 236 nm. The concentration of drug

present in solid dispersion was compared with that of standard solution containing 1 mg of

pure drug. The percentage of drug present in the solid dispersions was calculated with respect

to standard concentration(117,118).

2.2.7 Determination of percentage yield

The practical yields of the solid dispersions were determined to evaluate the efficiency of the

method of preparation by measuring their weights. The percentage yields were calculated

using the formula stated in Equation 1. (119)

������������� ��������������������������������

���������������� 100 ……Eqn. 1

2.2.8 Micromeritic properties of the Solid dispersion

The importance of considering the particle properties of a pharmaceutical material for direct

compression in oral dosage forms cannot be over emphasized. This is because powder flow,

compression and other important processes depend on the particle properties (120). The flow

properties of the solid dispersions were evaluated using the following empirical parameters:

angle of repose (θ), Hausner’s quotient and Carr’s compressibility index (121). A 5 g quantity

of the solid dispersions was allowed to fall freelyfrom a plastic funnel (efflux tube length =

4.5 cm) clamped to a retort stand onto a white piece of paper. The resulting height of the

powder heap, h, and the diameter, d, of the base were measured. The bulk and the tapped

density of the powders (expressed in g/ml) were also determined. A known weight, 5 g, each

of the solid dispersions was poured into a calibrated 25 ml measuring cylinder. The unsettled

apparent volume and the final tapped volume were measured. Equations 2, 3 and 4 were used

to calculate the different parameters.

57

Angle of repose ……………….Tan & '�

�……………Eqn.2

Hausner’s quotient ……………..() *�

*�……………..Eqn.3

Carr’s Compressibility index……+, -*�.*�/

*� 100…Eqn.4

Where h = height of the powder heap

d = diameter of the base heap

Vo = unsettled apparent volume

Vf = final tapped volume

2.2.9 In vitro drug dissolution

The in vitro drug dissolution properties of the formulated solid dispersions, pure glimepiride

drug sample, and commercially available glimepiride tablet (Amaryl®) wereexamined using

USP dissolution apparatus II(flask stirrer-method) and in different dissolution media (SGF

pH 1.2 and SIF pH 7.4). Samples equivalent to 2 mg of glimepiride were placed in a dialysis

membrane immersed in 500 ml of dissolution media maintained at a temperature of

37 ±0.2 oC and stirred at 50 rpm.Sample aliquots (3 ml) were withdrawn at time intervals (5,

10, 15, 30, 45, 60, 75, 90, 105, 120 min) and replaced with same volume of fresh medium to

maintain sink conditions.The absorbanceofthe drug in each sampled aliquot was determined

spectrophotometicallyat wavelength of 236nm. The concentration of glimepiride was then

estimated from the standard calibration curve that was linear over the UV absorbance range

(122).

2.2.10 Determination of In vivo antidiabetic activity

A total number of 30 albino rats weighing about 100-200 g(age: 3months)were used to

evaluate the hypoglycemic activity of the formulations. The animals were kept in a cage

58

inside a well ventilated animal house and maintained on standard diet under controlled

conditions of humidity (30 - 70 %) and temperature (27 ± 2oC). The animals were randomly

divided into 5 groups (n = 6), starved for 12 h, and their baseline glucose level determined.

Diabetes was induced by injecting intraperitoneally a freshly prepared solution of alloxan

(Sigma-Aldrich, Hamburg, Germany)(150mg/kg) in normal saline for all the groups. After 48

h, blood samples from the tail vein of the animals were collected and the blood glucose level

measured with a glucometer(Accu-check, Roche, USA). The animals having moderate

diabetes with blood glucose level above 200 mg/dlwere selected for the study. The last two

groups (group D and E) were treated with normal saline(negative control) and glimepiride

tablets(positive control) at a dose of 5 ml/kg and 0.0285 mg/kg body weight respectively.

Group A and C rats were given the formulations (SP3 and SP1) while group B rats were given

pure glimepiride sample at a dose of 4.285 and 0.0285 mg/kg body weight respectively. All

the treatments were administered orally.Blood samples of the animals were collected

afterwards from the tail vein at time intervals of 0, 1, 3, 6, 9, 12, 15, 24 handtested for blood

glucose level usingthe glucometer (123).

2.2.11 Stability studies

The stability studies of the different batches of glimepiride solid dispersions were analysed

according to International Conference of Harmonization (ICH) guidelines (40 ± 2ºC and 75 ±

5% RH) for periods of three months and sixmonths in a humidity chamber. The formulations

were packed in amber colored bottles. After three and six months, samples were withdrawn

and re-evaluated for the drug content, (124).

2.2.12 Statistical analysis

All experiments were performed in replicates for validity of statistical analysis. Results were

expressed as mean ± SD. ANOVA and Student’s t-test were performed on the data sets

59

generated using Statistical Package for Social Sciences (SPSS) software, version 12

( Chicago, IL). Differences were considered significant at p-values < 0.05.

