EXPERIMENTAL SPTM, SVKM’S, NMIMS, MUMBAI 78 Evaluation Most commonly SMEDDS are evaluated by 142 Thermodynamic Stability Studies: The physical stability of a lipid based formulation is also important to its performance, which can produce adverse effect in the form of precipitation of the drug in the excipient matrix. In addition, the poor physical stability of the formulation can lead to phase separation of the excipient, which affects not only formulation performance, as well as visual appearance of formulation. In addition, incompatibilities between the formulation and the gelatin capsules shell can lead to brittleness or deformation, delayed disintegration, or incomplete release of drug. Thermodynamic stability studies can be conducted by exposing the systems to 1. Heating cooling cycle 2. Centrifugation test 3. Freeze thaw cycle Dispersibility Test The efficiency of self-emulsification of oral nano or micro emulsion is assessed by using a standard USP XXII dissolution apparatus 2 for dispersibility test. One milliliter of each formulation was added in 500 mL of water at 37 ± 1 0 C. A standard stainless steel dissolution paddle is used with rotating speed of 50 rpm provided gentle agitation. The in vitro performance of the formulations is visually assessed using the following grading system Grade A: Rapidly forming (within 1 min) nanoemulsion, having a clear or bluish appearance. Grade B: Rapidly forming, slightly less clear emulsion, having a bluish white appearance. Grade C: Fine milky emulsion that formed within 2 min Grade D: Dull, greyish white emulsion having slightly oily appearance that is slow to emulsify (longer than 2 min). Grade E : Formulation exhibiting either poor or minimal emulsification with large oil globules present on the surface.
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EXPERIMENTAL
SPTM, SVKM’S, NMIMS, MUMBAI 78
Evaluation
Most commonly SMEDDS are evaluated by142
Thermodynamic Stability Studies:
The physical stability of a lipid based formulation is also important to its
performance, which can produce adverse effect in the form of precipitation of the
drug in the excipient matrix. In addition, the poor physical stability of the
formulation can lead to phase separation of the excipient, which affects not
only formulation performance, as well as visual appearance of formulation. In
addition, incompatibilities between the formulation and the gelatin capsules shell
can lead to brittleness or deformation, delayed disintegration, or incomplete release
of drug.
Thermodynamic stability studies can be conducted by exposing the systems to
1. Heating cooling cycle
2. Centrifugation test
3. Freeze thaw cycle
Dispersibility Test
The efficiency of self-emulsification of oral nano or micro emulsion is assessed by
using a standard USP XXII dissolution apparatus 2 for dispersibility test.
One milliliter of each formulation was added in 500 mL of water at 37 ± 1 0C. A
standard stainless steel dissolution paddle is used with rotating speed of 50 rpm
provided gentle agitation. The in vitro performance of the
formulations is visually assessed using the following grading system
Grade A: Rapidly forming (within 1 min) nanoemulsion, having a clear or bluish
appearance.
Grade B: Rapidly forming, slightly less clear emulsion, having a bluish
white appearance.
Grade C: Fine milky emulsion that formed within 2 min
Grade D: Dull, greyish white emulsion having slightly oily appearance that is slow
to emulsify (longer than 2 min).
Grade E : Formulation exhibiting either poor or minimal emulsification with large
oil globules present on the surface.
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Grade A and Grade B formulation will remain as nano- emulsion when dispersed in
GIT. While formulation falling in Grade C could be recommend for SEDDS
formulation.
Turbidimetric Evaluation
Nephelo /turbidimetric evaluation is done to monitor the growth of emulsification.
Fixed quantity of Self- emulsifying system is added to fixed quantity of
suitable medium (0.1N hydrochloric acid) under continuous stirring (50 rpm)
on magnetic hot plate at appropriate temperature, and the increase in turbidity is
measured, by using a turbidimeter. However, since the time required for complete
emulsification is too short, it is not possible to monitor the rate of change of
turbidity (rate of emulsification).
Viscosity Determination
The SEDDS system is generally administered in soft gelatin or hard gelatin
capsules. So, it can be easily pourable into capsules and such systems should not
be too thick. The rheological properties of the micro emulsion are evaluated by
Brookfield viscometer. This viscosities determination conform whether the system
is w/o or o/w. If the system has low viscosity then it is o/w type of the system and if
a high viscosity then it is w/o type of the system.
