Formulation and Evaluation of Griseofulvin Solid Dispersion incorporated gel for topical application

Sonam Shukla*, Swarnakshi Upadhyay, Rajneesh Kumar Gupta

Kanpur Institute of Technology, Kanpur, Uttar Pradesh, India.

*Corresponding Author E-mail: sonamkitpmph21@gmail.com

ABSTRACT:

In the present investigation, griseofulvin loaded solid dispersion were formulated using mannitol and PVP K30 as the hydrophilic carriers. The best formulation was then loaded in to gel formulation prepared either from carbopol 934P or HPMC. Melting method was adopted to prepare the solid dispersions of griseofulvin. The drug content was found to be highest in the formulation SD6 (94.60±0.7%) and the lowest in formulation SD1 (91.56 ±0.251%). A minimum of 10 fold increase in solubility was witnessed after formulating griseofulvin as SD. The minimum solubility was exhibited by SD1 (0.57±0.04mg/mL) whereas SD6 exhibited the highest solubility (2.09±0.080 mg/mL). SD6 released 47.16±1.167% after 15 min and around 80% drug released at 30 min. Hence SD6 was used for further formulation as gel. The pH value of all gel formulations lies within the 5.29 to 6.81 and they were homogeneous and uniform. The viscosity of the formulations ranged from 491±31 cp to 668±57.5 cp. The maximum amount of drug was released from formulation SDG2 (72.37%) followed by SDG4 (64.91%) by the end of 6^th hour of the study. The formulation containing 1.0% of carbopol 934 was the gelling agent was considered to be the best formulation of all the prepared gels.

KEYWORDS: Solid dispersion, Griseofulvin, Gel, Melting method, Franz diffusion cell, Solubility.

INTRODUCTION:

The feasibility of administering a drug via a topical or transdermal route may incur several difficulties that may result in unwanted side effects.¹ Colloidal drug delivery systems have arisen as popular approaches that can overcome these obstacles, thereby enhancing the drug accumulation, absorption, and delivery to targeted sites. An effective colloidal formulation that can be applied in skin delivery is a solid dispersion (SD), in which the drug is dispersed in inert carriers. An SD has the ability to reduce the dispersed particle size, convert the drug from the crystalline to the amorphous state, and augment its wetting capability, which greatly contribute to the solubility improvement of poorly water-soluble drugs.¹

Griseofulvin is a widely acknowledged antifungal drug used used orally to treat superficial fungal infections, primarily fingernail and toenail infections, but it does not penetrate skin or nails if used topically.²

The lower aqueous solubility and absorption causes the dose of griseofulvin to be very high (500mg/kg, twice a day in adults). On the other hand only 25-50% of the drug is absorbed and with around 42% drug excreted unchanged in urine after 4 hours thereby decreasing its half-life.

SD is now firmly established as a platform technology for the formulation of poorly soluble drugs.^3-10 Specifically, SD technology has been successfully applied to develop formulations with a high drug and/or containing drugs with a high tendency to crystallize.

As the absorption of drug is low, formulating it as solid dispersion would be helpful to improve its solubility and in turn its absorption and bioavailability.

Incorporating solid dispersions into water-based gels offers wide advantages as the absorption of drug occurs better through the skin when applied as gels and solid dispersions allow proper incorporation of hydrophobic drugs into the gel matrix.¹¹

The present investigation was conducted with an objective to improve the topical-systemic delivery of griseofulvin by formulating solid dispersion containing the drug griseofulvin for improving the aqueous solubility and incorporating the solid dispersion in to water-based gel for optimal and compliant topical application.

MATERIAL AND METHODS:

Griseofulvin pure drug was purchased from Yarrow Pharmaceuticals, Mumbai; PVP K30 was procured from HiMedia, Mumabi; Mannitol was purchased from Fischer Scientific, Mumbai; Carbopol 934P, HPMC and all other reagents and chemical were obtained from Oxford Fine Chemicals, Mumbai.

The preformulation studies were conducted for physical characterization, solubility, melting point and compatibility between the drug and the excipient used. The calibration curve of griseofulvin was constructed by UV spectrophotometry at 295nm using methanol as the solvent.¹²

Formulation of Solid Dispersion of Griseofulvin:

The SD of griseofulvin was designed using I-optimal factorial approach, measuring the effect of formulation variables on the measured responses. The independent variables for formulation were the drug to polymer (D:P) ratio (X1) and the polymer type (X2). The chosen response for measurement was the percentage dissolution efficiency at 15min.

The melting method was used for the preparation of solid dispersion. The drug and polymer were mixed physically in a porcelain dish and heated on a paraffin bath till molten. The molten mixture was poured on a clean tile and allowed to cool and solidify.¹³ The resulting solidified mass was dried, finely ground in a mortal pestle and passed through sieve # 100.

