Jan 01, 2016
DEFINITIONDEFINITION::Characterization of physical, chemical and mechanical Characterization of physical, chemical and mechanical properties of new drug molecule in order to develop safe, properties of new drug molecule in order to develop safe, effective,and stable dosage form.effective,and stable dosage form.
GOAL OF PREFORMULATION:To formulate an elegant, safe, efficacious dosage form with good bioavailability.To formulate new dosage form of already existing drug.Determination of all the properties of drug and the best suitable dosage form for the drug molecule.
Pharmaceutical factor mainly include those parameters of drug which affect the final dosage form manufacturing process like…..
Flow propertyDensity Compressibility HygroscopicityElectrostatic charge Osmolarity Rheology WettabilitySyringabilty
1)FLOW PROPERTY(A) Introduction Flow property is an important factor that determines the fate of
drug molecule. Sufficient flow is required for uniformity of dosage form. So it
is necessary to judge the flow of material in preformulation stage of the dosage form.
However extreme increase in flow may improve weight uniformity but may reduce content uniformity through increased segregation.
(B) Method of determination By Angle of repose By hopper flow rate By bulk density By angle of spatula By vibrational capillary method
LATEST TECHNOLOGY TO DETERMINE FLOW PROPERTY
REPOSOGRAPH: It is a stable instrument which at best can only indicate
comparative flow properties. The formation of sharp cone would mean poor flow
property while a good spread would indicate a superior flow property.
FT (FREEMAN TECHNOLOGY) RHEOMETER:• An instrument for measuring flow property.• It can discriminate between the samples that differ by 1% Moisture.• Important for optimizing granulation because moisture variation have significant impact on final product quality.
NEW MEASUREMENT SYSTEM TO EVALUATE POWDER FLOWABILITY BASED ON VIBRATIONAL CAPILLARY METHOD:
Evaluates flowability of micrometer sizes particles under actual flow condition.
The amplitude and frequency of vibration is controlled by computer and mass of powder discharged from vibrating capillary tube is measured by digital balance.
The mass flow rate is measured by digital processing.
[Chemical Abstract ,Jan. 2007, 146:9806]
Angle of Repose Indirect method of quantifying powder flowability,because
of their relationship with interparticle cohesion. It is a maximum angle between the surface of a pile of
powder & horizontal plane.
Angle of repose is measured by the equation:
tanθ=h /r
here, h=height of conical heap &
r=radius of horizontal plane of powder
DETERMINATION OF ANGLE OF REPOSEStatic angle of repose Fixed height cone,
Fixed base cone,
Tilting table
Dynamic angle of repose Rotating cylinder
Rotating Drum
Drained angle of repose Ledge type,
Crater type
RELATION BETWEEN ANGLE OF REPOSE & TYPE OF FLOW & TYPE OF
POWDER Angle of
repose Type of flow Type of
powder
<25 Excellent Non cohesive
25-30 Good Non cohesive
30-40 Passable Cohesive
>40 Very poor Very Cohesive
HAUSNER’S RATIO This is a simplex index that can be determined on
small quantities of powder.
Hausner-ratio= Tapped densityβ max)
poured density(Pβ min)
Hausner ratio Type of Flow
<1.25
1.25-1.5
>1.5
Good flow
Moderate
Poor flow
(C) FACTOR AFFECTING FLOW PROPERTY
Particle size and Particle size distribution
Particle shape and Surface roughness
Density and Porosity
Hygroscopicity
Electrostatic charge
(D) IMPROVEMENT OF FLOWABILITY By addition of glidant By addition of fine or by size reduction By wet granulation By removing static charge By densification with the help of slugging Using auger feed equipment By addition of flow activator. Eg. MgO By use silicon treated powder for Hygroscopic &
moist powder. e.g. silicon coated talc or Na-bicarbonate
By altering process condition like vibration assisted hopper or forced feeder
By use of spray drying : Advantose 100 maltose powder has improved flow property than MCC by using this process.
2. DENSITY
(A) INTRODUCTION :The ratio of mass to volume is known as
density. Density = Mass (gms.)/ Volume (ml.)
TYPES OF DENSITY : (a) Bulk density (b)Tapped density (c)True density (d)Granule density :- may affect
compressibility, tablet porosity, disintegration, dissolution
(B) Method of Determination
Parameter Method
1. Bulk density Measuring cylinder
2. Tapped Density Mechanical Device
Mercury Displacement
3. True Density Helium densitometer
(Helium Pycnometer)
Mercury Instrution Porosimetry
Bulk density measurement : It is determined by pouring
presieved (40-mesh) bulk drug into a graduate cylinder via-a large funnel and measuring the volume and weight.
