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Original Research Paper

Organogels, hydrogels and bigels as transdermal deliverysystems for diltiazem hydrochloride

Mahmoud Mokhtar Ibrahim a,b,*, Salma A. Hafez a, Mahmoud M. Mahdy a

aDepartment of Pharmaceutics, Faculty of pharmacy, Zagazig University, Zagazig, EgyptbDepartment of Pharmaceutics, Faculty of Pharmacy, Najran University, Najran, Saudi Arabia

a r t i c l e i n f o

Article history:

Received 16 January 2013

Received in revised form

10 February 2013

Accepted 15 February 2013

Keywords:

Organogels

Hydrogels

Bigels

Lecithin

Span

* Corresponding author. Department of PharmE-mail address: mahmoud_dsky@zu.edu.egPeer review under responsibility of Shenyan

Production and hosting by El

1818-0876/$ e see front matter ª 2013 Shenyhttp://dx.doi.org/10.1016/j.ajps.2013.07.006

a b s t r a c t

In the present study, gel formulations of organogels, hydrogels, and oleo-hydrogel (bigels)

wereevaluatedas transdermaldrugdelivery systems fordiltiazemHCL (DH).Organogelswere

preparedusingsoya-beanoil (SO)asasolventandspan60 (Sp60), cetylalcohol (CA)or lecithin-

pluronic (PLO)asorganogelatorswithoutandwithdifferentsurfactants (2%w/w)namelyspan

80 (Sp80), tween 20 (T20) and tween 80 (T80). On the other hand, hydrogels were formulated

using Hydroxypropyl-methylcellulose (HPMC) polymer and bigels were prepared by mixing

organogels with HPMC hydrogels. The prepared gels were analyzed microscopically, ther-

mally by DTA and for pH, and viscosity. The effect of gelator used, surfactant types and pH of

the sink on DH release from cellophane membrane was investigated. In addition, the DH

permeability across the rabbit skinwas evaluated. Finally, the in vivo performance of various

gel formulationswasassessedbasedonthehypotensiveeffectsof thedrugusinghypertensive

albino male rat models. The microscopical analysis indicated that the solid fibers formed by

gelator particles form the backbone of the organogelswhile bigels appeared as emulsion like.

Theadditionof surfactantsshowedan increase inorganogelviscosity. Thethermalanalysisof

organogels indicated that the drug present in amorphous not in crystalline form. The release

studies indicated that DH release from organogels, hydrogels and bigels could be controlled.

The included surfactants decreased the DH release and permeation from organogels

compared to those without surfactants using either Sp60 or CA. HPMC hydrogel and Bigels

showed higher DH release and permeation rates when compared to organogels. The percent

DH released in different pH values was in the following descending order:

pH5.5>pH1.2>pH6.8>pH7.4. The in vivo antihypertensive activity of DH using different

transdermalgels isarrangedas following:hydrogels>PLOorganogel>bigel>Sp60organogel.

ª 2013 Shenyang Pharmaceutical University. Production and hosting by Elsevier B.V. All

rights reserved.

aceutics, Faculty of pharmacy, Zagazig University, Zagazig, Egypt. Tel.: þ20 552303266.(M.M. Ibrahim).g Pharmaceutical University

sevier

ang Pharmaceutical University. Production and hosting by Elsevier B.V. All rights reserved.

a s i a n j o u rn a l o f p h a rm a c e u t i c a l s c i e n c e s 8 ( 2 0 1 3 ) 4 8e5 7 49

1. Introduction stabilizers that makes gelation feasible with lecithin of a

The development of new drug molecules is time consuming

and expensive. On the other hand, the existing marketed and

patented drug substances with known therapeutic effects can

be used with the modification of their pharmacotherapeutic

characteristics. This was achieved by incorporating the drug

in a suitable drug delivery system [1]. Diltiazem HCl (DH) is a

calcium channel blocker belonging to the benzothiazepine

family. It is widely prescribed for the treatment of hyperten-

sion and angina [2]. Although DH is well absorbed from the

gastrointestinal tract, it undergoes substantial hepatic first-

pass effect. Therefore, DH elimination half-life is very short

(3e4.5 h) and frequent administration of the drug required to

maintain therapeutic effect. The drug dosage is reported to be

30 mg 4 times a day and may increase as necessary up to

360 mg/day in divided doses in order to maintain adequate

plasma levels [3]. Transdermal application of the drugwas our

target of this investigation to minimize the frequency of DH

administration and overcome its side effects after oral

administration of conventional dosage forms.

The transdermal route of drug administration is definitely

one of the potential routes for local and systemic delivery.