60

CHAPTER THREE

RESULTS AND DISCUSSION

3.1 Identification of pure drug sample

The melting point determinations were conducted to confirm the authenticity and purity of

the pure drug sample. The drug was identified by its melting point. The melting point of the

drug sample (205-209 oC) agreed with the literature value confirming the sample as

glimepiride and also ascertaining its purity. The purity of the glimepiride sample was further

ascertained from it DSC thermogram which showed an endothermic sharp peak at 209oC

corresponding to its melting point.

3.2 Practical yield of solid dispersions

Different batches of glimepiride solid dispersion were successfully and suitably prepared by

solvent evaporation method. The variations in polymer ratio were represented with different

formulation codes as shown in Table 5.0. From the results, the practical yield of the solid

dispersions prepared was excellent and ranged from 95 – 98 %. S2 and SP1 formulations have

the highest and least practical yield respectively. The small losses may have occurred during

the process of preparation through weighing, mixing, transfers, etc.

3.3 Morphology and Physical appearance

The solid dispersions with the aid of visible eyes were powdery and white to milky-white in

colour. Photo-micrographs showing the morphology of the different solid dispersion

formulations are presented in the Figs 8.0 – 18.0. The photo-micrographs depict white to

milky – white coloured solid dispersions. Furthermore,they showed that discrete, flowable

and spherical to irregularly- shaped solid dispersions were been successfully prepared with

PEG 4000 and Soluplus®matrices.

61

Table 5.0 Different formulations of glimepiride solid dispersions prepared and their

practical yield.

Key: Glim - Glimepiride, Sol –Soluplus®

, PEG – Polyethylene glycol 4000

Batch code Formulation

type

Ratio of

polymer used

( Sol :PEG)

Solvent used Percentage (%)

yield

S1 Glim: Sol 1: 0 Methanol and

dichloromethane

96.23

S2 Glim:Sol 1:0 Methanol 97.82

P1 Glim:PEG 0:1 Methanol and

dichloromethane

97.36

P2 Glim: PEG 0:1 Methanol 97.44

SP1 Glim:PEG: Sol 1:1 Methanol and

dichloromethane

95.66

SP2 Glim:PEG: Sol 1:2 Methanol and

dichloromethane

97.66

SP3 Glim: PEG: Sol 1:5 Methanol and

dichloromethane

96.00

SP4 Glim:PEG:Sol 5:1 Methanol and

dichloromethane

97.23

SP5 Glim:PEG:Sol 1:1 Methanol 97.24

62

Figure8.0Photomicrograph of pure glimepiride drug sample (x 100)

Figure 9.0Photomicrograph of Polyethylene glycol 4000 (x 100)

63

Figure 10.0Photomicrograph of Soluplus®(x 100)

Figure 11.0Photomicrograph of batch S1 formulation (x 100)

64

Figure 12.0Photomicrograph of batch S2 formulation (x 100)

Figure 13.0Photomicrograph of batch P1 formulation ( x 100)

65

Figure14.0Photomicrograph of batchP2 formulation (x 100)

Figure 15.0Photomicrograph of batch SP1 formulation (x 100)

66

Figure 16.0Photomicrograph of batch SP2formulations (x 100)

Figure 17.0Photomicrograph of batch SP4 formulation(x 100)

67

Figure 18.0Photomicrograph of batch SP5 formulation (x 100)

68

3.4 Drug content:

The drug content in the various solid dispersions prepared was estimated

spectrophotometrically by measuring the absorbance at predetermined wavelength. All the

formulation batches were found to have excellent entrapment of the drug. The glimepiride

drug content in all the solid dispersions were found to be in the range of 70 - 90%

approximately, as shown in Table 6.0. However, batch SP1 solid dispersion prepared with

equal ratio of the polymers showed the highest drug content while batch P2solid dispersion

had the least drug content. Furthermore, from the results it can be depicted that the batches of

solid dispersion prepared with Soluplus®alone, Soluplus® and PEG combinations at different

ratioshad better drug entrapment.

3.5 Micromeritic properties of the solid dispersions

The compressibility index and Hausner’s quotient are measures of the propensity of a powder

to be compressed. They permit an assessment of the relative importance of inter-particulate

interactions. The flowability of the solid dispersions is based on inter-particulate

cohesionwhich was assessed by determination of angle of repose. Table 7.0 shows the

Hausner’s quotient, Carr’s compressibility index, and angle of repose for the various batches

of soliddispersions. As a general rule, particles with angle of repose values < 25, 25-30, 31-

35, 36-40, 41-45, 46-55and > 56 are considered to have excellent, very good, good flow

properties, fair, passable flow, poor and very poor flow, respectively (125). From the result

shown in the table, the solid dispersions had angle of repose values that ranged from 8 – 20

degrees, depicting an excellent flow property. Hausner’s quotient (HQ) values approximate to

1.2 have been reported to indicate good flow characteristics for a powder (126). The results

inthe table shows HQ values in the range of 1.0 to 1.16 , implying that the solid dispersions

have excellent flow ability. Theoretically, Carr’s index values of 5-15 %, 12-16 % and 18-21

% indicate excellent, good, and fair flow, respectively. Thus, from the results shown in the

table, the various batches of solid dispersion with Carr’s indices ranging from 5 – 13.5 %

generally have excellent flow.