Tapped density measurement:
It is determined by placing a graduated cylinder containing an known mass of drug or formulation on a mechanical tapper apparatus, which is operated for a fixed numbers of taps(about-1000)untill the powder bed volume has reached a minimum.
Measurement of True Density:
True density can be determined using three methods:
displacement of a liquid, displacement of a gas (pycnometry), or floatation in a liquid. The liquid displacement is tedious and
tends to underestimate the true density. Displacement of a gas is more
accurate, but needs relatively expensive instrumentation. Gas pycnometers rely on the measurement of pressure changes, as a reference volume of gas, typically helium, added to, or deleted from, the test cell.
As an alternative, the floatation method is simple to use and inexpensive.
An improved method for fast online measuring of density of solid substances:
A densitometer for measuring of bulk density of solid & liquid consists of one vibrator means, to support pre-weighed samples to be tested in container with predefined shapes on this vibrator & atleast one ultrasonic sensor operatively connected to control unit such that sensor is adapted to transmit and receive reflected ultrasonic pulses to ascertain density of samples utilizing the said values of the fill levels of samples in containers.
(chemical abstract ,October 2007)
(C) CORRELATION WITH FLOWABILITY
Carr’s index = Tapped density- Bulk density/ Tapped density
Hausner ratio = Tapped density / Bulk density
(D) IMPORTANCE In case of combination therapy or physical mixture ,if both
drug or drug & excipients have different density then creates problem of segregation (demixing).
Important in decide size & type of processing equipment. E.g. decide size of capsule formulation, Suppositories.
Devereux et.al. compared GI transit time of multiple unit formulation of densities 2.8g/cm3 & 1.5g/cm3 & found significantly delayed gastric emptying of heavier pdt.
(Review article, IJPS, sept-oct,2008)
3. COMPRESSIBILITY(A) INTRODUCTION
Compressibility is the ability of powder to decrease in volume under pressure.
Neumann and Carr developed a simple test to evaluate flowability of a powder by comparing the poured (fluff) density (Pβmin)and tapped density (Pβmax) of a powder and the rate at which it packed down.
Useful empirical guide is given by the Carr's compressibility index. here compressibility is misnomer since compression is not involved.
%compressibility = Tapped density – bulk density * 100 Tapped density
Relationship between powder flowability and % compressibility
SR. NO % COMPRESSIBILTY RANGE FLOW DESCRIPTIONS
1 5-15 Excellent (free flowing granules)
2 12-16 Good ( free flowing powder granules)
3 18-21 Fair to passable ( powder granules
4 23-28 Poor ( very fluid powder)
5 28-35 Poor ( fluid cohesive powder)
6 35-38 Very poor ( fluid cohesive powder)
7 >40 Extremely poor ( cohesive powder)
(B) The characteristics Of material may be :-
1. PLASTICITY Plastic material are capable of permanent
deformation, also exhibit a degree of brittleness (fragmentability)
But plastic material will get bonding after Viscoelastic deformation.
2. FRAGMENTABILITY If material is fragmentable, neither lubricant
mixing time nor dwell time affecting the tablet strength.
3. ELASTICITY E.g. paracetamol, acetyl salicylic acid
If material is elastic, it rebound when
compression force is released. Elastic material may lead to capping &
lamination They require wet massing to induce plasticity
or plastic tableting material.
4. PUNCH FILMING [STICKING]: This may lead to chipping of tablet.
(C) METHOD OF IMPROVEMENT If plastic material add fragmentable excipient
e.g.. Lactose .
If Elastic material By plastic tableting material Wet granulation ,
Pre compression.
If sticky material By change in salt form, By using high excipient ratio, By wet massing, By addition of Mg-stearate.
NPTAB Technology: Innovative technology combining pellet coating
with direct compression. Active drug is sprayed on carrier containing sugar
sphere & these layered spheres are directly compressed.
“ Multifunctional co-processesed excepients with improved compression properties are used for improved tabletting performance.”
(CHEMICAL ABSTRACT, July 20,2009,151, No.3: 63288g)
4. HYGROSCOPICITY(A) INTRODUCTION Hygroscopicity: - It is the tendency of
material to absorb moisture from atmosphere & be dynamic equilibrium with water in the atmosphere.
Deliquescent: - It is the hygroscopic substance which absorb moisture from air and they can be liquefied by partially or wholly forming solution.