This route provides a controlled diffusion of drugs into the

systemic circulation, breaksmany barriers in medical therapy

like the need of assistance, intermediate dosing and uncom-

fortable administration and improves patient compliance

[4,5]. In general, gel-based products may be categorized either

as hydrogels or organogels depending on the polarity of the

external liquid component. Water is the external liquid

component of hydrogels while organogels were formulated

using non-polar solvents such as hexane, isopropyl myristate,

sunflower oil, corn oil or others.

Hydrogels are prepared using natural or synthetic hy-

drophilic polymers which form a colloidal network of

polymer chains in water. They possess a degree of flexibility

which is very similar to natural tissue. Moreover, hydrogels

are of many uses such as essential controlled drug delivery

systems, in cell culture, dressing for healing of wounds.

Their easy way of preparation and availability made them of

high value in the pharmaceutical field [6]. On the other

hand, the use of organogel based products is increasing due

to their easy method of preparation and inherent long-term

stability [7]. Depending on the mechanism of the formation

of the three dimensional gel skeleton, the organogels are

considered as fluid-filled structures and solid-fiber based

gels [8]. They are thermoreversible and have the ability to

accommodate both hydrophilic and hydrophobic com-

pounds within the gel structure. This property has also

widened the scope of the organogels uses as controlled drug

delivery systems which can be taken via several routes of

administration. The gelators which compose the major

skeleton of an organogel are generally amphiphilic sub-

stances, such as sorbitan monostearate (Sp60) and sorbitan

monopalmitate (Sp40). Moreover, Lecithin organogels can be

obtained by the addition of a critical amount of water to its

non-aqueous solutions [9]. Recent reports have also sug-

gested the incorporation of synthetic polymers (e.g. Plur-

onics) into Lecithin organogels as cosurfactants and

relative lower purity. The formulation has referred to as

Pluronic lecithin organogels (PLOs) [10]. Oleogel/hydrogel

mixtures (bigels) were also synthesized as topical formula-

tions based on mixing hydrogels (aqueous systems) with

oleogels (lipophilic systems) [11]. The aim of the present

investigation was to enhance the transdermal permeability

of the highly water soluble drug DH. Different gel types

namely hydrogels, organogels and bigels were formulated

and subjected to in vitro evaluation. The drug hypotensive

effects were also assessed after transdermal application of

DH gels on hypertensive rat models.

2. Materials and methods

2.1. Materials

Diltiazem HCl (DH) was a gift from Egyptian Pharmaceutical

industrial company (E.P.I.Co), Egypt. Sp60, Sp80, T20, T80, CA,

Pluronic F127, HPMC, and SO were purchased from Sigma

chemical Co., St. Louis, MO, USA. The Epikuron 200 phospho-

lipids (>92% SPC) were a gift from Lucas Meyer, Hamburg, Ger-

many. All other chemicals were of analytical grades and

obtained from the El-Nasr Company for pharmaceutical chem-

icals, Cairo, Egypt.

2.2. Gels preparation

Different organogels, hydrogels and bigels were prepared by

different procedures which are briefly described below and

the formulations are listed in Table 1. The final DH concen-

tration was adjusted to be 150 mg/g in all the formulations.

2.2.1. OrganogelsOrganogels were prepared by dissolving 10% w/w of Sp60 or

CA in SO vehicle into the SO in wide mouth vials, without or

with additional 2% w/w of different surfactants such as Sp80,

T20 or T80. The vials were kept in a water bath at 60 �C, until ahomogenous clear solution was obtained. The hot solutions

were allowed to cool down at room temperature so as to allow

organogel formation.

150 mg of DH was loaded into each 1 g of the organogel

formulations by the mixing 0.2 ml of heated DH (60 �C) solu-tion (750 mg/ml) in distilled water with the surfactant hot oily

solution while magnetic stirring at 500 rpm. The mixture was

allowed to cool giving the medicated organogel formulas [12].

2.2.2. PLO gelsThe aqueous phase (10% w/w Pluronic F127 solution in water)

of PLO was prepared by the cold process reported by Murdan

[10]. PLO gels were obtained by adding the oil phase (solution

of PC in SO) to the aqueous phase with vigorous stirring. The

hydrophilic DH solution was added to the aqueous phase with

stirring before the addition of the oil phase [10].

2.2.3. HydrogelsHPMC hydrogels were prepared by allowing the weighed

quantities of HPMC (10% w/w) to be soaked in distilled water

Table 1 e Composition and proportion of different gel formulation.