69

Table 6.0Drug content of the different batches of solid dispersions.

Formulation Code Drug Content (%)

P1 77.7

P2 70.0

S1 81.1

S2 72.2

SP1 88.8

SP2 85.5

SP3 86.6

SP4 78.8

SP5 76.6

70

Figure 19.0 Bar chart representing the percentage (%) drug content of the

formulations

0

20

40

60

80

100

120

P1 P2 S1 S2 SP1 SP2 SP3 SP4 SP5

Pe

rce

nta

ge

dru

g c

on

ten

t (%

)

Formulation codes

71

Table 7.0Micromeritic properties of the different formulations

Formulation Code Angle of repose (degrees)

Hausner’s quotient Carr’s index (%)

S1 16.69 ± 0.17 1.129 11.42

S2 17.28 ± 0.04 1.150 13.51

P1 19.09 ± 0.05 1.133 11.76

P2 20.67 ±0.09 1.147 12.79

SP1 8.13 ±0.03 1.125 11.11

SP2 18.12 ± 0.06 1.062 5.88

SP3 19.79 ± 0.29 1.079 7.32

SP4 19.98 ± 0.38 1.125 11.11

SP5 9.73 ± 0.32 1.133 11.76

72

3.6 In vitro drug dissolution studies

The dissolution studies of glimepiride as pure drug, its solid dispersion and commercially

available product were performed in simulated gastric fluid (pH 1.2) and simulated intestinal

fluid (pH 7.4) by using USP-II dissolution method. Based upon the data obtained from the

dissolution studies, the amount of drug dissolved at specific time periods was plotted as

percentage (%) drug release versus time (min) curves. Various parameters such as first order

release kinetics R2 values andT50were estimated, as shown in Table 8.0. The dissolution rate

of the different batches of solid dispersions was found to be significantly (p < 0.05)more

rapid when compared to the pure drug in both acidic and alkaline mediaas indicated by their

T50 values from curves shown in Figures20.0 and 21.0. In SIF, the formulations also showed

more rapid dissolution compared to the commercially available product except for batch P2

formulation. In the first 30 min, percentage (%) drug released from the formulations was

65.83, 57.93, 58.47, 51.45, 80.83, 81.67, 84.02, 70.97, 71.13 and 46.80 % for batches S1, S2,

P1, P2, SP1, SP2, SP3, SP4, SP5 formulations and the commercially available product

respectively, in alkaline medium.At the end of 120 min, batch SP3 formulation showed

maximum percentage (%) drug release of 96.11 and 57.08 % in SIF, pH 7.4 and SGF, pH 1.2

respectively, while batch P2 had the least percentage (%) drug release of 74.55 and 40.55 %

in SIF, pH 7.4 and SGF, pH 1.2 respectively. In addition, the solvent system employed in the

preparation of the solid dispersions was found to have an impact on the dissolution rate of the

solid dispersions. From the graphs shown in Figures 22.0 and 23.0, asignificant (p < 0.05)

reduction in the values of percentage (%) drug released at 30 minutes was observed when

methanol was used as a solvent to prepare batches SP5, S2 and P2 formulations. The reason

can be attributed to less solubility of glimepiride in methanol as compared to the co-solvent

and dichloromethane alone.Furthermore, the results indicated that as the concentration of the

polymer in the dispersed system, especiallySoluplus® increased, dissolution of glimepiride

73

increased. In all cases, solid dispersions recordedfaster and almost complete dissolution

compared to the pure drug. They also followed first order release kinetics with their

regression coefficients shown in Table 8.0. The possible mechanisms responsible for

increased dissolution could be reduction of crystalline size, a solubilisation effect of the

carrier, absence of aggregation of drug crystallites, improved wettability and dispersibility of

the drug from the dispersion, dissolution of the drug in the hydrophilic carrier and conversion

of the drug to an amorphous state. As the soluble carrier dissolves,the insoluble drug gets

exposed to dissolution medium in the form of fine particles for quick and faster dissolution

(120).

74

Figure 20.0 Dissolution profile of glimepiride, its solid dispersions and marketed

product in SIF, pH 7.4

0

20

40

60

80

100

120

0 20 40 60 80 100 120 140

Per

cen

tag

e d

rug

rel

ease

(%

)

Time (min)

S1

P1

SP1

SP2

SP3

SP4

Glimepiride

Amaryl

75

Figure 21.0Dissolution profile of glimepiride, its Solid dispersions and commercially

available product in SGF, pH 1.2

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120 140

Per

cen

tage

dru

g r

elea

se (

%)

Time ( min)

Glimepiride

P1

S1

SP1

SP2

SP3

SP4

76

Figure 22.0 Dissolution profile of batch S2, SP5 and P2 solid dispersions in SGF, pH 1.2

compared with that of S1, SP1 and P1

0

10

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140

Per

cen

tag

e d

rug

rel

ease

d (

%)

Time (min)