Efflorescent: - a substance which loses water to form a lower hydrate or become anhydrous is term as efflorescent.
List of examples:
Hygroscopic & Deliquescent Efflorescent Ephedrine atropine Hyoscymine cocaine Phenobarbital codeine Pilocarpine scopolamine Physostigmine caffeine
Glycerinated gelatin & PEG base of suppository are hygroscopic in nature.
(B) METHOD OF DETERMINATION
To carry out study, sample of compound are accurately weighed into container and placed at various humid condition for period of upto 2 weeks.
If Weight gain – Deliquescent or Hygroscopic If Weight loss – Efflorescent
Also determined by TGA, GC, & KF titration
Versaperm has deviced a WVTR meter that can measure the permeability of package to moisture in as little as
30 min.so that humidity can be accurately controlled.
(C) IMPORTANCE:
It affects the flow property. It affects compression characteristic ,
granulation & hardness of final tablet. It also affects compaction. Important in aerosol. Affects chemical stability of hydrolysable
drug.
(E) METHODS OF IMPROVEMENT For granulation of hygroscopic material use non-
aqueous solvent. For efflorescent material , use anhydrous salt. Add finely powdered adsorbents like MgO or Mg
carbonate. Perform the entire tableting operation under
controlled humidity condition. Store in desiccant, foil, blister, glass bottle. Use of Ion-exchange resins. Eg. Complexation of Ranitidine with Indion234.
( Journal of Pharmaceutical Research, vol.8.No.2, Apr 2009:112-115)
Examples: Starch is hygroscopic ,but on pregelatinization it exhibits
lower propensity for moisture, thus providing excellent stabilization for moisture sensitive active drugs.
A new multifunctional excipient, Galen IQ.
Problem associated with Hygroscopic material:Stick- slip mechanism of powder flow:
It is pulsatile flow of granular material. It causes problem in die filling for tableting.
“ The length of stick slip event increases with moisture content, increasing load, etc .”
(Chemical Abstract vol.146:9803)
5. ELECTROSTATIC CHARGE
A) INTRODUCTION: Electrostatic charges are the consequence of
classic attraction & repulsion effect between the charges.
Electrostatic charge is produced: By separation of positive & negative charge By mechanical impact By friction between two surface By rupturing of particle By separation of solid & liquid surface
Pharmaceutical processing procedure such as
mixing,micronizing, milling, sieving, rubbing, compressing, spray drying & congealing, pan coating & packaging can induce static charge.
(B) METHOD OF DETERMINATION: INOSTAT, measures negative charge on the
surface in volts/cm, when material is flowing from hopper.
ELPI(13-stage Electrical Low Pressure Impactor), gives detailed charge profile of MDI aerosol particles. This has practical application on lung deposition of MDI aerosol.
Electrostatic testers which consists of electrostatic voltage sensing probes.
C) FACTORS AFFECTING STATIC CHARGE
Effect of particle shape. e.g.- PCM Fine crystalline form >Crystalline form > Granules
with EC > Granules with starch.
Effect of tablet excipient. e.g.- Acetaminophen with mannitol(+++) > SDL(++) > Mg stearate(+)
Effect of Particle size.
Effect of moisture.
(D) IMPORTANCE
In preformulation of suspension . Affects flow property of powder. Affects mixing process. For thermal stability of emulsions. It may damage tablet machine. It may affect compression coating.
E) METHOD OF REMOVAL OF STATIC CHARGE Addition of diluents or lubricant. Surface coating of particle with
amphiphilic substance of o/w type. Eg Aerosol.
Use crystallization method using more polar solvent.
By granulation. Store under influence of air with
sufficient humidity. Super critical fluid technology.
Example: Poloxamer reduce electrostatic charge on the surface of polystyrene.
6. OSMOLARITYA) INTRODUCTION It is a colligative property DEFINITIONS: Osmoles : No. of osmotically active particles in
solution. Osmolarity : osmoles or milliosmoles per liter of
solution. Osmolality :osmoles or milliosmoles per kg of
solvent. Isoosmotic: when two different solutions are
separated by semipermiable membrane have same osmotic pressure so called as isoosmotic.
Isotonic: when two different solutions are separated by biological membrane have same osmotic pressure so called as isotonic.
(B) Method of Determination Osmolality should be measured carefully
with a vapour pressure or freezing point osmometer or cryoscopic osmometer.
Vapour pressure osmometer: Measures concentration of osmotically active particles that reduce V.P of solution.