Formulation Concentration of various compositions (w/w) (Total weight ¼ 10 g)

Sp60(g)

CA(g)

Sp80(g)

T20(g)

T80(g)

Lecithin(g)

Pluronic(g)

HPMC(g)

SO(g)

Water(g)

DH Solution(750 mg/ml)

Sp60/SO organogel 1 e e e e e e e 7 e 2

Sp60/Sp80 orgaanogel 1 e 0.2 e e e e e 6.8 e 2

Sp60/T20 organogel 1 e e 0.2 e e e e 6.8 e 2

Sp60/T80 organogel 1 e e e 0.2 e e e 6.8 e 2

CA/SO organogel e 1 e e e e e e 7 e 2

CA/Sp80 organogel e 1 0.2 e e e e e 6.8 e 2

CA/T20 organogel e 1 e 0.2 e e e e 6.8 e 2

CA/T80 organogel e 1 e e 0.2 e e e 6.8 e 2

PLO e e e e e 1 0.5 e 4 2.5 2

HPMC hydrogel e e e e e e e 1 e 7 2

Sp60/HPMC bigel 0.5 e e e e e e 0.5 2.5 4.5 2

Sp60/Sp80/HPMC bigel 0.5 e 0.1 e e e e 0.5 2.4 4.5 2

Sp60/T20/HPMC bigel 0.5 e e 0.1 e e e 0.5 2.4 4.5 2

Sp60/T80/HPMC bigel 0.5 e e e 0.1 e e 0.5 2.4 4.5 2

CA/HPMC bigel e 0.5 e e e e e 0.5 2.5 4.5 2

CA/Sp80/HPMC bigel e 0.5 0.1 e e e e 0.5 2.4 4.5 2

CA/T80/HPMC bigel e 0.5 e e 0.1 e e 0.5 2.4 4.5 2

a s i a n j o u rn a l o f p h a rma c e u t i c a l s c i e n c e s 8 ( 2 0 1 3 ) 4 8e5 750

for a period of 2 h until complete hydration and gel formation.

DH solution (750 mg/ml) was added to the dispersions with

continuous stirring until homogenous gel was formed and the

drug concentration was adjusted to be 150 mg/1 g.

2.2.4. BigelsThe prepared gels were stored separately at 4 �C for at least

24 h, then bigels were prepared by mixing HPMC hydrogels

with the Sp60 or CA organogels (1:1 w/w) prepared without or

with different surfactants.

2.3. Microscopic study

A compound optical microscope (Olympus B 41) was used for

analyzing the microstructure of the organogel, hydrogel and

bigels. Attempts were used to understand the mechanism of

the gel formation by varying the composition and proportion

of the ingredients used and analyzing their microstructure.

2.4. Thermal analysis

Thermal properties of organogels were studied using differ-

entials thermal analysis (TA-50 thermal analyzer, Shimadzu,

Japan). Samples were heated from 0 �C up to 600 �C, at a rate of

6 �C/min.

2.5. pH measurement

The pH of the organogel, hydrogel and bigel samples was

detected by using digital pH meter (Cole-parmer instrument

Co., U.S.A). The pH of the gels was measured by bringing the

probe of the pH meter in contact with the sample [13].

2.6. Determination of viscosity

The viscosity of all the gel formulations was determined by

using Visco Star-R FUNGILAB viscometer, sample spindle (R6)

and speed of 10 rpm at 25 �C. The value of the viscosity is

displayed in the form of cP.

2.7. In vitro release study

In vitro release of DH from different gel formulations was per-

formed using shaker water bath (Serve well Instruments and

Equipment, Pvt. Ltd. India) maintained at temperature of

32 �C� 1 �Candallowed toagitate at 50 rpm.Onegramof thegel

was weighed in plastic holders then attached to a permeation

cell previously specified by Mahmoud et al. and covered with

the cellophane membrane (soaked in phosphate buffer pH 5.5

for 24 h before use) [14]. The cell was immersed to the depth of

1 cm below the surface of the phosphate buffer (pH 5.5) in the

receptor compartment (50 ml). Samples of 3 ml each from the

receptor compartment was taken at various time intervals of

15, 30, 60, 120, 180, 240, 300 and 360 min and assayed for DH at

237 nm using UVeVisible Spectrophotometer (Shimadzu-UV-

1201, Japan). To maintain sink condition, the sample volume

was replacedwith equal volume of the fresh buffermaintained

at 32 �C. Each experiment was carried out in triplicate.

2.8. In vitro skin permeation studies

Abdominal skin of male rabbits (2e2.5 kg) was used in this

study. Before the permeation study, the skin was hydrated in

phosphate buffer pH 5.5 at 4 �C overnight and the adipose

tissue layer of the skin was removed by rubbing with a cotton

swab [15]. The permeation experiments were run by using the

same cells previously described in the in vitro release studies

but the abdominal rabbit skin rather than semi-permeable

cellophane membrane was used to cover the gel preparation

with the stratum corneum side face [16]. The experiment was

continued as described above. The cumulative amount of DH

permeated per unit surface area was plotted vs. time.

