Development and Characterization of Apremilast Transethosomal Gel for Transdermal Delivery

Abstract

The apremilast is anti-inflammatory drug and PDE-4 inhibitor, used in treatment of psoriasis. The oral route of apremilast has limitation of GI irritation and frequent dosage regimen.The objective of the present work was aimed to prepare transethosomal gel of apremilast to achieve more skin permeation, more drug entrapment efficiency and sustained release. The transethosome vesicle containing apremilast was prepared by using Rotary vacuum evaporator, followed by probe sonication. The Box-Behnken design was used to optimize the formulation by taking quantity of lipoid S 100, sodium cholate and ethanol as independent variable and vesicle size, entrapment efficiency and cumulative drug release as dependent variable. The optimized batch of transethosome vesicle was incorporated in 1 % of Carbopol gel base. The prepared optimized batch was evaluated for size, zeta potential, surface morphology, pH, viscosity, spreadability, extrudability, drug content and ex-vivo permeation studies. The result showed that optimized batch of transethosome was found to have vesicle size of 130.8 nm, entrapment efficiency of 62.83 % and cumulative drug release of gel 73.13 %. The transethosome vesicles were found to be spherical and uniform in size based on TEM analysis. The ex-vivo permeation studies were performed for 24 hrs through the rat skin. The formulation was found to show better skin permeation and sustained release. The formulation showed satisfactory result with respect to pH, gel characteristics and stability. Thus, can concluded that transethosomal gel containing apremilast could be an effective option for treatment of psoriasis.

Full text

5508 Int J Pharm Sci Nanotech Vol 14; Issue 3
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Research Paper
Development and Characterization of Apremilast
Transethosomal Gel for Transdermal Delivery
Mrunal Rahangdale* and Prachi Pandey
Babaria Institute of Pharmacy, Gujarat Technological University. BITS Edu Campus, Varnama,
Vadodara, Gujarat, India.
Received February 11, 2021; accepted March 8, 2021
ABSTRACT
The apremilast is anti-inflammatory drug and PDE-4 inhibitor, used
in treatment of psoriasis. The oral route of apremilast has limitation
of GI irritation and frequent dosage regimen.The objective of the
present work was aimed to prepare transethosomal gel of
apremilast to achieve more skin permeation, more drug entrapment
efficiency and sustained release. The transethosome vesicle
containing apremilast was prepared by using Rotary vacuum
evaporator, followed by probe sonication. The Box-Behnken design
was used to optimize the formulation by taking quantity of lipoid
S 100, sodium cholate and ethanol as independent variable and
vesicle size, entrapment efficiency and cumulative drug release as
dependent variable. The optimized batch of transethosome vesicle
was incorporated in 1 % of Carbopol gel base. The prepared
optimized batch was evaluated for size, zeta potential, surface
morphology, pH, viscosity, spreadability, extrudability, drug content
and ex-vivo permeation studies. The result showed that optimized
batch of transethosome was found to have vesicle size of 130.8
nm, entrapment efficiency of 62.83 % and cumulative drug release
of gel 73.13 %. The transethosome vesicles were found to be
spherical and uniform in size based on TEM analysis. The ex-vivo
permeation studies were performed for 24 hrs through the rat skin.
The formulation was found to show better skin permeation and
sustained release. The formulation showed satisfactory result with
respect to pH, gel characteristics and stability. Thus, can concluded
that transethosomal gel containing apremilast could be an effective
option for treatment of psoriasis.
KEYWORDS: Apremilast, Transethosome, Topical drug delivery, Gel.
Introduction
Psoriasis is a chronic inflammatory, autoimmune
disorder. It affects 2-3 % of the total population
worldwide. In India around 2.8 % of the population
suffers from psoriasis. Psoriasis causes rapid build-up of
skin cells this leads to scaling on the skin’s surface. This
event take place deep in the dermis layer of skin. In the
dermis layer inflammation causes the blood vessel to
dilate particularly at the edge of the epidermis and
dermis that delivers more immune cells particularly
neutrophils. The infiltration of the epidermis layer and
dermis layer by the immune cells, triggers the immune
system which in response excrete proinflammatory
cytokines that will maintain and intensify the
inflammatory reaction (Charles, 2004; Lionel 2004).
Thus, the treatment should aim to reduce the
inflammation and drug should penetrate deep into the
skin layers. The topical formulation of anti-inflammatory
drug can be promising treatment (Menter et al., 2007).