SP5

S2

P2

SP1

S1

P1

77

Figure 23.0 Dissolution profile of batch S2, SP5 and P2 solid dispersions in SGF, pH

1.2 compared with that of S1, SP1 and P1

0

10

20

30

40

50

60

0 20 40 60 80 100 120 140

Per

cen

tag

e d

rug r

elea

sed

(%

)

Time (min)

SP5

S2

P2

SP1

S1

P1

78

Table 8.0 Parameters from the dissolution studies

Formulation code SIF pH 7.4 SGF pH 1.2 First order

Regression

Coefficient

(R2)

% Drug

released at 30

min (%)

T50 (min) % Drug

released at 30

min (%)

T50 (min)

S1 65.83 12.67 41.80 46.0 0.9088

S2 57.93 15.61 36.78 > 120 0.8852

P1 58.47 13.38 35.83 > 120 0.9561

P2 51.45 16.58 31.53 > 120 0.9310

SP1 80.83 8.45 34.58 > 120 0.9190

SP2 81.67 15.61 27.77 60 0.9163

SP3 84.02 8.18 43.05 34.8 0.9083

SP4 70.97 8.65 40.41 > 120 0.8978

SP5 71.13 9.60 30.43 > 120 0.8605

Amaryl® 46.80 32.05 - -

79

3.7 FTIR Spectroscopy

The IR spectrum of a given compound is always unique and characteristic. Thus IR

spectroscopy is a quick and relatively cheap technique for identifying compounds (105). IR

spectroscopy detects variation in the energy distribution of interactions between the drug and

matrix. In other words, the analysis was carried out to rule out any interaction between the

drug and the matrices used. TheFT-IR spectra of PEG 4000, physical mixture of PEG

4000/Soluplus®,pure drug sample, Soluplus®sample, and thedifferent batches ( SP1 , P1, S1) of

the solid dispersions are shown in Figs 24.0 – 30.0respectively.

The FTIR spectrum of the pure drug sample (as shown in Fig 26.0) shows principal peaks at

607.70, 1156.36, 1343.46 , 1543.10 and 1691.63, 3368.79 and 3286.81 corresponding to N-

H bending out of plane vibrations , sulphonate (S=O) stretching vibrations, C-N stretching

vibrations, C=O stretching and N-H bending vibrations, asymmetric and symmetric N-H

stretching vibrations respectively.

The FTIR spectrum of the PEG 4000 sample only ( Fig 24.0 ), shows principal peaks at

841.96, 951.90, 1112.96, 1271.13, 1351.18, 1464.98,2883.68 and 3438.23 corresponding to

aromatic C-H bending ( in plane bend) vibrations, aromatic C-H bending ( out of plane)

vibrations, C-O stretching (strong), C-O stretching in plane O-H bend, C-H deformation,

O=C-H stretching and OH stretching respectively.

The FTIR Spectrum of the Soluplus®sampleonly(as inFig 27.0) shows principal peaks at

1109.11 and 1247.02, 1452.45, 1626.05 and 1726.35, 2928.04 and 3465.23. This corresponds

to a symmetric and asymmetric C-O-C (alkyl substituted ether) stretching vibrations,

methylene bend vibrations, carbonyl gp C=O stretching characteristic of a carboxylate and

other compounds, methylene C-H asymmetric and symmetric stretching and OH stretching

vibrations.

80

The FTIR spectra of the different batches of solid dispersions S1 andSp1as shown in Figs30.0

and 28.0 respectively, revealed almost all the bands of the drugwithout affecting the

characteristic peak positions and trends,which indicates absence of well-defined interactions

between the drug and the polymer.

Furthermore, the FTIR spectrum of the physical mixture of PEG 4000 andSoluplus®

( in the

ratio of 1:1) as shown in Fig 25.0, revealed almost all the characteristic peak positions of

PEG 4000 and Soluplus® indicating absence of well-defined interactions between the two

matrices or formation of a new compound.

The FTIR spectra of the different batches of solid dispersion P1 and SP1 as shown in Figs

29.0 and 28.0respectively, revealed almost all the peaks of the drug which indicates absence

of any interaction between the drug and the matrix.

81

3.8 Differential Scanning Calorimetry (DSC)

The differential scanning calorimeter (DSC) can be used to evaluate drug carrier miscibility,

amorphous content, stability, etc. The slight presence or total absence of a melting peak in the

DSC of a solid dispersion indicates that the drug is partly or completely

amorphous/molecularly dispersed (127). The DSC thermogram of Soluplus®

, the drug

sample, PEG 4000, physical mixture of Soluplus®

/PEG 4000and different batches (S1, P1 and

SP1) of solid dispersions are shown in Figs31.0 – 37.0. The thermograms of all the above

listed samples superimposed is shown in Fig 38.0, while that of Soluplus®, the pure drug

sample and S1 solid dispersion superimposed is shown in Fig 39.0.