2.9. In vivo study of DH as transdermally appliedantihypertensive agent

This study was done using adult albino male rats weighing

250e300 g obtained from the animal breading center, Faculty

a s i a n j o u rn a l o f p h a rm a c e u t i c a l s c i e n c e s 8 ( 2 0 1 3 ) 4 8e5 7 51

of Veterinary medicine, Zagazig University, Egypt. Animals

were treated according to Ethical committee of animal

handling in Zagazig University “ECAHZU”. Firstly, hyperten-

sion was induced in rats by complete left renal artery ligation

according to the method described by Cangiano et al. [17].

Postoperatively, the rats were given penicillin G (100,000 units

I.M.) per rat for three successive days, and were allowed free

access to food and water for 28 days till the complete induc-

tion of hypertension [18]. In vivo studies were done using DH

formulations of Sp60/SO organogel, HPMC hydrogel, PLO and

Sp60/HPMC bigel to evaluate their antihypertensive effects

when administered transdermally. Results were compared

with that of the non treated rats as negative controls and

those administered oral DH solution as positive controls.

Animals were divided into six groups as listed in Table 2. Each

group consisting of six rats (n ¼ 6) and allowed the application

of 0.2 g of different gel formulationswhich containing 30mg of

DH on the hairless skin of the abdomen region (about 4 cm2 in

size). The negative control group was received placebo

hydrogel free from drug. The positive control group (300 g

weighed rats) received the dose of 0.027ml of oral DH solution

which containing 2.025 mg of DH.

The oral dose calculated according to Paget’s equation [19]:

The therapeutic dose for rat weighing 200 g

¼ 18�Adult human therapeutic dose ð75 mgÞ1000

¼ 1:35 mg

On the other hand, according to Fick’s first low, the drug

efflux increased across the skin as the concentration gradient

increased [20]. To reach the maximum thermodynamic ac-

tivity, the drug concentration in the donor compartment

applied transdermally must be maximum or in the saturation

state. Accordingly, DH concentration in the transdermal gels

to be tested was kept as high as possible (30 mg/0.2 g gel).

The blood pressure measurements were done using

Oscillograph (Washington, 400 MD 4C, Bio Science, Sheerness,

Kent, U.K) at time intervals from 0 to 6 h. The rats were

anaesthetized with urethane (ethyl carbamate) in a dose of

1.75e2.0 g/kg body weight then injected I.P as 25% freshly

prepared aqueous solution. Intra arterial cannulation was

done and the systemic arterial blood pressure was recorded

and the blood pressure of rats was determined employing the

method of Burden et al. [21].

Table 2 e Classification of in vivo transdermal and oralgroups.

Groups Formulation

Group (I) Control and received placebo gels

free from drug (�ve control).

Group (II) Received 0.2 g of Sp60/SO organogel

which containing 30 mg of DH.

roup (III) Received 0.2 g PLO about which

containing 30 mg of DH.

Group (IV) Received 0.2 g of SP60/HPMC bigel

which containing 30 mg of DH.

Group (V) Received 0.2 g of HPMC hydrogel

which containing 30 mg of DH.

Group (VI) Received 0.027 g of oral solution

which containing 2.025 mg of DH (þve control)

The antihypertensive effects of the selected formulations

were studied after induction of hypertension into rats and the

results were compared to that of the control (group I). For

in vivo performance, gels which showed the highest release

rates both through the cellophane membrane and the

permeability across rabbit skin were selected. The antihy-

pertensive activitywas studied at different time intervals after

application (1, 2, 3, 4, 5 and 6 h) to differentiate between the

onset of action of the oral DH solution and transdermal gel

formulations. The mean arterial blood pressure was calcu-

lated according to the following equation [22]:

Mean arterial B:P ¼ Diastolic B:P

þ ðSystolic B:P�Diastolic B:PÞ3

2.10. Statistical analysis

All values were expressed as mean � SD. Data were analyzed

statistically using one way analysis of variance (ANOVA) test.

The level of significance was considered at P < 0.05.

3. Results and discussion

Different organogelators were dissolved in the hot oil phase

until a clear homogenous solution was obtained. As the tem-

perature cooleddown, thegelatorsprecipitated in theoil due to

changes in the solubility parameters. The precipitated gelators

grown insizeasfibersor reverse cylindricalmicelles.Thefibers

or the micelles physically entangled with each other to form a

threedimensionalnetworkedstructure [23]. Thegel containers

were then inverted and observed for any flow (Fig. 1). Samples

were considered as organogels if they did not flow [12]. All the

preparedgels except thoseof the PLOwerewhite to pale yellow

in color, oily in touch, opaque in nature and no odor.

Concerning PLO, it was jelly like in appearance with yellow

color, and aqueous touch. On the other hand, the prepared DH

hydrogel was transparent, homogenous, clear and smooth

with aqueous touch because the liquid compartment is water.

