SUMMARY. The present study addresses the solubility issue of a hydrophobic antifungal drug and its incorporation into a hydrogel matrix. The prime objective of the study was to develop a preformed hydrogel of 1% w/w clotrimazole with the introduction of water miscible co-solvents such as glycerin and polyethylene glycol. Carbomer was used as gelling agent in different concentrations. The stability of the formulations, their spreadability, pH, drug content, viscosity and in vitro drug release has been assessed while the optimization has been carried out through Design Expert® ver. 7.0. A spectrophotometric method has been developed for the analysis of clotrimazole from the developed formulations and it was found to be within the USP limits. The best drug release was found from F2 formulation that contains 0.5 g carbomer hence it was considered as optimized formulation. It is conclu

1. 675
KEY WORDS: carbomer, clotrimazole, hydrogel, in vitro release.
* Author to whom correspondence should be addressed. E-mail: iyadnaeem@uok.edu.pk
Latin American Journal of Pharmacy
(formerly Acta Farmacéutica Bonaerense)
Lat. Am. J. Pharm. 37 (4): 675-81 (2018)
Received: October 19, 2017
Revised version: February 23, 2018
Accepted: February 25, 2018
Development and Pharmaceutical Evaluation of Clotrimazole
Loaded Topical Hydrogel Formulation
Aatka ALI, Iyad N. MUHAMMAD*, S. M. FARID HASAN & Madiha MUSHTAQUE
Department of Pharmaceutics, Faculty of Pharmacy,
University of Karachi, Karachi, Pakistan
SUMMARY. The present study addresses the solubility issue of a hydrophobic antifungal drug and its in-
corporation into a hydrogel matrix. The prime objective of the study was to develop a preformed hydrogel
of 1% w/w clotrimazole with the introduction of water miscible co-solvents such as glycerin and polyethy-
lene glycol. Carbomer was used as gelling agent in different concentrations. The stability of the formula-
tions, their spreadability, pH, drug content, viscosity and in vitro drug release has been assessed while the
optimization has been carried out through Design Expert® ver. 7.0. A spectrophotometric method has
been developed for the analysis of clotrimazole from the developed formulations and it was found to be
within the USP limits. The best drug release was found from F2 formulation that contains 0.5 g carbomer
hence it was considered as optimized formulation. It is concluded that hydrogel of clotrimazole can be suc-
cessfully prepared by introducing co-solvency phenomenon.
RESUMEN. El presente estudio se refiere a la solubilidad de un fármaco antifúngico hidrofóbico y su incorpora-
ción a una matriz de hidrogel. El objetivo principal del estudio fue desarrollar un hidrogel preformado de clotri-
mazol al 1% p/p con la introducción de codisolventes miscibles en agua tales como glicerina y polietilenglicol.
El carbómero se usó como agente gelificante en diferentes concentraciones. Se ha evaluado la estabilidad de las
formulaciones, su extensibilidad, pH, contenido de fármaco, viscosidad y liberación de fármaco in vitro, mientras
que la optimización se ha llevado a cabo a través de Design Expert® ver. 7.0. Se ha desarrollado un método es-
pectrofotométrico para el análisis de clotrimazol a partir de las formulaciones desarrolladas y se encontró que es-
taba dentro de los límites de la USP. La mejor liberación de fármaco se encontró a partir de la formulación F2
que contiene 0,5 g de carbómero, por lo que se consideró como una formulación optimizada. Se concluye que el
hidrogel de clotrimazol puede prepararse con éxito mediante la introducción del fenómeno de co-solvencia.
INTRODUCTION
Hydrogels are cross-linked three dimensional
networks composed of water-soluble polymers.
The conventional application of hydrogels is to
deliver small molecule hydrophilic drugs. In
such networks, the loading of a large quantity
of hydrophilic drug into swollen hydrogel is
comparatively easier than hydrophobic drug.