The thermograms of the pure drug sample and PEG 4000 showedsharp endothermic peaks at

209.7 ˚C and 64.5˚C indicating the melting points of eachsubstance,respectively. The DSC

thermogram of the physical mixture of Soluplus® and PEG 4000 showed an enothermic peak

at 65.7 ˚C almost corresponding to the melting point of PEG 4000. Furthermore the DSC

thermograms of P1 and SP1 batches of solid dispersions showed no endothermic peak of the

drug indicating that the drug was efficiently dispersed molecularly in its amorphous form.

However, the peaks of PEG 4000 in these batches were found to be shifted probably due to

solid-solid phase transition. The DSC thermogram of S1 batch of Solid dispersions

preparedwith Soluplus®alone showed a slight and decreasedpeak of the drug, indicating that

the drug was partly molecularly dispersed or partly amorphous in the carrier. The amorphous

nature of the drug in the formulation confirms its usage in the improvement of solubility.

82

Figure 24.0 FTIR spectrum of Polyethylene glycol (PEG) 4000

83

Figure 25.0FTIR spectrum of Soluplus® and glimepiride physical mixture

84

Figure 26.0FTIR spectrum of glimepiride pure drug sample

85

Figure27.0FTIR spectrum of Soluplus®

86

Figure 28.0 FTIR Spectrum of batch SP1 formulation

87

Figure 29.0FTIR spectrum of batch P1 formulation

88

Figure 30.0FTIR spectrum of batch S1 formulation

Figure 31.0 Thermogarm of Soluplus®

89

Figure 32.0 Thermogram of glimepiride pure drug sample Thermogram of glimepiride pure drug sample

90

Figure 33.0 Thermogram of batch S1 formulationformulation

91

Figure 34.0 Thermogram of polyethylene glycol (PEG) 4000 pure sampleThermogram of polyethylene glycol (PEG) 4000 pure sample

92

Figure 35.0 Thermogram of Soluplus® and PEG 4000 physical mixture (ratio of 1:1)and PEG 4000 physical mixture (ratio of 1:1)

93

Figure 36.0 Thermogram of batch P1 formulation formulation

94

Figure37.0 Thermogram of batch SP1formulation formulation

95

Figure 38.0Thermograms of A1 (PEG 4000), pure drug sample, Soluplus

formulations superimposed.

Thermograms of A1 (PEG 4000), pure drug sample, Soluplus®, physical mixture of PEG 4000 and Soluplus

96

, physical mixture of PEG 4000 and Soluplus®, batch P1 SP1 and S1

Figure 39.0 Thermograms of pure drug sample, SoluplusThermograms of pure drug sample, Soluplus®, and S1 formulation superimposed

97

98

3.9 In vivo antidiabetic studies

The results of the antidiabetic studies of the formulations, the pure drug and

commerciallyavailable product are shown in Figures 40.0 and 41.0. The effect of the solid

dispersions on the blood glucose level of non-diabetic rats was assessed in comparison with

both the pure drug sample and commercial product. The reduction in blood glucose level and

percentage (%) reduction in initial glycaemia was used to evaluate the pharmacologic activity

of the formulations (SP3 and SP1), pure drug and commercially available productin vivo. The

curves obtained by plotting percentage (%) blood glucose reduction from initial glucose

levels versus time are presented in Fig 40.0. Thegroups treated with batch SP3 and SP1

formulations showed longer and more reduction in glucose level than the pure drug which is

an indication of improved performance produced by the solid dispersions. The blood glucose

reduction observed in this two groups treated with the formulations was significantly more (p

< 0.05) than that of the group treated with the commercially available product (Amaryl®

).

Furthermore, in the groups treated with the formulations, the blood glucose reduction

effectively commenced within an hour of oral administration with time to attain maximum

blood glucose reduction (Tmax) achieved in 3 h after which blood glucose level began to rise.

However, the levels did not return to the initial level at zero time within the 24 h of study.

The formulations SP1 and SP3 given to the two different groups showed 90.19 and 91.03 %

reduction in initial blood glucose respectively at Tmax of 3 h with a corresponding value of

36.47 % for the group treated with the pure drug sample and 83.57 % for that treated with the

commercially availableproduct. In comparison with the drug and commercial sample, the

formulations generally maintained the blood glucose level of the rats within the

normoglycemic level within 9-12 h. Thus, it depicts that glimepiride could be effectively

and efficiently delivered as solid dispersions based on PEG 4000 and Soluplus®. It is also

99

discernible from the results that the blood glucose lowering effect was dependent on the

polymers used and their concentrations.

3.10 STABILITY STUDIES OF THE FORMULATIONS

The results of the stability studies carried out on the different batches of the solid dispersions

are shown in Figs 42.0 and 43.0. It is evident from these figures that there was an

insignificant difference in the content of glimepiride after 6 months of storage. For instance,

the drug content obtained for batch SP3 solid dispersions were 85.00 and 84.69 % after 3

months and 6 months of storage as compared with its initial content of 86 %.