In addition, bigels (combined forms of hydrogels with orga-

nogels) were white in color, creamy in appearance with ho-

mogenous smooth non oily touch. It is well known that a large

number of emulsifiers could affect the properties of lamellar

lipids of the intracellular matrix of the SC, resulting in the

increased transepidermal water loss and several irritant re-

actions [24]. However, the simple composition of organogels,

bigels and hydrogels is therefore beneficial considering the

safety of these formulations.

3.1. Gel morphology

The variations in the microstructure of organogels were

studied as the gelator and/or surfactant types changed (Fig. 2).

The results showed the presence of needle shaped clusters of

Sp60 when 10% (w/w) gelator concentration was used (Fig. 2).

As another surfactant added such as T80, T20, or Sp80, these

clusters aggregated to form fiber-like structures. These fiber-

like structures were in the form of networked skeleton

which could help in the immobilization of the oil. Hydrogel

Fig. 1 e Gelation process of the organogel (a) Clear solution after heating; (b) Uniform, cloudy suspension upon cooling and

standing; (c) Opaque, semi-solid gel upon further standing.

a s i a n j o u rn a l o f p h a rma c e u t i c a l s c i e n c e s 8 ( 2 0 1 3 ) 4 8e5 752

showed Blank pictures where bigels appeared emulsion like

with the oil phase dispersed in a continuous aqueous one.

3.2. Thermal analysis

The thermogram of DH showed a single sharp endothermic

peak at 207.55 �C and another broad one at 245.50 �C(Fig. 3(a)). The sharp endothermic peak is corresponding to

the melting point of the drug where the broad one is cor-

responding to its decomposition [25]. Also, Fig. 3 (b and c)

showed strong endothermic peaks at 48.78 �C and 50.93 �Cwhich indicated the melting points of CA and Sp60,

respectively. DTA-thermogram of DH-CA organogel showed

a small and broad peak of DH appeared at 208 �C (Fig. 3(d)).

However, Sp60-DH organogel showed shifting of DH peak

from 207 �C to 188 �C and become smaller than that of pure

Fig. 2 e Microscopic study of different gel formulations, a) Sp60/

microstructure of bigel.

DH. This indicated the interaction of the gel clusters of Sp60

and DH which pointed to the presence of the drug in the

amorphous nature (Fig. 3(e)). These results agree with that

of Sultana et al., who found that the endothermic peak of

DH in alginate microspheres was not distinctive indicating

that, the drug was no longer present in the crystalline

form [26].

3.3. Measurements of the gel pH and viscosity

The pH values of the organogels, hydrogels and bigels were

found to be in the range of 4.66e5.91 (Table 3), which were

close to skin pH 4.5e7 [27]. This enhances a safe application to

the skinwithout irritation problems. All gel formulationswere

found to have viscosities in the range of 870 cP to 34900 cP, and

as a general observation, the incorporation of surfactants

SO organogel. b) Sp60/Sp80 organogel. c) HPMC hydrogel. d)

Fig. 3 e Thermal analysis, a) Pure DH, b) Pure CA, c) Pure

Sp60, d) DH-CA organogel and e) DH-Sp60 organogel.

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50

60

70

0 50 100 150 200 250 300 350 400

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% D

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CASp 60Lecithin/Pluronic

Fig. 4 e Effect of different organogelators on DH release.

a s i a n j o u rn a l o f p h a rm a c e u t i c a l s c i e n c e s 8 ( 2 0 1 3 ) 4 8e5 7 53

such as T80, T20, or Sp80 resulted in increasing the viscosity of

the gel as listed in Table 3.

3.4. In vitro release of DH across semi-permeablecellophane membrane (pH 5.5)

For transdermal drug delivery, in vitro drug release tests are

often performed before transdermal permeation studies.

From the in vitro release studies it is possible to determine how

the viscosity and the ingredients of the vehicle affected the

drug release profiles of each formulation [28]. The release of

DH from organogels of SO formulated using different gelling

agents is demonstrated in Fig. 4. From Fig. 4, it is clearly

illustrated that DH was slowly released from organogels

where different gelators used. About 43.7%, 49.4, and 50.4% of

the drug was released after 360 min from organogels of the

PLO, Sp60, and CA gelators, respectively. The drug release was

dependent on the solid skeleton network formed by the

gelator molecules [29,30]. CA and Sp60 organogels exhibited a

similar drug release pattern (no significant difference; P> 0.05)

due to the similarity in their transition temperatures (about

Table 3 e The pH and viscosity values of various gelformulations.