Membrane osmometer: This invention is directed to a membrane osmometer for direct measurement of osmotic pressures.
( United States Patent 4455864 ) Clifton nanolitre osmometer
(C) IMPORTANCE
Normal serum osmolality to be 285 mosmol/kg.
Maintain osmolarity by 1%variation. It should be proper maintained in
Oral nutrition fluid Peripheral infusion Parenteral product Ophthalmic preparation
Administration of Paratonic solution can lead to crenulation or lysis of RBC.
7. RHEOLOGY
(A) DEFINITION
It describes flow of liquid and/or deformation of solid under stress.
(B) TYPE OF FLOW: Newtonian flow Non Newtonian flow
NEWTONIAN FLOW
It is a flow in which a direct proportionality exists between shear stress and shear rate. E.g. water, simple organic liquid & dilute suspension , Glycerin.
NON NEWTONIAN FLOWWhere there no direct relation between shear stress and shear rate. There are three type
(1) PLASTIC FLOW It is the Newtonian system at shear stress above yield
value. Eg. Flocculated suspension.(2) PSEUDOPLASTIC FLOW Here yield value not associated .As applies shear stress
increasing, viscosity decreases and disarranged molecules begin to align their long axes inline of molecules.
Eg. Aq. Dispersion of tragacanth, Na-CMC, PVP.(3) DILATANT FLOW Opposite to pseudoplastic flow Increase in the shear rate, increasing in resistance to
flow as viscosity increases. E.g. deflocculated suspension of Mg magma
RHEOGRAM
(C) DETERMINATION OF VISCOSITY Capillary viscometer Falling sphere viscometer Cup and bob viscometer Cone and plate viscometer Brook field viscometer Ultrasonic Shear Rheometer :- For analysing
protein solution rheology. Instron Capillary Rheometer :- Measures
viscosity as a function of rate of shear & temp at a high rate of shear.
D)IMPORTANCE
[1] FLUID For mixing For particle size reduction of disperse system Passing though orifice, pouring, packaging in bottle,
passing though hypodermic needle. Flow though pipe Physical stability of disperse system
[2] QUASISOLIDS Spreading and adherence to skin Removal from jar Capacity of solids to mix with liquid Release of drug from base
[3] SOLID Flow of powder from hopper and into a die cavity in
tableting or in encapsulation Packagability of powder or granules solids.
[4] PROCESSING Production capacity of the equipment Processing efficiency
THIXOTROPHY: In thixotropy apply shear stress convert gel – sol &
remove shear stress convert sol – gel, means gel to sol to gel.
Application :- for stability of suspension e.g. conc. Parental suspension containing 40-70% w/v
of procaine penicillin G
8. WETTABILITY
(A) INTRODUCTION Wettability of a solid is an important
property with regards to formulation of solid dosage form.
Adsorption at solid surface is involved in wetting & detergency.
It may influence granulation of solid, penetration of dissolution fluid into tablet and granules & adhesion of coating material to tablet.
(B) METHOD OF DETERMINATION : By contact angle: The contact angle is the angle between a liquid
droplet and the surface over which it spreads. Contact angle – 00 – complete wetting. Contact angle – 1800 – No wetting . By Draves test:
(C) IMPORTANCE: Crystal structure can influence the contact angle. Problems associated with Wettability of powder are
poor dissolution rate & low adhesion of film coating.
(C) IMPROVEMENT Mixing with hydrophilic excipient like Na
CMC (water soluble) and bentonite, Al Mg silicate & colloidal silica (water insoluble).
Use of wetting agent (HLB value 6-9) which acts by lowering contact angle. It displaces air & replace it with liquid phase.
Wetting of powder by non aqueous solvent can be enhanced by certain lanolin derivative.
9. SYRINGABILTY
It is more mechanical property rather than pharmaceutical property.
This phenomenon happens when a liquid dosage form passes through a syringe.
The flow of material is dependant on size & shape of crystals of material.
Plates can easily move one over another .so, no friction observed & can easily pass through the syringe.
While in case of needles or cubes or prisms , they can’t pass through the syringe easily.
So, we can arrange the degree of syringabilty in following way:
Plates > Needles > Cubes > Prisms
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industrial pharmacy ,2nd edition Leon Lachman, H, A. Lieberman, Pharmaceutical dosage form –tablet volume
1 Leon Lachman, H, A. Lieberman, Pharmaceutical dosage form-parental
Dosage form volume 1 Michael E. Aulton, Pharmaceutics: The science of dosage form design ELBS
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