Furthermore, in batch SP1 solid dispersions, the drug contents obtained were 87.09 and 86.72

% after 3 months and 6 months of storage as compared with its initial content of 88 %. The

drug contents for batches SP2 and S1 formulations were 84.17 and 83.85 %, 79.89 and 79.01

% respectively after 3 months and 6 months of storage as compared with its initial contents of

85 and 81 % respectively. This indicates some level of stability of the drug in the

formulations prepared with the polymers individually and in combination even after some

period of storage.

100

Figure 40.0 Percentage (%) reduction of initial blood glycaemia

-100

-80

-60

-40

-20

0

20

40

60

80

100

120

0 5 10 15 20 25 30

Pe

rce

nta

ge

(%

) re

du

ctio

n i

n i

nit

ial

gly

cem

ia

Time (h)

SP1

Commercial sample

SP3

Glimepiride

Untreated group

101

Figure 41.0In vivo antidiabetic studies of solid dispersions in comparison with the drug

and commercially available product (Amaryl®

).

0

100

200

300

400

500

600

700

0 1 3 6 9 12 15 24

Blo

od

glu

cose

co

nce

ntr

ati

on

(m

g/d

l)

TIME (h)

SP1

Commercially available

product (Amaryl)

SP3

Glimepiride

Untreated group

102

Figure 42.0 Drug content of batches S1, S2, P1, P2, and SP1 formulations at specified

periods

0

10

20

30

40

50

60

70

80

90

100

S1 P1 S2 P2 SP1

Dru

g c

on

ten

t (%

)

Batches

3 months

6 months

103

Figure 43.0Drugcontent of batches SP2, SP3,SP4, and SP5 formulations at specified

periods

0

10

20

30

40

50

60

70

80

90

100

SP2 SP3 SP4 SP5

Dru

g c

on

ten

t (%

)

Batches

3 months

6 months

104

CHAPTER FOUR

SUMMARY AND CONCLUSIONS

4.1 SUMMARY OF RESULTS

The enhancement of oral bioavailability of poorly water soluble drugs remains one of the

most challenging aspects of drug development. Dissolution of drug is the rate determining

step for oral absorption of these drugs, which can subsequently affect the drug’s inherent

efficacy as a result of irreproducible clinical response. The basic goal of any drug delivery

system is to achieve steady state of blood concentration or tissue level that is therapeutically

effective and safe for an extended period of time. Currently, only 8% of new drug candidates

have both high solubility and permeability.Solid dispersions prepared with new polymer

biomaterials or surfactants with special physicochemical properties are one of the most

attractive approaches toenhance the solubility of a poorly water soluble drug as well as its

delivery.

In this study, different batches of PEG 4000 and Soluplus®

based solid dispersions of

glimepiride were suitably and successfully prepared by solvent evaporation method using

different ratios of the polymers. The different batches formulated showed excellent

morphology, flow properties, practical yield and drug content. Solid state characterisation

indicated that glimepiride was present in its amorphous form in formulations with

Soluplus®

and PEG 4000 due to efficient entrapment in polymer matrix and with no drug-

polymer interaction. The dissolution rate of all the solid dispersions was found to be

significantly (p< 0.05) more rapid when compared to pure drug in both acidic and alkaline

media, except for P2 solid dispersion, when compared with the commercial sample. The

kinetics of drug release from all the solid dispersions followed first order. Glimepiride in its

pure form had very slow dissolution rate, when compared with the solid dispersions. The

105

blood glucose reduction in albino rats by the solid dispersions was significantly (p < 0.05)

more and sustained when compared with the pure drug sample. The maximum percentage

(%) blood glucose reduction of 9.81 and 8.97 % was achieved in 3 hours for the two groups

(A and C respectively) treated with SDs batch SP1 and SP3. When the formulations were

administered to rats orally, the blood glucose concentrations significantly reduced compared

to the pure drug suggesting that thesolid dispersion could improve both the dissolution rate

and bioavailability of the drug as well.The stability studies suggest the good stability of the

drug in the formulations over a period of time.

4.2 CONCLUSIONS

Soluplus®and PEG 4000 individually or in combination could be used as a potential carrier in

the dissolution rate enhancement of poorly soluble drugs like glimepiride using solid

dispersion technique. With this technique improving the dissolution rate and thus

bioavailability of these drugs, the dose volume of the conventional drug can be further

reduced with concurrent reduction in side effects.

4.3 RECOMMENDATION

Considering the epidemiological status of diabetes worldwide, it is recommended that more

research work be carried out. Furthermore,judicious choice of the carriers could possibly

delay or slow down the release pattern of a drug formulated as a solid dispersion. The

availability of a wide variety of polymers that are themselvespoorly soluble or which swell

under aqueous conditions suggests that solid dispersions have tremendous potential which

can be harnessed for improved dissolution and controlled delivery of poorly water soluble

drugs.

106

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APPENDICES

y = 0.0989x - 0.0013

R² = 0.9884

0

0.02

0.04

0.06

0.08

0.1

0.12

0 0.2 0.4 0.6 0.8 1 1.2

Ab

sorb

an

ce

Concentration of Glimepiride (mg/ml)

Standard Calibration Curve of Glimepiride

Figure 44.0Beer’s plot of pure glimepiride (graph of absorbance against concentration in

0.1M NaOH.