The introduction of hydrophobic drug in a hy-
drogel-based formulation is a challenging task
in various aspects since it inherits incompatibili-
ty issues between a hydrophobic drug and the
hydrophilic hydrogel network 1. In order to cir-
cumvent the problem, the aqueous solubility of
a drug can be enhanced by co-solvency, hy-
drotropism, complex formation, ionization and
inclusion of surfactants 2. The phenomenon of
co-solvency is often used to augment the solu-
bility of poor water soluble drugs in liquid
preparations. Co-solvent system lowers the in-
terfacial tension between the hydrophobic so-
lute and the aqueous solution 3. Clotrimazole
has been used as a model drug in the present
study since it belongs to BCS class II. It is not
merely an antifungal agent but also acts against
sickle cell anemia, malaria, beriberi, chagas dis-
ease and cancer 4. The main objective of the
present study was to develop a stable hydrogel
formulation of clotrimazole with the aid of co-
solvents.
ISSN 0326 2383 (printed ed.)
ISSN 2362-3853 (on line ed.)

2. 676
ALI A., MUHAMMAD I.N., FARID HASAN S.M. & MUSHTAQUE M.
Up till now, there are lots of studies carried
out on the hydroalcholic gel formulation of
clotrimazole. Gel formulations developed with
alcoholic content are not frequently used nowa-
days. They have potential to cause rapid dry-
ness and irritation. In contrast, high water con-
tent hydrogel has been prepared without incor-
poration of acetone, alcohol or any other harsh
solvents 5. Therefore, the present study has
been carried out with the objective to design a
topical hydrogel formulation without an intro-
duction of alcoholic solvents that would be
more suitable in terms of patient compliance.
MATERIALS AND METHODS
Materials
Clotrimazole was provided as a gift sample
by Bayer Pakistan (Pvt.) Ltd. Karachi, Pakistan.
Carbomer 934 was obtained from Avonchem,
Cheshire, United Kingdom. Sodium hydroxide
pellets were purchased from Merck KGaA,
Darmstadt, Germany. Glycerol and Methyl-4-hy-
droxybenzoate (methyl paraben) were obtained
from BDH laboratory supplies, Poole, England.
Polyethylene glycol (PEG) 400 and ethanol were
purchased from Sigma Aldrich, Steinheims, Ger-
many. Whatman grade no.41 filter paper (Schle-
icher & Schuell, Maidstone, England) was used
for filtration purpose. Distillation assembly
(Hamitton Laboratories, Kent, England) was
used to purify water.
Rationale for the formulation of hydrogel
The formulations were composed statistically
using a single factor general factorial design of
experiments through Design expert® (Stat-Ease,
Inc. USA version 7.0, 2005) (Table 1). The soft-
ware was used for the optimization on the basis
of the results of assay and in vitro release keep-
ing the polymer at three concentrations (levels)
i.e. 0.25 to 1%.
Ingredients F1 (%w/w) F2 (%w/w) F3 (%w/w)
Clotrimazole 1 1 1
Carbomer 934 0.25 0.5 1
NaOH (10%) Qs* Qs* Qs*
Glycerol 10 10 10
PEG 400 5 5 5
Methyl paraben 0.1 0.1 0.1
Distilled water Qs* Qs* Qs*
Table 1. Composition of clotrimazole hydrogel formulations. *Qs = quantity sufficient for 100 g.
Preparation of hydrogel
Accurately weighed carbomer 934 on analyti-
cal balance (Sartorius, Göttingen, Germany) and
then dispersed in distilled water using magnetic
stirrer (Jenway 1000, Chelmsford, England) for
two hours at 100 rpm. The resultant dispersion
was converted into gel base by neutralization
with 10% NaOH w/w. Clotrimazole was dissolved
in viscous mixture of PEG 400, glycerol and
methyl paraben. This viscous solution was thor-
oughly mixed into the viscous carbomer gel base
with sufficient addition of distilled water to make
100 g of gel. This method was selected after some
modification as reported by Baviskar et al. 6.
Physicochemical evaluation
The pH of the formulations was determined
using glass electrode attached to a digital pH
meter (Jenway 370, Chelmsford, England).