Apremilast is a novel, small molecule approved by
FDA in 2014, it has been proved for its clinical safety and
efficacy. Apremilast is an anti-inflammatory drug it is a
phosphodiesterase-4 (PDE-4) inhibitor (Schafer et al.,
2015). It is available in the oral dosage form, the
application of oral drug delivery has numerous problems
such as abdominal pains, upper respiratory,
nasopharyngitis, and depression that often ends in lack
of patient compliance (Afra et al., 2019). It is a class 4
drug, has low solubility and low bioavailability. It
requires frequent dosing regimen, has 72 %
bioavailability and extensive first pass metabolism
occurs. Therefore, to overcome tolerability and frequent
daily dosage and makes better the bioavailability of
APM, an alternative drug delivery is immediately
needed. Thus, a need of topical vesicular delivery seemed
to be more satisfactory (Pradhan et al., 2018).
In recent era topical drug delivery of drug has become
a promising drug delivery system (Lalani et al., 2017).
The vesicular drug delivery is widely explored approach.
These are the drug carriers that carries the drug deep
into the skin and has been found to be an effective drug
delivery (Javia et al., 2018). It has a hydrophilic core
surrounded by lipid bilayer (Bhatt et al., 2018). Thus, it
can incorporate both hydrophilic and hydrophobic drug
molecule (Abdelgawad et al., 2016). The aim of these
system in topical gel is to release the drug for a prolong
period of time and to penetrate in the deep skin layers
without mechanical abrasion. The conventional liposome
was first discovered and explored, later on by modifying
these conventional liposome researchers found out ultra-
deformable vesicles (Arora et al., 2014). The conventional
liposome retains on the top layer of the skin and do not
pass through the stratum corneum; thus, the ultra-
deformable vesicles were designed. The transferosome,
ethosome and transethosome are the deformable vesicles.
International Journal of Pharmaceutical Sciences and Nanotechnology
Volume 14
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https://doi.org/10.37285/ijpsn.2021.14.3.8 MS ID: IJPSN-2-11-21-RAHANGDALE
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Rahangdale and Pandey: Development and Characterization of Apremilast Transethosomal Gel for Transdermal Delivery 5509
The transferosome can deform but cannot permeate deep
into the skin layers. The ethosome contain ethanol due to
which the intercellular space increases and can penetrate
deep into the skin, it fluidizes and lowers the density of
lipid bilayer (Ascenso et al., 2015).
The discovery of transethosome can overcome the
drawback of both vesicles. The transethosome have
qualities of both vesicles of becoming deformable and
penetrates deep into the skin (Song et al., 2012). The
transethosomes are thermodynamically stable, nontoxic
and easy to scale up than other vesicles. Transethosome
are the ultra-deformable vesicle, combination of
ethosome and transferosome has characteristics of both
the vesicles, they easily deform through the pores in the
skin and penetrate deep into the dermis layer. They
possess structure of a hydrophobic and hydrophilic
moiety together, so accommodation of various molecules
of varied range of solubility is possible. They can entrap
low to high molecular weight compound. They are
biodegradable and biocompatible and has high
entrapment efficiency. They are highly stable than other
vesicles (Shaji et al., 2018). The penetration of
transethosome is through transcutaneous hydration
gradient and the presence of ethanol fluidizes the
subcutaneous lipid bilayer. The ethanol disturbs the
skin's lipid bilayer and improves the skin's penetration.
There is hydration force present in the skin also helps
the vesicles to penetrate deep into the skin, the
transethosome follow the naturally occurring energy
gradient called as water activity gradient (Kumar et al.,
2012). Transethosomal gel of Apremilast can provide a
patient compliance, it is a non-invasive method of drug
administration.
Materials and Methods
Materials
Apremilast was obtained as gift sample from Zydus
Cadilla Gujarat, India. Lipoid S 100 obtained as gift
sample from Lipoid (Germany). Sodium cholate from
Chemdyes corporation, India. Ethanol from Udhyogsar-
karimandli Ltd., India. Chloroform and Methanol from
Shree Chalthanvi Bhagkhand Ltd., India. Carbopol 934
from Qualikems fine chem Pvt.Ltd., India. Propylene
glycol from Oxford lab fine chem Ltd., India and
Triethanolamine from Suvidhinath laboratories, India.
Formulation of Transethosomal Gel of a Premilast
Preparation of transethosome vesicles of apremilast:
Transethosomes were formulated by Thin Film
Hydration method (Moolakkadath et al., 2018). In the
round bottom flask, the weighed amount of
apremilast, lipoid S 100 and sodium cholate were
dissolved in volatile organic solution of chloroform and
methanol (2:1). The solution was then evaporated in the
Rotary Vacuum Evaporator (Supertechno Pvt Ltd), kept
at temperature above the transition state of lipid that is
50 ℃ for 1 hr at 90 rpm. This forms the thin layer
deposited on the wall of flask. This deposited layer was
then hydrated with the phosphate buffer pH 6.8, the
flask was rotated mechanically for 1 hr this causes the
vesicles to swell and thus the vesicles are formed but
these are of bigger size. Thus, vesicular dispersion was
subjected to sonication for 4 min using probe sonicator,
Sonics (Vibra cell Pvt. Ltd) to obtain desired size of
vesicles.