Formulation Viscosity (cP) pH

Sp60/SO organogel 1000 5.61 � 0.32

Sp60/Sp80 orgaanogel 1800 5.29 � 0.21

Sp60/T20 organogel 8000 4.98 � 0.15

Sp60/T80 organogel 32,100 5.11 � 0.40

CA/SO organogel 3400 5.04 � 0.30

CA/Sp80 organogel 7000 4.98 � 0.15

CA/T20 organogel 7200 4.85 � 0.13

CA/T80 organogel 7400 4.90 � 0.18

PLO 1900 4.66 � 0.19

HPMC hydrogel 870 5.66 � 0.33

Sp60/HPMC bigel 14,400 5.87 � 0.40

Sp60/Sp80/HPMC bigel 9900 5.66 � 0.17

Sp60/T20/HPMC bigel 27,000 5.14 � 0.30

Sp60/T80/HPMC bigel 34,900 5.23 � 0.15

CA/HPMC bigel 14,900 5.91 � 0.23

CA/Sp80/HPMC bigel 8900 5.82 � 0.18

CA/T80/HPMC bigel 15,900 5.15 � 0.12

50.93 �C and 48.78 �C for Sp60 and CA, respectively). Con-

cerning PLO, the significant lower DH release rate may be

attributed to the high affinity between the freely water soluble

DH and PLO surfactants concentrated on the emulsion inter-

face. A similar study showed the release of 81.56% piroxicam

at 48 h from PLO organogels, however the solubility of pirox-

icam in water was low [30]. The authors attributed the result

to the amphiphilic nature of pluronic and the weak affinity

between pluronic and piroxicam which may facilitate the

release of poor water soluble drugs from organogels.

Inclusion of surface active agents into gels is well known to

affect drug release and permeability across biological mem-

branes [31]. Different surfactants of different acyl chain

lengths and unsaturation such as Sp80, T20 or T80 were used

in concentrations of 2% w/w to modify the release profile of

DH from the organogels of Sp60/SO or CA/SO. From Fig. 5(a

and b), it was observed that the percentage DH released after

360 min from different organogels containing 2% of Sp80, T20,

or T80 were 38.48%, 33.80%, and 27.56%, respectively with

Sp60/SO organogels and was 44.21%, 40.04% and 39.52%,

respectively with CA/SO organogels. Generally, all surfactants

had significantly decreased the drug release (P < 0.05) from

organogels compared to those without surfactants in both

Sp60 and CA. This result might be due to the participated in-

verse tubular aggregation of Sp60 or CA that increased the

viscosity and gel strength [32]. On the other hand, incorpora-

tion of Sp80 into organogels resulted in a significant higher DH

release rate when compared to Tween incorporated gels for

both Sp60 and CA organogels. The result might be due to the

high degree of lipophilicity of spans compared to Tweens and

this could lead to lower affinities to hydrophilic drugs [33]. The

viscosity of the prepared gel might be another reason for the

deviations recorded in drug release rates from different gels.

The viscosity of organogels containing Sp80was found too low

when compared to those containing T80 or T20. Moreover, the

lower DH release from organogels containing Tween surfac-

tants may be ascribed to the longer fiber length of Tween

surfactant which can cause an increased area of overlap and

cross-linking, producing high gel strengths [30]. T20 has a

comparatively lower gel-strengthening effect and showed

higher fluxes than T80 [32]. The active participation of Tweens

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dHPMC hydrogelSp60Sp60/2%Sp80Sp60/2%T20Sp60/2%T80

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HPMC hydrogelCACA/2% sp 80CA/2%T20CA/2% T80

c d

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Sp60/HPMCSp60/Sp80/HPMCSp60/T20/HPMCSp60/T80/HPMC

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CA/HPMCCA/Sp80/HPMCCA/T80/HPMC

a b

Fig. 5 e Release profiles of DH from different vehicles. (a) Sp60 organogels vs. HPMC gel, (b) CA organogels vs. HPMC gel, (c)

Bigels of Sp60, and (d) Bigels of CA.

a s i a n j o u rn a l o f p h a rma c e u t i c a l s c i e n c e s 8 ( 2 0 1 3 ) 4 8e5 754

in micelle formation produced an increased area of micellar

overlapmight be the reason for linear increase in the viscosity

of the organogel [34].

The release of DH from HPMC hydrogel was also included

in this study and compared with organogels. The percentage

DH released from HPMC hydrogel was 55.64% after 360 min as

shown in Fig. 5 (a and b). The hydrogels are three dimensional

polymeric networks with chemical or physical cross links

which can control the drug delivery via controlling the base

viscosity [35]. The amount of DH released from hydrogels of

HPMC was higher than that from all organogels. This may be

due to the aqueous liquid component of hydrogels which can

impede large amount of water or biological fluid [35]. On the

other hand, organogels has a liquid organic (lipophilic) me-

dium which make the release of freely water soluble drug

more difficult.