Droplet Size Analysis and Particle Size Measurements
The droplet size of the emulsions is determined by photon correlation
spectroscopy (which analyses the fluctuations in light scattering due to Brownian
motion of the particles) using a Zetasizer able to measure sizes between 10 and 5000
nm. Light scattering is monitored at 25°C at a 90° angle, after external
standardization with spherical polystyrene beads. The nanometric size range of the
particle is retained even after 100 times dilution with water which proves
the system‟s compatibility with excess water.
Refractive Index and Percent Transmittance
Refractive index and percent transmittance proved the transparency of formulation.
The refractive index of the system is measured by refractometer by putting a drop
of solution on slide and it comparing it with water (1.333). The percent
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transmittance of the system is measured at particular wavelength using UV-
spectrophotometer by using distilled water as blank. If refractive index of system is
similar to the refractive index of water (1.333) and formulation have percent
transmittance > 99 percent, then formulation have transparent nature.
Electro Conductivity Study
The SEDD system contains ionic or non-ionic surfactant, oil, and water. This
test is performed for measurement of the electro conductive nature of system.
The electro conductivity of resultant system is measured by electro conductometer.
In conventional SEDDS, the charge on an oil droplet is negative due to presence of
free fatty acids.
In vitro Diffusion Study
In vitro diffusion studies w e re carried out to study the drug release behavior of
formulation from liquid crystalline phase around the droplet using dialysis
technique.
Drug Content
Drug f r o m pre-weighed SEDDS is extracted by dissolving in suitable
solvent. Drug content in the solvent extract was analyzed by suitable
analytical method against the standard solvent solution of drug.
Zeta potential
The charge of the oil droplets of SMEDDS is another property that should be
assessed.The charge of the oil droplets in conventional SMEDDS is negative due
to the presence of free fatty acids; however, incorporation of a cationic lipid,
such as oleylamine at a concentration range of 1.0-3%, will yield cationic
SMEDDS. Thus, such systems have a positive n-potential value of about 35-45
mV. This positive n-potential value is preserved following the incorporation of the
drug compounds.
Polarity
Emulsion droplet polarity is also a very important factor in characterizing
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emulsification efficiency. The HLB, chain length and degree of unsaturation of the
fatty acid, molecular weight of the hydrophilic portion and concentration of the
emulsifier have an impact on the polarity of the oil droplets. Polarity represents the
affinity of the drug compound for oil and/or water and the type of forces
formed. Rapid release of the drug into the aqueous phase is promoted by polarity.
Drug precipitation /stability on dilution
There are chances of precipitation of drug from SMEDDS upon dilution with
aqueous fluid.143-144
The ability of SMEDDS to maintain the drug in solubilised
form is greatly influenced by the solubility of the drug in oil phase. If the
surfactant or co-surfactant is contributing to the greater extent in drug
solubilisation then there could be a risk of precipitation, as dilution of SMEDDS
will lead to lowering of solvent capacity of the surfactant or co-surfactant, hence it
is very important to determine stability of the system after dilution. This is usually
done by diluting a single dose of SMEDDS in 250 ml of 0.1N HCl solution. This
solution is observed for drug precipitation if any. Ideally SMEDDS should keep the
drug solubilized for four to six hours assuming the gastric retention time of two
hours.
FACTORS AFFECTING SMEDDS
Nature and dose of the drug
Drugs which are administered at very high dose are not suitable for SMEDDS
unless they exhibit extremely good solubility in at least one of the components of
SMEDDS, preferably lipophillic phase. The drugs which exhibit limited solubility in
water and lipids (typically with log P values of approximately 2) are most difficult
to deliver by SMEDDS. The ability of SMEDDS to maintain the drug in
solubilised form is greatly influenced by the solubility of the drug in oil phase.