The response surface methodology was employed by
using Design Expert ver. 12 software. The experimental
design batches were prepared based on Box Behnken
design and responses were measured. The design was
employed to study the influence of amount of
phospholipid, surfactant and ethanol on dependent
variables such as vesicle size, entrapment efficiency and
drug release. For experimental design the independent
and dependent factors selected are shown in Table 1. The
transethosome vesicles of apremilast were evaluated for
vesicle size, % entrapment efficiency and % cumulative
drug release.
TABLE 1
Independent and dependent variables used in Box-Behnken design
for preparation of Transethosome vesicles of apremilast.
VARIABLES LEVELS
Independent Variables Low Medium High
X 1 Lipoid S 100 (mg) 80 100 120
X 2 Sodium cholate (mg) 10 15 20
X 3 Ethanol (%) 20 30 40
Dependent Variables
Y 1 Vesicle size Minimize
Y 1 Entrapment efficiency Maximize
Y 2 Drug release Maximum drug release
after 8 hrs
Preparation of gel loaded with transethosome
vesicles:
The gel was formulated by dispersing the
Carbopol 934 in warm distilled water with continuous
stirring for 1 hr. The propylene glycol is then added to
the base of the gel and constantly shaken. The 10 ml
solution of transethosomal dispersion is centrifuged at
25,000 rpm for 1 hr at 4℃ in Ultra-centrifuge (REMI
Equipment’s Pvt. Ltd). After centrifugation residues
were collected containing an equivalent amount of 0.1 %
apremilast to prepare 0.1 % of gel and then residues were
dissolved in pH 6.8, this solution was added to the above
prepared Carbopol 934 gel. Then with the
triethanolamine the gel pH was adjusted. Thus, this
forms the Transethosomal gel. The composition of
transethosomal gel is given in Table 2.
TABLE 2
Composition of transethosomal gel.
Ingredients Quantities
Carbopol 934 1 % w/w
Propylene glycol 1 % w/w
Triethanolamine q.s.
Distilled water Up to 100 % w/w
Evaluation Parameters for
Transethosomal Vesicles
Drug and excipients compatibility study:
The
compatibility study was done by taking IR spectra using

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FTIR (Agilent Technologies Cary 630 FTIR) for drug
alone and mixture of drug and excipients (Bhatt et al.,
2020). The physical mixture of drug and screened
excipients Lipoid S 100 and Sodium cholate were
prepared by taking ratio 1:1 after keeping at room
temperature.
Particle size, PDI and zeta potential:
The particle
size, zeta potential and polydispersity index of
transethosome vesicles was analyzed by using Malvern
zeta sizer (Malvern Instruments Ltd) (Yewale et al., 2018).
These parameters describe about the size and
homogeneity of vesicles. The transethosome vesicles was
also observed in the trinocular microscope before
subjecting to the sonication.
Entrapment efficiency:
The vesicular dispersion of
transethosome was subjected to centrifugation, it was
done at speed of 25,000 rpm for 1 hr at 4 ℃ in Ultra-
centrifuge, (Albash et.al, 2019) the obtained supernatant
and residue was analyzed by UV-visible
spectrophotometer (Shimadzu U-1800, Japan).
Finding unentrapped drug concentration:
The
sonicated vesicular dispersion was centrifuged at the
speed of 25,000 rpm for 1hr at 4 ℃ using cooling
centrifuge and obtained supernatant was analyzed by
UV-visible spectrophotometer for determination of
unentrapped drug. The following equation gives the
%Entrapment efficiency:
%EE = (Total drug – Unentrapped drug / Total drug)
× 100
In-Vitro drug release:
The
in-vitro
drug release was
performed using Franz diffusion cell. The dialysis
membrane was used and the receptor chamber was filled
with 20 ml of phosphate buffer pH 6.8, used as diffusion
media in receptor compartment. The receptor medium
was maintained at 37 ± 0.5 ℃ and stirred throughout the
experiment. Aliquots of 5 ml were sampled from the
receptor compartment at interval of 1 hr and then the
same volume of fresh medium was immediately replaced
into the receptor chamber. All samples were analyzed by
UV-visible spectrophotometer for determination of
concentration of drug (Shaji et.al, 2014). Total amount of
drug release at each time interval was calculated and %
cumulative drug release was determined. The release
study was performed for 8 hrs.
Surface morphology determination of transetho-
somes:
Transmission Electron Microscope was used to
study the morphology study of liquid dispersion (Bhatt et
al., 2019). The thin film of vesicular dispersion was
placed on the copper grid which was coated with carbon
and staining was done of the vesicles and they were
observed and photographed.
Characterization of Transethosomal Gel
Organoleptic properties of gel:
The gel formulation
containing transethosome vesicles were investigated
visually for the clarity, colour, appearance and
homogeneity (Abdulbaqi et.al, 2018).