Several formulations of bigels prepared by using different

organogels of Sp60 or CA with SO with or without different

surfactants (Sp80, T20 or T80) andmixedwith HPMC hydrogel.

From Fig. 5(c), it was illustrated that the percentage DH

released after 360 min from different bigels of Sp60/HPMC,

Sp60/Sp80/HPMC, Sp60/T20/HPMC and Sp60/T80/HPMC were

59.80%, 55.12%, 48.36% and 46.28%, respectively. While,

72.28%, 54.60% and 41.08% of DH were released from bigels of

CA/HPMC, CA/Sp80/HPMC and CA/T80/HPMC, respectively as

shown in Fig. 5(d). It is clear that all bigels gave significantly

higher release rates than organogels (P < 0.05). This may be

attributed to the fact that organogels are W/O type emulsions

having an external lipid phase [11], while a bigel is a w/o/w

type emulsion due to the incorporation of the organogel inside

the hydrogel which have an external aqueous phase and

capable of incorporating large amounts of water [35]. The

hydrophilic nature of the external aqueous environment of a

bigel facilitates the release of the hydrophilic drug from the

external aqueous phase. The release would be faster for a

hydrophilic drug in case of o/w emulsion, since it is in the

continuum region. The diffusion is difficult when DH incor-

porated in w/o type emulsion base, since it gets trapped in

water droplets. The reverse is true for hydrophobic drugs [36].

To show the effect of the pH of the external sink on DH

release, CA/SO organogel and CA/HPMC bigel were formulated

and tested for DH release in different pH values. Fig. 6(a)

showed that the percentage DH released from CA/SO orga-

nogel and CA/HPMC bigel after 360 min was 50.4 and 72.28%

when pH was 5.5, 33.80% and 51.48% at pH 1.2, 24.96% and

32.68% at pH 6.8, and 14.66% and 18.09% at pH 7.4, respec-

tively. The amount of DH released in different pH values was

in the following descending order: pH 5.5 > pH 1.2 > pH

6.8 > pH 7.4. Diltiazem is a basic drug and should be more

soluble in the acidic media than neutral and alkaline media.

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200 250 300 350 400

Time (min)

% D

iltia

zem

Hcl

rel

ease

dCA/HPMC (pH 5.5)CA organogel (pH 5.5)CA/HPMC (pH 1.2)CA organogel (pH 1.2)CA/HPMC (pH 6.8)CA organogel (pH 6.8)CA/HPMC (pH 7.4)CA organogel (pH 7.4)

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 50 100 150 200 250 300 350 400

Time (min)

Am

ount

DH

per

mea

ted

(µg/

cm2 )

HPMC hydrogelPLOSp60/HPMCCA/HPMCSp60/SOCA/SO

a b

Fig. 6 e (a) represents the release of DH from CA organogels and bigels in different pH values and (b) represents the

permeation of DH from hydrogel, PLO, bigel and organogel formulations across Rabbit skin.

a s i a n j o u rn a l o f p h a rm a c e u t i c a l s c i e n c e s 8 ( 2 0 1 3 ) 4 8e5 7 55

However, the decline in the DH solubility in HCl buffer pH 1.2

was attributed to the common ion effect, which provided

unexpected trend in solubility of this medicament in the

presence of chloride ion in the medium [37]. On the other

hand, high amounts of DH were released in pH 5.5 which in

turn were gradually decreased at pH 6.8 and 7.4. The result

might be due to the acidic nature of DH salt of a basic drug

having pka of 7.7 and the molecule is freely soluble in water.

The high the release profile of DH can be attributed to rapid

ionization and higher solubility of the drug in pH 5.5, however

the reduced release rate of DH in pH 7.4 could be due to the

reduced the extent of ionization and solubility of DH in basic

media [37].

3.5. In vitro rabbit skin permeation study

The aim of this study was to examine the possibility of using

organogels, hydrogels and bigels as transdermal delivery forms.

Fig. 6(b) shows the cumulative amount of DH expressed in mg/

cm2 transferred from different gel formulations to the receptor

compartment (phosphate buffer pH 5.5). Throughout the

experiment period, the hydrogel of HPMC showed higher

amount of DH skin permeability than other organogel formu-

lations. After 360 min, about 1569.50, 1286.28, 1121.07, 1062.0,

979.46 and 483.83 mg/cm2 of DH were permeated across rabbit

skin from HPMC hydrogel, PLO, Sp60/HPMC bigel, CA/HPMC

bigel, Sp60/SO and CA/SO organogel formulations, respectively.