Spreadability of formulations was determined by
marking a circle of 2 cm diameter in the middle
of the glass plate and then 0.5 g gel was em-
ployed over it. Another plate with 500 g weight
was permitted to place over the first plate and
then the diameter of the circle was measured af-
ter 5 min 7. Brookfield DV II Pro viscometer
(MA, USA) with RVT-TD spindle was rotated at
10 rpm in order to measure the viscosity of the
formulations. Organoleptic characteristics of all
the formulations were assessed. As per Interna-
tional Conference on Harmonization (ICH)
guidelines, selected gel formulations were kept
in accelerated stability chamber at 40 °C and
75% relative humidity for six months 8.
Method development and validation for the
analysis of clotrimazole
A UV spectrometric method was developed
and validated for the determination of clotrima-
zole using double beam UV-visible spectropho-
tometer (1800, Shimadzu, Kyoto, Japan).

3. 677
Stock and test solutions preparation
A stock solution having 1% concentration of clotrimazole was prepared in ethanol. It was further
diluted to obtain a second stock of 2000 µg/mL concentration. From this second stock solution, test
solutions in the concentration range of 80-240 µg/mL were prepared.
Validation of the developed method
Parameters of validation such as linearity, accuracy, precision, limit of detection and limit of
quantification were assessed according to ICH guidelines 9. In order to ascertain linearity, five con-
centrations of standard were processed in triplicate and the calibration curve was constructed. The
accuracy of the method was determined by the addition of known concentrations of analyte in the
solution. The validation parameters such as limit of detection (LOD), limit of quantification (LOQ), %
Relative standard deviation (RSD) and recovery were calculated from Eqs. [1-4]
Equation Kinetic model Plotted graph
C = k0 t a Zero order Cumulative % drug release vs. time
logC = logC0 – kt / 2.303 b
First order
Log cumulative % drug remaining
to be release vs. time
Q = kH √t c Higuchi model Cumulative % drug release vs. √t
Table 2. Kinetic models and the plotted graph. a C = Drug concentration at time t, k0= Zero order rate constant.
b C0 = Initial concentration at time t, k = First order rate constant. c Q = Drug release amount at time t, kH =
Higuchi release rate constant.
LOD = (3.3 × SD of intercept) / Slope [1]
LOQ = (10 × SD of intercept)/slope [2]
% Relative standard deviation =SD / Mean ×100 [3]
Recovery (%) = (Amount found)/ (Amount added) × 100 [4]
Assay of clotrimazole
Drug content was determined by weighing 1
g of the gel equivalent to 10 mg of clotrimazole,
properly mixed with 25 mL of ethanol prior to
filtration. The absorbance was measured on UV-
visible spectrophotometer at 260 nm using
ethanol as a blank reagent in order to correct
baseline.
In vitro release testing
The release characteristics of drug from the
formulations were assessed by using a digital 6-
cell diffusion apparatus accompanied with ther-
mostat water circulation tank (EMFDC 06, Or-
chid scientific, Nashik, India). Hydroalcholic so-
lution (50:50 v/v) was used as medium to fill
the receptor compartments of each diffusion cell
having capacity of about 5 mL 10. It was contin-
uously stirred with the help of magnetic bead at
100 rpm and 32 ± 0.5 °C. Nylon membranes
(Membrane Solutions, USA) having 1.69 cm2
surface area and 0.45 µm pore size were kept
soak in the receptor medium for 30 min before
mounting between the two compartments of the
diffusion cell. In the donor compartments, about
200 mg of gel was placed over the membrane
and covered with the aid of parafilm to avoid
vehicle evaporation. The samples were taken
out and replenished with an equal quantity of
fresh receptor medium up to 1 h. The samples
were analyzed by developed validated method.
Analysis of release profile
Zero order, first-order and Higuchi model
were applied on the data obtained from the in
vitro release studies 11,12 (Table 2). Linear regres-
sion analysis was carried out for all the kinetic
models.
RESULTS AND DISCUSSION
Topical hydrogel formulations of clotrima-
zole have been developed and optimized suc-
cessfully. Optimization of the formulations
through Design Expert® software is illustrated
in Figs. 1 and 2.