Determination of pH:
pH of topical preparation
should be compatible with the skin pH. pH of gel was
measured by digital pH meter (Toshcon industries Pvt.
Ltd.) calibrated by using standard buffers of pH 4, 7 and
9 before use.
Viscosity:
The physiochemical performance of a gel
gets affected by its rheological properties, it is an
important parameter to be consider. Viscosity of gel was
measured by Brookfield viscometer (Brookfield Pvt. Ltd).
The weighed amount of gel was taken in the beaker. The
T bar 96 spindle was attached to the helipath (LVDV2)
viscometer. The spindle was dipped in the beaker of gel
and was permitted to rotate at room temperature.
Readings were noted from the viscometer dial as the
spindle is rotated at different speed (Lalit Kumar and
Utreja, 2019). Viscosity unit is taken in centipoise.
Spreadability:
The 2 gm of gel was placed on one slide
that was fixed and another slide was placed on it. A
weight of 100 gm was allowed to rest for 5 min on the
upper glass slide. The 20 gm of weight was used to lift
the upper slide. The time taken to travel 6 cm by
movable glass slide to separate it away from the lower
glass slide was noted (Sheikh AA, et.al, 2011). Then,
spreadability was determined using the formula:
S = M.L / T
Where,
S = Spreadability,
M = weight attached to upper slide (20gm)
L = length moved by slide (6cm)
T = time taken (sec)
Drug content:
500 mg of gel was triturated and
diluted with methanol in 50 ml volumetric flask. The
solution was bath sonicated till the clear solution was
obtained. The drug content was determined by
measuring absorbance in UV-visible spectrophoto-meter
where methanol used as blank.
% Drug content =
Actual drug content in vesicles ×100
Th eoret ical wei gh t of dr u g con t e n t i n ves icle s
In-Vitro
drug release: The transethosomal gel was
applied on dialysis membrane on donor compartment of
Franz diffusion cell (Shaji et.al, 2014). The receptor
compartment was filled with 20ml of phosphate buffer
pH 6.8 used as diffusion media in receptor compartment.
The receptor medium was kept at 37 ± 0.5 ℃ and stirred
throughout the experiment. The aliquots were
withdrawn after 1 hr intervals and replaced with
equivalent amount of PBS pH 6.8 and samples were
analyzed by UV spectrophotometer. The release study
was conducted for 8 hrs.
Permeation flux:
Permeation flux is determined by
the slope of percentage cumulative drug release v/s time.
It is expressed in μg/cm2.hr.
Extrudability:
The optimized gel was filled in the
collapsible tube and sealed at the end. The 10 gm of gel
was filled in the tube and tube was placed between two
slides. Weight of 500 gm was placed over the slides and
cap was removed. The extruded gel was collected and
weighed. The percentage of extruded gel was calculated
(Vatset.al, 2012).

Rahangdale and Pandey: Development and Characterization of Apremilast Transethosomal Gel for Transdermal Delivery 5511
Ex-Vivo
drug release study: The
Ex-vivo
drug release
study was performed using Franz diffusion cell using
excised rat skin for duration of 24 hrs. The study was
approved by the IAEC and approval number is
BIP/IAEC/2019/07. The excised skin sample of dorsal
side of 5-6 weeks old rat was mounted on donor
compartment after removing hair. It was clamped on
modified diffusion cell between the donor and receptor
compartment with the stratum corneum facing the donor
chamber. Transethosome vesicles incorporated in gel was
applied on skin on donor compartment. The receptor
compartment was filled with 20 ml of phosphate buffer
pH 6.8 and the receptor medium was maintained at 37 ±
0.5 ℃ and stirred throughout the experiment. After every
1 hr interval, 5 ml aliquots were sampled from the
receptor compartment. The drug release study was
carried out for 8 hrs and % drug in receptor medium was
determined. The % of drug in receptor medium was also
determined at the end of 24 hrs. After 24 hrs the skin
was washed with methanol for finding the amount of
drug present on the skin (Varun, et.al, 2017). Then skin
was homogenized with methanol in homogenizer and
drug retained in skin was also determined.
Stability studies:
The accelerated stability studies
were performed. According to ICH guidelines accelerated
stability study has to be done for new drug product. For
the study, sample was placed at specified storage
conditions of 5 ℃ ± 3 ℃ and accelerated stability condition
at 25 ℃ ± 2℃ & 60 % RH ± 5% RH for 30 days (Abdulbaqi
et.al, 2018). Due to limit of time duration, stability study
was conducted for 30 days. After keeping transethosome
vesicles and gel at above mentioned conditions the batches
were then evaluated for pH, spreadability, extrudability,
viscosity, % cumulative drug release and drug content.
Result and Discussion
Optimization of transethosome vesicles by using Box-
Behnken design.