As mentioned above if surfactant or co-surfactant is contributing to the greater
extent in drug solubilisation then there could be a risk of precipitation, as dilution
of SMEDDS will lead to lowering of solvent capacity of the surfactant or co-
surfactant. Equilibrium solubility measurements can be carried out to anticipate
potential cases of precipitation in the gut. However, crystallisation could be slow
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in the solubilising and colloidal stabilizing environment of the gut. Pouton‟s study
reveal that such formula- tions can take up to five days to reach equilibrium and
that the drug can remain in a super-saturated state for up to 24 hours after the initial
emulsification event. It could thus be argued that such products are not likely to
cause precipitation of the drug in the gut before the drug is absorbed, and indeed
that super-saturation could actually enhance absorption by increasing the
thermodynamic activity of the drug. There is a clear need for practical methods to
predict the fate of drugs after the dispersion of lipid systems in the gastro-intestinal
tract.
Polarity of the lipophillic phase
The polarity of the lipid phase is one of the factors that govern the drug release
from the microemulsions. The polarity of the droplet is governed by the HLB, the
chain length and degree of unsaturation of the fatty acid, the molecular weight of
the hydrophilic portion and the concentration of the emulsifier. In fact, the
polarity reflects the affinity of the drug for oil and/or water, and the type of forces
formed. The high polarity will promote a rapid rate of release of the drug into the
aqueous phase. This is confirmed by the observations of Sang-Cheol Chi, who
observed that the rate of release of idebenone from SMEDDS is dependant upon
the polarity of the oil phase used. The highest release was obtained with the
formulation that had oil phase with highest polarity.
Application
Improvement in Solubility and Bioavailability If drug is formulated in SEDDS, then it increases the solubility
145 because it
circumvents the dissolution step in case of Class-П drug (Low solubility/high
permeability). 146-148
Protection against Biodegradation
The ability of self-emulsifying drug delivery system to reduce degradation as well
as improve absorption may be especially useful for drugs, for which both low
solubility and degradation in the GI tract contribute to a low oral bioavailability.
Many drugs are degraded in physiological system, may be because of acidic PH in
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stomach, hydrolytic degradation, or enzymatic degradation etc. Such drugs when
presented in the form of SEDDS can be well protected against these degradation
processes as liquid crystalline phase in SEDDS might be an act as barrier
between degradating environment and the drug.
4E.2 Literatures review
1. Bok Ki Kang et al in 2004 reported enhancement in bioavailability of
simvastatin by using the technique of self microemulsifying drug delivery
systems. 149
2. Weu Yu et al reported enhanced bioavailability of silymarin by making use of
self microemulsifying drug delivery systems in 2006. 150
3. Ping zhang et al reported improvement in biovailability of oridonin by
preparing slelf microemulsifying drug delivery systems for the same in
2008.151
4. Jong Soo Woo reported reduction in food effect and improvement in
biovailability of itraconazole in 2008.152
5. M.Cirri et al reported development of liquid formulations of xibernol, an
lipopilic drug, by enhancing solubility through formulation of self-micro
emulsifying drug delivery systems in 2007.153
6. Rene holm et al in 2003 and Shui-Mei Khoo et al in 1998, reported
enhancement of in vivo absorption of halofantrine, a poorly soluble
compound by formulating it into self microemulsifying drug delivery system
in 2003. 154-155
7. Patel A.R et al reported improvement in in-vivo absorption of finofibrate by
self microemulsifying drug delivery systems in 2007.156
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4E.3 Materials
Materials used for preparation of SMEDDS were
Table 4E.2 Excipients used for formulation of SMEDDS
Labrafil M 2125 Labrasol
Maisin 35-1
Labrafac PG
Labrafil M 1944
Lauroglycol FCC
Cremophore RH 40
Lauroglycol 90
Cremophore EL
Peceol
Transcutol
Propylene glycol
Polyethylene glycol 400
Isopropyl myristate
Tween 80
4E.4 Solubility studies in modified oils, surfactants and co surfactants
Excess amounts of drug was added to 1gm of modified oils, surfactants and co
surfactants in glass vials .Solution was vortexed for 2 minutes using cyclomixer and
then shaken in rotary shaker for 2 days at 37◦C .Resultant solutions were then
centrifuged for 15 minutes at 2000 rpm. Supernatant was taken diluted suitably with
methanol, filtered through whatmann filter paper 0.45 μm pore size and absorbance
was taken. Each experiment was carried out in triplicate.
4E.5 Preparation of SMEDDS
Based on the results of solubility following combinations of oils,surfactants and co-
surfactants were tried.