120

Table 9.0 Results of invivoantdiabetic studies

Group

A(SP1)

Weight of

Animal (g)

Dose of

Alloxan

(mg)

Normal

Glycaemia

(mg/dl)

Time(hours)

0 1 3 6 9 12 15 24

H 157 23.53 84 600 55 53 90 166 270 319 400

T 179 26.92 88 -

Tr 136 20.40 94 -

RH 134 20.07 111 -

LH 122 18.41 101 491 69 62 78 220 389 389 415

Um 182 27.31 98 600 46 51 110 158 171 278 460

Group B (commercial

sample)

H 131 19.76 103 600 89 79 125 312 311 476 512

T 140 20.97 92 450 75 60 133 377 380 397 556

Tr 140 21.05 65 226 105 40 - - - - -

RH 112 16.79 93 600 600 53 - - - - -

LH 110 16.63 101 600 378 175 210 419 425 430 510

Um 180 27.04 89 -

Group C (SP3)

H 144 21.65 91 600 49 40 96 215 307 410 413

T 141 21.15 101 -

Tr 137 20.61 99 600 100 44 32 29 42 98 -

RH 131 19.69 98 253 51 48 121 265 287 370 382

LH 162 24.38 90 600 45 40 61 64 128 355 455

Um 177 26.66 76 600 68 66 76 104 152 265 397

121

Group

D

(pure

drug)

Weight of

Animal

(g)

Dose of

Alloxan

(mg)

Normal

Glycaemia

(mg/dl)

Time(hours)/Blood glucose level in (mg/dl)

0 1 3 6 9 12 15 24

H 165 24.82 88 383 388 270 343 362 389 418 551

T 178 26.75 98 428 300 210 281 384 410 421 578

Tr 173 25.99 102

RH 125 18.76 115 209 250 168 266 400 400 404 600

LH 108 16.31 117

Um 132 19.84 74

Group E (untreated

group)

H 192 28.84 82 285 422 473 589 600 600 600 485

T 146 21.94 89 600 600 600 - - - - -

Tr 165 24.89 76 529 564 580 600 600 600 600 542

RH 180 27.06 88 600 600 600 600 600 600 510 518

LH 142 21.30 81 -

Um 133 19.99 69 432 581 591 600 600 600 600 512

122

Table 10.0 Average blood glucose level of the rats for the different groups at different time intervals

Groups ( Blood glucose level in mg/dl) ± SD

A B C D E

Normal

Glycaemia(mg/dl)/ Time

(hours)

96.4 ± 9.65 90.5 ±13.60 92.5 ± 9.22 99 ± 16.34 80.8 ± 7.52

0 563.67 ± 62.93 495.20 ± 163 530.60 ± 155 340 ± 155 489.20 ± 133

1 56.70 ± 11.5 249.40 ± 232 62.60 ± 22.6 312.70 ± 69.8 553.40 ±74.9

3 55.30 ± 5.8 81.40 ± 54.1 47.60 ± 10.8 216 ± 51.26 568.80 ± 54

6 92.70 ± 16.16 156.60 ± 46.9 77.20 ± 33.83 296.70 ± 40.8 597.30 ± 5.5

9 181.33 ± 33.72 369.30 ± 53.9 135.40 ± 100.6 382 ± 19.0 600 ±0.0

12 276.60 ± 109.15 372 ± 57.4 183.20 ± 111.8 399.7 ± 10.5 600 ±0.0

15 328.70 ± 56.12 433.67 ± 39.6 299.60 ± 124.55 414.30 ± 9.07 577.50 ± 45

24 425 ± 31.22 526 ± 26 411.70 ± 31.48 576.30 ± 24.54 514.25 ± 23

i

i

Table 11.0 Results of in vitro dissolution studies in SGF, pH 1.2

Time

(min)

Drug released (ug) in SGF , pH 1.2

S1 P1 SP1 SP2 SP3 SP4 SP5 S2 P2 Drug

5 1.00 0.61 0.84 1.01 0.96 0.89 0.74 0.88 0.53 0.04

10 1.77 0.98 1.42 1.54 1.60 1.23 1.25 0.95 0.87 0.13

15 2.18 2.08 1.83 2.22 3.02 2.65 1.62 1.92 1.83 0.47

30 3.34 2.86 2.76 2.22 3.33 3.12 2.43 2.94 2.52 0.52

45 3.91 3.25 3.38 3.11 4.22 3.33 2.98 3.44 2.86 0.63

60 4.08 3.46 3.59 4.00 4.31 3.34 3.15 3.59 3.04 0.91

75 4.12 3.54 3.71 4.22 4.35 3.43 3.26 3.62 3.11 0.93

90 4.18 3.58 3.90 4.30 4.52 3.75 3.40 3.68 3.14 0.90

105 4.22 3.55 3.91 4.44 4.55 3.78 3.44 3.71 3.14 0.91

120 4.27 3.67 3.93 4.44 4.57 3.74 3.46 3.75 3.23 0.91

Table 12.0 Drug released in SIF, pH 7.4

Time

(min)