The formulation optimization was done by Box-
Behnken design by using Design Expert 12 to study the
effect of independent variables on dependent variable
vesicle size (Y1), entrapment efficiency (Y2) and %
cumulative drug release (Y3). The design generated 15
batches having 3 centered point which were then
evaluated for the response’s vesicle size, entrapment
efficiency and cumulative drug release. The responses
were then statistically analyzed by response surface
analysis. From the 3D surface plot, contour plot and
polynomial equation the effect of independent variable on
dependent variable were studied. The design model best
fitted to quadratic model for all the responses. The fit
statistics result showing adjusted R2, predicted R2, S.D.
and %C.V. showed satisfactory result. The result table of
the Box-Behnken design is shown in Table 3 and the
result of fit statistics in shown in Table 4.
TABLE 3
Result table of experimental design batches of Box-Behnken design.
Batch no. Quantity of Lipoid S 100
(mg)
Quantity of Sodium
Cholate (mg)
Quantity of
Ethanol (%)
Vesicle size
(nm)
% Entrapment
Efficiency
% Cumulative
Drug Release
F1 80 20 30 89 43.83 56.24
F2 100 15 30 97 58.49 69.49
F3 120 15 40 169 48.47 57.89
F4 80 15 20 121 56.43 58.14
F5 80 10 30 119 64.52 59.45
F6 100 10 20 127 82.35 75.58
F7 120 15 20 124 73.12 67.91
F8 120 10 30 146 69.93 71.42
F9 80 15 40 134 40.32 44.47
F10 100 10 40 171 55.82 63.87
F11 100 20 40 106 44.27 57.24
F12 100 15 30 96 57.91 66.24
F13 100 20 20 113 56.26 69.44
F14 120 20 30 102 59.54 64.81
F15 100 15 30 99 58.18 67.41
TABLE 4
Result of fit statistics of all responses fitting to quadratic model.
Responses R2 Adjusted R2 Predicted R2 S.D. % C.V.
Y1 0.9917 0.9767 0.8736 4.02 3.35
Y2 0.9956 0.9878 0.9315 1.26 2.17
Y3 0.9918 0.9771 0.9578 1.17 1.85

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Effect of Independent Factors on Response (Y1):
Vesicle size (Y1) = 97.33 + 11.00 A – 20.38 B + 11.88
C + 1.28 AB – 8.00 AC + 12.75 BC + 10.96 A2 + 3.21 B2 +
28.71 C2
Where,
A = Quantity of phospholipid
B = Quantity of surfactant
C = Quantity of ethanol
AB, BC, AC = Interaction between factors
A
2, B2, C2 = Curvatures
Concerning Y1, the results of multiple regression
analysis showed that coefficient A and C bears positive
sign. The sign indicated that as concentration of
phospholipid and ethanol increases Vesicle size also
increases. Whereas, with increase in surfactant the
vesicle size decreases. All variable X1, X2 and X3 shows
effects on vesicle size of formulation. The relationship
between formulation variables and Y1 was further
studied using contour plot and response surface plot as
shown in Figure 1. The contour plot and 3D surface plot
showed same result indicating from the rising trends of
amount of coefficient A vesicle size increases and with
increases in amount of coefficient B vesicle size
decreases.
Fig. 1. Design expert generated graphs of contour plot and 3D plot of vesicle size, % entrapment efficiency and % cumulative drug release.

Rahangdale and Pandey: Development and Characterization of Apremilast Transethosomal Gel for Transdermal Delivery 5513
The effect of Lipoid S 100 was found to be positive as
it can be observed from the Table 3 the vesicle size
increased from 89 nm (F1) to 169 nm (F3) with increase
in lipoid S 100 concentration from 80 mg (F1) to 120 mg
(F2). The same effect was seen for the ethanol vesicle size
increases from 113 nm (F13) to 171 nm (F10) with
increase in ethanol concentration. The negative effect of
sodium cholate was observed the vesicle size decreases
from 171 nm (F10) to 89 nm (F1) with increase in
amount of surfactant, this could be due to the reason that
sodium cholate is anionic in nature this cause the steric
repulsion in the nearby charged molecules which causes
increase in curvature and lessens the size of vesicles.
Effect of Independent Factors on Response (Y2):
% Entrapment efficiency (Y2) = 58.19 + 5.74 A - 8.59
B - 9.90 C + 2.58 AB - 2.14AC + 3.63 BC - 1.91A2 + 3.18
B2 - 1.69 C2
Concerning Y2, the results of multiple regression
analysis showed that coefficient A bears positive sign.
The sign indicated that as concentration of phospholipid
increases % Entrapment efficiency also increases.