Firstly, it must be taken into consideration that the partitioning

of a drug between the skin and the reservoir favors more lipo-

philic drug because skin act as an organic phase [38]. Skin is a

horny layer so penetration of drugs is very less. To improve the

penetration of a drug into the skin, chemical enhancers are

added. Incorporation of HPMC enhances the flux of drugs [39].

Hydrogel consists of an aqueous phase which facilitates the

penetration of hydrophilic drug. Also, lower gel viscosity might

be another reason for higher amount of DH permeated the

rabbit skin using hydrogels of DH. Concerning PLO organogel,

the amount of DH permeatedwas higher than Sp60/SO and CA/

SO organogels due to the aqueous external compartment and

the amphiphilic nature of phospholipids which can enhance

skin penetration and absorption of both lipophilic and hydro-

philic drugs [40]. The phospholipid tail ofmicelles could interact

with the lipids in SC causing their rearrangement and thus

facilitated drug penetration between epidermal cells into sys-

temic circulation [41]. Also, bigels of Sp60/HPMC and CA/HPMC

gave higher penetration rates than their organogels and this

could be as discussed before due to the external aqueous phase

of bigel as well as the surfactant activity of CA and Sp60. CA/SO

organogel gave the lowest fluxes which may be ascribed to its

lower surface activity and higher viscosity (3400 cP) when

compared to Sp60/SO organogel (1000 cP).

3.6. In vivo study of DH

Fig. 7 shows the significant decrease in the mean arterial blood

pressure in all hypertensive rats receiving transdermal DH gels

compared to the group I (�ve control) at all time intervals. The

one way ANOVA test revealed that the difference between the

antihypertensive effects of DH in all transdermal groups was

statistically significant (P < 0.05) when compared to control

group at all time intervals of the experiment. Group VI which

received oral doses of DH solution showed a sharp decrease in

blood pressure after 1 h (92 mmHg) then gradually increased

after the fourth hour. A statistical significant difference

(P < 0.05) was found between oral solution group and all

transdermal groups during the first 2 h. Meanwhile, no statis-

tical significance (P > 0.05) was observed after 3 h till the end of

the experiment between transdermally applied organogels,

bigels and oral DH solution. On the other hand, group V which

received HPMC hydrogel showed a statistical significant dif-

ference (P< 0.05) comparedwith oral solution group after 4 h till

the end of the experiment. This result may be attributed to the

0

20

40

60

80

100

120

140

160

180

0 2 4 6Time (h)

Mea

n ar

teri

al B

.P (

mm

Hg)

ControlSp60/SO organogelPLOSp60/HPMC bigelHPMC hydrogelDH oral solution

Fig. 7 e Meanarterial blood pressure of rat groups received

different DH gel formulations via the transdermal route

compared with non treated group and those taken DH

solution via the oral route. Data represented as mean ± SD

(n [ 6).

a s i a n j o u rn a l o f p h a rma c e u t i c a l s c i e n c e s 8 ( 2 0 1 3 ) 4 8e5 756

fact that the hydrogel gives faster antihypertensive effect when

compared with other transdermal groups as it decreased the

blood pressure gradually andmaintained it. From these results

all transdermal gels can give comparable results to oral solution

and reveal a sustained antihypertensive effect. A statistical

significant difference (P< 0.05) between group V (hydrogel) and

group II (Sp60 organogel) was observed at all times of the

experiment. However, groups III (PLO) and IV (bigel) showed no

statistical difference (P > 0.05) at all times of experiment. The

results which obtained with all transdermal groups revealed

that, the antihypertensive effects of DH could be arranged in

the following order: hydrogel > PLO > bigel > Sp60 organogel.

As explained previously, this may be attributed to the external

aqueous phase of hydrogels which facilitate DH release from

the formula in contrast to organogels which has an external

lipophilic phase that hinder the DH release. In addition the

aqueous external phase provides epidermal cell hydration and

swelling which enhances hydrophilic drug diffusion across SC.

PLO and bigels both contain external aqueous phase facilitating

the release of DH in addition to surface active components

which can enhance skin penetration ability.

4. Conclusion

The above mentioned results revealed that, the natures of the

active drug and other ingredients of the gels, as well as the vis-

cosity of the matrix, will affect the drug release profiles from

different gels. In vitro release and permeation studies indicated

prolonged release of DH from the tested organogels, hydrogels

and bigels. Hydrogel formulation gave better results among

other tested formulations. In vivo studies indicated that all

transdermal formulations can give sustained antihypertensive

effects.Organogelscaneffectively enhance thehydrophilic drug

deliveryacross the skinhowever this investigation revealed that

they could not be suggested as the vehicle of choice for trans-

dermal application of hydrophilic drugs. Conversely, watery gel

systems like hydrogels, PLO and bigelsmay be tried asmatrices

which hold good promise for transdermal drug delivery of DH.

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