Drug released (ug) in SIF, pH 7.4

S1 P1 SP1 SP2 SP3 SP4 SP5 S2 P2 Glimepiride Amaryl®

5 2.13 1.16 2.36 2.41 2.44 2.32 2.08 1.87 1.02 0.45 1.34

10 3.15 2.98 4.63 4.67 4.73 4.56 4.07 2.77 2.63 0.47 2.06

15 4.36 4.11 5.23 5.66 5.33 5.15 4.60 3.84 3.61 0.94 3.63

30 5.27 4.67 6.17 6.53 6.72 5.67 5.69 4.63 4.11 1.04 3.75

45 7.33 5.66 6.75 7.12 7.28 6.56 5.94 6.18 4.98 1.23 4.52

60 7.33 6.34 7.34 7.38 7.41 6.83 6.46 6.44 5.58 1.11 5.09

75 7.36 6.57 7.39 7.42 7.45 7.22 6.50 6.48 5.78 2.08 5.31

90 7.37 6.77 7.44 7.55 7.66 7.26 6.55 6.49 5.96 1.67 6.44

105 7.38 6.78 7.44 7.55 7.67 7.27 6.55 6.49 5.96 2.22 6.44

120 7.38 6.78 7.44 7.55 7.67 7.32 6.55 6.49 5.96 2.16 6.45

ii

ii

Table 13.0 Percentage (%) drug released in SGF, pH 1.2

Time

(min)

% Drug concentration in SGF, pH 1.2

S1 P1 SP1 SP2 SP3 SP4 SP5 S2 P2 Pure drug

5 12.50 73.64 10.55 12.64 12.08 11.11 9.28 11.00 6.72 0.50

10 13.47 12.45 17.77 19.30 20.00 15.41 15.63 11.85 10.95 1.67

15 27.29 26.11 23.00 27.77 37.77 33.19 20.24 24.01 22.97 5.97

30 41.80 35.83 34.58 38.88 43.05 40.41 30.43 36.78 31.53 6.53

45 48.89 40.69 42.36 50.00 52.77 41.66 37.27 43.02 35.80 7.77

60 51.11 43.19 44.80 52.78 53.89 41.80 39.42 44.97 38.00 11.52

75 51.52 44.30 46.39 53.75 54.44 42.91 40.82 45.33 38.98 11.66

90 52.36 44.72 48.75 53.75 56.52 46.80 42.90 46.07 39.35 11.25

105 52.77 44.72 48.89 55.50 56.94 47.22 43.02 46.43 39.35 11.39

120 53.40 44.97 49.16 55.83 57.08 46.80 43.26 46.99 40.45 11.40

Table 14.0 Percentage (%) drug released in SIF, pH 7.4

Time

(min)

% Drug concentration in SIF , pH 7.4

S1 P1 SP1 SP2 SP3 SP4 SP5 S2 P2 Pure

drug

Amar

yl®

5 26.67 14.58 29.58 30.15 30.56 28.89 26.03 23.46 12.83 5.69 16.80

10 39.44 37.36 57.91 58.33 59.17 57.08 50.96 34.70 32.87 5.83 23.05

15 54.58 51.38 65.41 70.83 66.67 64.44 57.56 48.03 45.22 11.81 45.41

30 65.83 58.47 80.83 81.67 84.02 70.97 71.13 57.93 51.45 13.05 46.80

45 87.91 70.83 84.44 89.03 90.97 81.94 74.31 77.36 62.33 15.27 56.52

60 91.60 79.30 91.80 92.22 92.64 85.41 80.78 80.60 69.78 13.88 63.61

75 92.08 82.22 92.36 92.78 93.19 90.27 81.27 81.03 72.35 25.97 66.39

90 92.22 84.72 93.05 94.44 95.83 90.83 81.88 81.15 74.55 20.83 80.83

105 92.22 84.72 93.05 94.44 96.11 90.27 81.88 81.15 74.55 27.77 80.55

120 92.22 84.72 93.05 94.44 96.11 91.52 81.88 81.15 74.55 27.08 80.70

iii

iii

Table 15.0 Percentage reduction in initial glycaemia

Table 16.0 Drug Content of formulations after a specified period of time

Batches Drug Content (%)

3 months 6 months

S1 79.89 79.01

P1 76.50 76.08

S2 71.33 70.00

P2 68.22 67.86

SP1 87.09 86.72

SP2 84.17 83.85

SP3 85.00 84.69

SP4 76.80 76.51

SP5 74.03 74.00

Time (hours) Groups ( % reduction of initial glycaemia )

A B C D E

0 100 100 100 100 100

1 10.05 50.36 11.79 91.97 113.12

3 9.81 16.43 8.97 63.53 116.27

6 16.44 31.62 14.55 87.26 122.09

9 32.169 74.57 25.52 112.35 122.65

12 49.07 75.12 34.526 117.55 122.65

15 58.31 87.57 56.464 121.85 118.05

24 75.39 106.2 77.59 169.5 105.12