Whereas, with increase in surfactant and ethanol the
entrapment efficiency decreases. All variable X1, X2 and
X3 shows effects on Drug entrapment of formulation. The
relationship between formulation variables and Y2 was
further studied using contour plot and response surface
plot, as shown in Figure 1. From the contour plot and 3D
surface plot it can be observed with increasing trending
lines of lipoid S 100 and sodium cholate the entrapment
efficiency increases and decreases respectively.
The effect of Lipoid S 100 can be seen the entrapment
efficiency increases from 40.32% (F9) to 73.12% (F7) as
with increase in amount of phospholipid. This could occur
due to the reason that phospholipid forms more
condensed and compact structure that enables the drug
to get more entrapped in this lipidic region, also the
lipophilic drug can retain more in this region as their
solubility increases. The effect of surfactant on
entrapment efficiency is negative. The decrease of
entrapment efficiency from 82.35% (F6) to 43.83% (F1) is
observed with increase in amount of sodium cholate. This
occurs due to the reason that with decrease in vesicle size
the entrapment efficiency decreases. The effect of ethanol
is observed negative as entrapment efficiency decreases
from 82.35 % (F6) to 40.32 % (F9) with increase in
amount of ethanol. This is causes vesicles to become
leakier with increase in amount of ethanol and drug gets
leaked out of the vesicles.
Effect of Independent Factors on Response (Y3):
% Cumulative Drug Release (Y3) = 67.71 - 5.47 A +
2.82 B + 5.95 C - .85 AB + 0.9125 AC - 0.1225 BC -7.08 A2
+ 2.35 B2 – 3.53 C2
Concerning Y3, the results of regression analysis
showed that coefficient B and C bears positive sign. The
sign indicated that as concentration increases %
cumulative drug release also increases. All variables X1,
X2 and X3 shows effects on % cumulative drug release of
formulation. The relationship between formulation
variables and Y3 was further studied using contour plot
and response surface plot, as shown in Figure 1. From
the contour plot and 3D surface plot it can be observed
with increasing trending lines of sodium cholate the
entrapment efficiency increases and decreases with
increase in lipoid S 100 concentration.
The effect of lipoid S 100 is found to be negative on
cumulative drug release this can be explained from the
condensed structure of vesicle, as the concentration of
lipid increases it forms a compact and condensed
structure that decrease the rate of drug release from the
vesicles. The effect of sodium cholate is positive because
as the vesicle size decreases the surface area increases
and the drug release rate also increases. The ethanol
causes increase in drug release because it causes
fluidization of lipid which makes the vesicles leakier and
hence drug release increases with increase in amount of
ethanol.
Further the optimized batch was prepared by using
the numerical optimizer which works on desirability
function. The desirability function combines all the
responses into one variable to predict the optimum levels
for the independent factors. The optimized batch showing
desirability value near to one was selected as the
optimized batch. The composition of optimized batch
selected was lipoid S 100 (113mg), sodium cholate
(12.14mg) and ethanol (27%). The optimized batch
showed 62.83 % of entrapment efficiency and 73.13 %
cumulative drug release.
Particle size, PDI and Zeta Potential
The optimized batch of vesicle was formulated and
results of the evaluation found were 130.8 nm of particle
size with PDI value 0.212 showing homogenous size
distribution of vesicles, -14.3mV of zeta potential. The
results of particle size and PDI are shown in Figure 2
and zeta potential in Figure 3.
Drug and Excipients Compatibility Study
The FTIR spectra of Apremilast and Sodium cholate
mixture, Apremilast and Lipoid S 100 and Apremilast,
Sodium cholate and Lipoid S 100 mixture taken in ratio
of 1:1 are shown in the Figure 5, 6 and 7 respectively. As
observed in the above FTIR spectra, all the characteristic
peaks of apremilast were present in Drug-Excipient
mixtures, which indicates that there are no interactions
or interference between drug and excipients. So, it can be
concluded that apremilast was compatible with other
excipients used.
Surface Morphology Determination of
Transethosome
Surface morphology of optimized batch of
transethosome vesicles was determined by transmission
electron microscopy (TEM). Results of TEM images are
shown in Figure 8. From the TEM images of
transethosome vesicles it can be observed that vesicles
have spherical structured and size ranged below 200 nm.

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Characterization of Transethosomal Gel
The optimized batch of transethosome was
incorporated in gel and was evaluated for the gel
characteristics. The gel was investigated visually for
organoleptic properties and it was found that gel was
transparent in color, gel was in clear form no particles
were visible and gel showed acceptable homogenous
texture. The result of evaluation of transethosomal gel is
given below in Table 5.
Fig. 2. Particle size of optimized batch of transethosome.
Fig. 3. Zeta potential of optimized batch of transethosome.

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Fig. 4. FTIR spectra of Apremilast
Fig. 5. FTIR spectra of Apremilast and Sodium cholate (1:1)
Fig. 6. FTIR of Apremilast and Lipoid S 100 (1:1).