It is reported in literature that poor water
soluble drugs can be dispersed in gel but in cer-
tain cases, hydrophilic water miscible co-sol-
Latin American Journal of Pharmacy - 37 (4): 675-81 (2018)

4. 678
ALI A., MUHAMMAD I.N., FARID HASAN S.M. & MUSHTAQUE M.
vents such as PEG and glycerin can be used to
solubilized insoluble drugs 13. Hydrophilic water
miscible co-solvents have been added in the
present study to overcome the solubility issue of
clotrimazole in the gel base. The effect on the
carbomer polymeric system with the introduc-
tion of hydrophilic solvents such as PEG 400
and glycerin has been previously reported in lit-
erature 14. In the present work, carbomer con-
centration was kept variable in order to assess
their effects on the viscosity of aqueous neutral-
ized carbomer gel samples in presence of hy-
drophilic solvents. A hydroalcholic gel of clotri-
mazole had been prepared with the same poly-
mer 15 but in the present study the co-solvency
phenomenon has been introduced to prepare
pure hydrogel instead of hydroalcoholic gel.
Physicochemical characterization
The pH of the formulations F2 and F3 were
found to be 6.6 ± 0.07 and 6.1 ± 0.4 respective-
ly. The pH has been adjusted between 6.1-6.6 in
order to match with the acceptable physiologi-
cal pH. Lambers et al. reported the variable pH
of skin but all values lies between the acidic
ranges i.e. 4.0 to 7.0 16. It has been revealed in
one of the previous studies that clotrimazole re-
tained its stability at or above pH 6.0 17. Mitta-
palli et al. 18 reported the degradation of clotri-
mazole in highly acidic or basic media. It has al-
so been reported in one of the study that two
degraded entities i.e. imidazole ring and (2-
chlorophenyl) diphenyl methanol are produced
as a result of acid degradation of clotrimazole 19.
Figure 1. Optimization through software on the basis
of assay results of gel formulations.
Figure 2. Formulations optimization through software
based on in vitro release.
Figure 3. Clotrimazole hydrogel formulation (F2).
Therefore, in the present study, pH has been
adjusted above 6.0 with the aid of 10% NaOH
w/w solution.
The developed hydrogel formulations were
white in color however formulation coded F2
showed less opaque color due to low polymer
content (Figs. 3 and 4).
Formulation F1 could not maintained gel like
consistency. Therefore, it was not further evalu-
ated for physicochemical characteristics. The
viscosities of F2 and F3 formulation were found
to be 2.4 × 105 ± 0.3 cP and 4.8 × 105 ± 0.1 cP,
respectively. It is evident that higher polymer
content in formulation F3 leads to higher viscos-
ity as compared to formulation F2. In contrast,
the spreadability of formulation F2 was more
(7.56 ± 0.20 cm) than formulation F3 (5.13 ±

5. 679
0.15 cm). It is indicated that higher polymer
concentration imposes a negative effect on
spreadability.
Development and validation of assay
method
The developed method showed linearity in
concentration range of 80-240 µg/mL with good
correlation coefficient (r2) i.e. 0.9997. The accu-
racy of the method was 98.97 ± 0.93 whereas
the percent recoveries of the method were
found to be 98.41-100.63%. The LOD and LOQ
of the developed method were found to be
17.184 and 52.074 µg/mL, respectively. The re-
sults of intra-day precision at three different
time intervals and inter-day precision on three
consecutive days are shown in Table 3. The
overlay UV spectra showing λmax at 260 nm are
illustrated in Fig. 5.
Assay of clotrimazole
The assay results of clotrimazole from the
developed analytical method were found to be
within USP specification i.e. not less than 90.0%
and not more than 110.0% 20. The drug content
from F2 formulation was found to be 98.9 ±
Figure 4. Clotrimazole hydrogel formulation (F3).
Intra-day Precision Inter-day Precision
8:30 1:00 5:00 Mean ± RSD b 1st 2nd 3rd Mean ± RSD
am pm pm SD a (%) day day day SD (%)
80 79.75 81.0 78.9 79.9 ± 0.84 1.06 77.8 78.4 79.7 78.65 ± 0.9 1.26
120 117.9 120.1 120.0 119.3 ± 1.2 1.03 120.2 119.4 117.9 119.1 ± 1.16 0.97
160 159 158 158.3 158.4 ± 0.51 0.32 156.6 162.7 159 159.43 ± 3.0 1.90
Table 3. Intra-day and inter-day variability for three different concentrations of clotrimazole. a SD = Standard de-
viation, b RSD = Relative standard deviation.