Different combinations of surfactant and co-surfactant(S/Cos) were tried in ratios of
surfactant: co-surfactant such as 1:1, 1:2, 1:3, 2:1, 3:1 and 4:1 respectively.
Concentration of oil in s/cos system was varied from 10%-50%.
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Table 4E.3 Combinations for formulation of SMEDDS
Sr.No. Oil Surfactant Co-surfactant
1 Labrafil M 2125 Cremophore RH40 Transcutol
2 Maisin 35-1 Cremophore RH40 Transcutol
3 Labrafil M 1944 Cremophore RH40 Transcutol
4 Labrafil M 2125 Cremophore RH40 PEG 400
5 Maisin 35-1 Cremophore RH40 PEG 400
6 Labrafil M 1944 Cremophore RH40 PEG 400
7 Labrafil M 2125 Cremophore RH40 Ethanol
8 Maisin 35-1 Cremophore RH40 Ethanol
9 Labrafil M 1944 Cremophore RH40 Ethanol
10 Labrafil M 2125 Cremophore EL Transcutol
11 Maisin 35-1 Cremophore EL Transcutol
12 Labrafil M 1944 Cremophore EL Transcutol
13 Labrafil M 2125 Cremophore EL PEG 400
14 Maisin 35-1 Cremophore EL PEG 400
15 Labrafil M 1944 Cremophore EL PEG 400
16 Labrafil M 2125 Cremophore EL Ethanol
17 Maisin 35-1 Cremophore EL Ethanol
18 Labrafil M 1944 Cremophore EL Ethanol
4E.6 Characterization of systems
4E.6 .1 Thermodynamic stability of the systems
A. Heating cooling cycle
Test systems were exposed to six cycles between 4 ˚C and 40˚C with storage at
each temperature was not less than 48 hours.
Systems showing turbidity at the end of test period were discarded. Selected stable
systems were subjected to centrifugation test.
B. Centrifugation test
Test formulations were subjected to centrifugation test by rotating them at 3500
rpm for 30 minutes. Systems which were not showing any phase separation were
tested for freeze –thaw stress test.
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C. Freeze thaw testing
Test formulations were exposed to three cycles of not less than 48 hours at -21º C
and +25ºC. Formulations stable in the testing were considered for further
evaluation.
4E.6 .2 Visual observation of self microemulsifying properties
Method reported by Nazzal et al for visual assessment of self microemulsifying
properties was used with modification.157
Initial screening of self
microemulsifying properties of the systems were judged by dispersing them in
volumetric flask of 50 ml water and adding 0.5 gm of prepared system, time
required for complete dispersion in terms of volumetric flask inversions and
appearance of the dispersion was observed followed by dispersing same amount
of SMEDDS in 900 ml of water in USP type II apparatus at 50 RPM and
maintaining temperature at 37±0.5C.Depending on time required for dispersion
and appearance, systems were classified into following categories-
Grade A-Rapidly forming (within 1 min) nanoemulsion , having a clear or bluish
appearance
Grade B- Rapidly forming (within 1-2 Minutes) nanoemulsion , having a clear or
bluish appearance
Grade C- Nanoemulsion , having a clear or bluish appearance formed in more
than 2 minutes
Grade D-Rapidly forming, slightly less clear emulsion, having a bluish white
appearance
Grade E- Fine milky emulsion that formed within 2 minutes
Grade F – Dull, grayish white emulsion having slightly oily appearance that is
slow to emulsify (longer than 2 minutes)
Grade G- Formulation, exhibiting either poor or minimal emulsification with
large oil globules present on surface.
The formulations that passed stability and also dispersibility test in grade A were
selected for further studies.
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4E.6 .3 Pseudoternary phase diagram
Pseudo ternary phase diagrams of oil ,surfactant /cosurfactant ratio (s/cos), and
water were developed using the water titration method.The mixtures of oil and
s/cos at certain weight ratios were diluted with water in a dropwise manner.158
For each phase diagram , selected mixtures were titrated with water and visually
observed for phase clarity .Boundaries of self microemulsifying region of the
selected systems was found out by noting the amount of water required for
transparent to turbid and turbid to transparent transitions of the given systems.
Phase diagrams were constructed using chemix ternary phase diagram software.