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Fig. 7. FTIR spectra of Apremilast, Sodium cholate and Lipoid S 100 (1:1).
Fig. 8. TEM images of Transethosome vesicles.
TABLE 5
Evaluation of transethosome incorporated in gel (Optimized batch).
pH Viscosity (cp) at 30 rpm
mean± SD (n=3)
Spreadability (gm.cm/sec)
mean ± SD (n=3)
Drug content (%)
mean± SD (n=3)
Permeation flux (
𝛍
g/cm2/hr)
mean ± SD (n=3)
Extrudability %
mean± SD (n=3)
7.2 18598 ± 0.42 19.15 ± 0.54 96.84 ± 0.63 4.78 ± 0.89 91.73 ± 0.48
From the table it was observed that the results based
on evaluation of pH, spreadability and viscosity of
optimized formulation, it can be said that gel is
compatible with skin and the gel extrude well from the
tube has ease of application. The drug content was also
found to be 96.84%. The permeation flux was also found
to be good the vesicles can permeate well from the skin.
Rheological behavior of gel:
The studies were carried
out using Brookfield helipath, spindle no. 96 and
viscosity of optimized formulation was measured at
increasing RPM and regain in consistency was observed.
Results shown below in Table 6 and Figure 9. The
transethosomal gel showed pseudo plastic behavior. On
application of minimum shear stress, they would thin out
but ones the shear stress is removed they would regain
their normal thickness. Thus, ensures physical integrity
under various stress conditions like manufacturing,
handling and packaging.
Ex-vivo drug release study:
In
Ex-vivo
drug release
study of optimized transethosomal gel was conducted
using Franz diffusion cell with excised rat skin and %
drug permeated through the skin, present in skin and
retained on skin were calculated. Results of
ex-vivo
drug
release study are shown in below Table 7. From the
ex-
vivo
skin retention and permeation study, it was
observed that drug retained inside the rat skin was
higher than compared to drug crossed through the skin
and very less amount of drug was found on the skin
surface. Thus, it can be concluded from the study, that
optimized transethosomal gel of apremilast can retain in
the skin for longer time and is available in the deep skin
layers for inhibiting the proliferation of psoriasis.
TABLE 6
Results of Rheological behavior of gel.
Speed (RPM) Viscosity (cp) ↓ Viscosity (cp) ↑
30 18630 18410
50 10234 10102
100 7884 7627

Rahangd
a
Fig. 9. Pse
u
TABLE 7
Ex-vivo
dr
u
Formu
l
Optimized
b
transethos
o
Stab
il
to be do
n
study w
a
RH for
(Table 8)
viscosity,
drug co
n
conditio
n
storage c
optimize
d
stable u
n
TABLE 8
Results of
s
% CDR
a
pH
V
iscosit
y
Drug co
n
Spread
a
(gm.cm/
s
Extrud
a
Concl
In th
apremila
s
for the
achieve
retentio
n
method
o
rotary v
a
The vesi
c
formulat
i
a
le and Pandey
u
doplastic flow
c
u
g permeation a
n
l
ation
%
b
atch of
o
mal gel
Af
t
38.
5
il
ity studie
s
:
T
n
e for new
d
a
s carried out
30 days. Re
s
that there w
% CDR, s
p
n
tent when
s
n
s (25℃±2℃
&
ondition (5℃
±
d
transethos
o
n
der accelerat
e
s
tability study
Test
B
s
t
t
a
fter 8 hrs
6
y
(cps)
1
n
tent %
9
a
bility
s
ec)
1
a
bility %
9
usions
e present st
u
s
t were prep
a
treatment o
f
high % en
n
and sustai
o
f preparatio
n
a
cuum evapo
r
c
les were th
e
i
on give hom
o
: Developmen
t
c
hart.
n
d skin retentio
n
%
Drug in recepto
r
t
er 8 hrs
A
5
2 ± 0.43 4
4
T
he accelerat
e
d
rug product.
at 25 ℃ ± 2
℃
s
ults of sta
b
as no signific
a
p
readability,
s
tored at th
e
&
60% RH ±
±
3℃) for per
i
o
me formula
t
e
d stability t
e
B
efore
t
ability
t
esting At 5℃ ±
6
8.41 67.8
9
7.2 7.2
1
8431 1824
8
9
4.73 93.8
6
1
9.57 19.2
6
9
1.67 92.1
8
u
dy, the tra
n
a
red and inc
o
f
psoriasis.
T
trapment e
f
n
ed release
n
used was t
h
r
ator followe
d
e
n incorpora
t
o
geneous dist
r
t
and Characte
r
n
studies mean
±
r
medium
A
fter 24 hrs
4
.2 ± 0.32
e
d stability s
t
Accelerated
℃
and 60 %
R
b
ility studies
a
nt change i
n
extrudabilit
y
e
accelerated
5% RH) and
i
od of one m
o
t
ion was fou
n
e
sting.