Figure 5. Overlay spectra of clotrimazole.
Figure 6. In vitro release profiles of the developed
formulations.
Standard
concentration
(µg/mL)
0.46% whereas 100.3 ± 0.71% was obtained
from F3 formulation. Software generated Fig. 1
shown F2 as optimized formulation on the basis
of desirable assay.
In vitro release profile of clotrimazole
Formulation F2 selected as optimized formu-
lation on the basis of drug release profile as evi-
dent in Fig. 6 and Fig. 2. Formulation F2 and F3
exhibited 97% and 85% drug release respective-
Latin American Journal of Pharmacy - 37 (4): 675-81 (2018)

6. 680
ALI A., MUHAMMAD I.N., FARID HASAN S.M. & MUSHTAQUE M.
ly at 1 hr. The results revealed that drug diffuses
rapidly from F2 formulation that has lower poly-
mer concentration. The regression coefficient
values corresponding to each kinetic model are
shown in Table 4. The higher r2 value indicated
that release data could be best fitted on Higuchi
model in which the release of drug is propor-
tional to the square root of time.
Accelerated stability studies
The physicochemical properties throughout
the study period including viscosity, pH and
spreadability were found to be maintained in
closed glass container. There is no appreciable
change in pH, spreadability, viscosity and drug
content has been observed as shown in Table 5.
It revealed that there is no any incompatibili-
ty issues associated with a hydrophilic polymer
(carbomer) and a hydrophobic drug (clotrima-
zole). Moreover, the six months accelerated sta-
bility study also showed that water miscible co-
solvent system does not disturb the gelling
property of carbomer and the studied evaluation
parameters remains constant.
F2 formulation
Model r2 Slope
Zero order 0.958 94.52
First order 0.915 3.32
Higuchi model 0.990 97.41
F3 formulation
Zero order 0.970 84.4
First order 0.935 1.9
Higuchi model 0.978 85.89
Table 4. Parameters of release kinetic models.
Time Formulation
pH
Spreadability Viscosity × 105 Assay
(months) Code (cm) (cP) (%)
0
F2 6.63 ± 0.05 7.56 ± 0.20 2.4 ± 0.25 98.9 ± 0.46
F3 6.10 ± 0.1 5.13 ± 0.15 4.8 ± 0.1 100.3 ± 0.71
1
F2 6.62 ± 0.05 7.58 ± 0.1 2.4 ± 0.9 99.06 ± 0.46
F3 6.11 ± 0.2 5.10 ± 0.2 4.8 ± 0.08 98.59 ± 0.46
3
F2 6.60 ± 0.06 7.66 ± 0.3 2.4 ± 0.69 99.05 ± 0.46
F3 6.12 ± 0.09 5.00 ± 0.2 4.8 ± 0.09 98.9 ± 0.71
6
F2 6.63 ± 0.1 7.68 ± 0.09 2.4 ± 0.9 98.4 ± 0.26
F3 6.11 ± 0.3 5.00 ± 0.2 4.8 ± 0.89 98.5 ± 0.25
Table 5. Accelerated stability data of studied evaluation parameters. Mean ± standard deviation, n = 3.
CONCLUSION
It is concluded that co solvency is a suitable
phenomenon for the incorporation of clotrima-
zole into hydrogel. It further proved that alco-
holic content is not necessary to overcome the
solubility issue of hydrophobic drug. Co sol-
vents are sufficient to prepare a hydrogel de-
void of any harsh solvents that may lead to irri-
tation. Carbomer served as a gelling agent, was
found to be compatible with co solvents. The
developed method does not require overnight
soaking of polymer hence it is time saving. It
has scale up tendency and it can be more
adaptable to the patient therefore further clinical
study is required.
Acknowledgement. The authors are highly grateful
to Dr. Iqbal Ahmed and Dr. Muhammad Ali Sheraz of
Baqai Institute of Pharmaceutical Sciences, Baqai
Medical University, Karachi, Pakistan for their kind
support.
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