After 30 days
3℃
Accelerated
c
(25℃ ± 2℃
RH±5%
R
9
66.7
4
7.1
8
1842
6
91.4
3
6
19.4
8
8
91.3
7
n
sethosome
v
o
rporated int
o
T
he purpose
f
ficiency, mo
on applicat
i
h
in film met
h
d
by probe so
t
ed into the
r
ibution of t
h
r
ization of Apr
e
±
SD, n=3
% Drug on the
skin after 24 hrs
3.27 ± 0.16
t
udy has
stability
R
H ± 5 %
showed
n
the pH,
y
and %
storage
specified
o
nth. The
n
d to be
c
ondition
&60%
R
H)
4
1
3
8
7
v
esicle of
o
the gel
was to
re drug
i
on. The
h
od using
nication.
gel. The
h
e vesicle
s
i
w
p
e
a
f
o
F
w
o
d
a
T
s
u
e
T
o
t
o
R
A
A
A
A
A
e
milast Transe
t
% Drug retain
e
skin after
2
51.47 ±
0
i
ze as the P
D
w
ere found to
p
enetrate dee
p
fficiency wa
s
a
mount of dr
u
o
und to be 7
F
rom the
ex-
vi
w
as found mo
r
f the skin,
h
d
isease to elic
i
a
nti-inflamm
a
T
hus, develo
p
u
stained dru
g
ntrapment
a
T
herefore, ap
r
ption for tre
a
o
convention
a
R
eferences
A
bdelgawad R,
N
and systemi
c
Res
8(1): 4-9.
A
bdulbaqi IM,
Transethoso
m
colchicine: st
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evaluation.
D
A
fra TP, Razmi
T
beyond: Big
Online Jour
n
A
lbash R, Abdel
b
transethoso
m
olmesartan
m
Internation
al
A
rora S, Lamba
using differe
n
J
ournal of
P
Asian J Pha
r
t
hosomal Gel f
o
e
d in the
2
4 hrs % D
r
0
.21 1.0
6
D
I value was
fo
have small s
i
p
into the d
e
s
also found
u
g can in ent
r
3.13 % and
s
vi
v
o
studies it
r
e in the der
m
h
ence it is a
v
i
t its action i
a
tory mediato
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p
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s
g
release ch
a
a
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k
r
emilast tran
a
tment of pso
r
a
l form.
N
asr M, Hamza
c
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Darwis Y, Ab
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D
rug design, de
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T
M and Dogra S
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m
n
a
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10(1): 1.
b
ary AA, Refai
m
es for enhan
c
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edoxomil:
in vi
t
al
Journal of Na
n
HS and Tiwari
n
t vesicular ca
r
P
harmaceutics
(
rm
6(4).
o
r Transderma
l
r
ug loss
6
± 0.47
f
ound to be 0.
2
i
ze of 130.8
n
e
rmis layer.
to be highe
r
r
apped. The
d
s
howed sust
a
can be prove
d
m
is layer th
e
v
ailable at t
h
n the dermis
r
s are found i
n
s
t transetho
s
a
racteristic w
k
in permeati
o
sethosomal
g
r
iasis and a
v
MY and Awad
r
s for psoriasis
.
o
uAssi R and
i
ers for the tra
n
z
ation, characte
r
ve
lopment and t
h
(2019). Apremi
l
m
all molecule.
I
H, El-Nabaraw
i
c
ing the trans
d
t
r
o
,
ex vivo
, an
d
n
omedicin
e
14: 1
9
R (2014). Der
m
r
riers: A compa
r
(
AJP): Free fu
ll
l
Delivery
5
2
12. The vesi
c
n
m thus they
The entrap
m
r
62.83 %
m
d
rug release
w
a
in drug rele
a
d
that apremi
l
e
n on the sur
f
h
e genesis of
layer where
n
large numb
e
s
omal gel h
a
ith high %
d
o
n in the s
k
g
el can be be
t
v
iable alterna
t
GA (2016). To
p
.
Int J Curr P
h
Khan NA (2
0
n
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I
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i
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s
d
ermal deliver
y
d
in vivo
evalua
t
9
53.
m
al delivery of d
r
r
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A
ll
text articles
f
5
517
c
les
can
m
ent
m
ore
w
as
a
se.
l
ast
f
ace
the
the
e
rs.
a
s a
d
rug
k
in.
t
ter
t
ive
p
ical
h
arm
0
18).
r
y of
viv
o
and
o
logy
s
e of
y
of
t
ion.
r
ugs
A
sian
f
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Address correspondence to: Mrunal Rahangdale,
Babaria Institute of
Pharmacy, BITS Edu Campus, Varnama, Vadodara.
Tel: 8758391406
E-mail: mrunal651997@gmail.com