Evaluation of griseofulvin SD:

Drug content of solid dispersion:

An accurately weighed 10mg of the SD was taken in a 25mL volumetric flask and dissolved in methanol by sonication for 15 min. The volume was made up to the mark with methanol. A portion of the above solution was withdrawn and centrifuged for 10 min. 5mL of the supernatant was suitably diluted and analyzed spectrophotometrically at 295nm.

Solubility study:

An excess amount of the SD was transferred to stoppered Erlenmeyer flask and 25mL of phosphate buffer pH 7.4 was added to it. The mixture was sonicated for 1h and 2mL of the solution was withdrawn, filtered through Whatman filter paper no. 40 and analyzed spectrophotometerically at 295nm after appropriate dilution.

Dissolution study:

Accurately weighed formulation from each batch, equivalent to 25mg of griseofulvin was added to 900ml of dissolution media (phosphate buffer, pH 7.4) contained in USP dissolution apparatus II (Paddle type) and stirred at a speed of 50rpm at 37±0.5°C. 5mL of sample were withdrawn at 5, 10, 15, 20 and 30 min and the medium was enriched with 5 ml of fresh dissolution media (37°C). The collected samples were analyzed after suitable dilution at 295nm using UV-visible spectrophotometer against the phosphate buffer, pH 7.4 as blank. The dissolution of pure griseofulvin was studied similarly. The dissolution efficiency of SD at 15 min was determined from the release data.

Formulation of SD loaded gel^14-16:

Gel loaded with SD of griseofulvin were formulated using two gel forming polymers (Carbopol 934P and HPMC) using different concentration of the polymers and fixed amount of SD.

Gel formulation using carbopol:

The accurately weighed quantity of the solid dispersion (table 2) was dispered in purified water with constant stirring and the drug solution was heated to 50°C. The amount of carbopol was added to the solution under continuous stirring while maintaining the temperature at 50°C to ensure no air entrapment. The dispersion of the gelling agent was neutralized using triethanolamine solution to neutral pH and the stirring was continued to obtain a clear gel.

Gel formulation using HPMC:

The accurately weighed quantity of the solid dispersion (table 2) was dispered in purified water with constant stirring and the drug solution was heated to 50°C. The amount of HPMC was added to the solution under continuous stirring while maintaining the temperature at 50°C to ensure no air entrapment. The dispersion of the gelling agent was neutralized using 10% NaOH solution to neutral pH and the stirring was continued to obtain a gel.

Table 2 Batch formula for griseofulvin SD loaded gel

Ingredient	Batch formula for 100g gel
Ingredient	SDG1	SDG2	SDG3	SDG4	SDG5	SDG6
SD (g)	1.0	1.0	1.0	1.0	1.0	1.0
Carbopol 934	0.5	1.0	1.5	-	-	-
HPMC	-	-	-	0.5	1.0	1.5
Triethanolamine (mL)	QS	QS	QS	-	-	-
10% NaOH (mL)	-	-	-	QS	QS	QS
Water (mL)	98.5	98.0	97.5	98.5	98.0	97.5

QS – Quantity sufficient (to cause neutralization of pH)

Evaluation of gel:

Homogeneity:

All the gel formulations were evaluated for homogeneity by visual inspection after the gels were well set in the container. They were observed for their appearance and presence of any aggregates.

Grittiness:

All the formulations were evaluated under a light microscope for the presence of particlulate matter. The absence of particles fulfills the criterion for a good gel formulation.

pH determination:

1gram of gel was dissolved in 100ml of distilled water and allowed to stand for 2 h. The pH of the resulting solution of each formulation was measured using digital pH meter in triplicate and average values were calculated.

Viscosity:

The measurement of viscosity of the prepared gel was done with a Brookfield Viscometer. The gels were rotated at 20rpm using spindle no. 64 and the corresponding dial reading was recorded as the viscosity values. The viscosity was measured in centipoises (cp).

Rheological Study:

The gel formulations were subjected to shear stress (rpm) by rotating the spindle no. 64 at 10, 20, 40, 60, 80, and 100rpm for 15 min and viscosity in centipoise was determined.

Spreadability:

The spreadability of the gels was determined using Arvouet-Grand Method.¹⁷ Briefly, 1g of the gel was pressed between two 20 X 20cm horizontal plates. A weight of 125g is placed on the upper plate for 1 min and diameter of spreading of gel was recorded. The spreadability of formulations was measured in triplicate and the average value was determined.

Drug content:

100mg of gel was dissolved in 100mL phosphate buffer pH 7.4 and shaken using a mechanical shaker for 2 h to dissolve the contents completely. The solution was then filtered and the drug content was determined spectrophotometrically at 295nm using a blank solution (phosphate buffer pH 7.4).

In-vitro Drug Diffusion Study:

In-vitro drug diffusion study of all gel formulations were performed by using Franz-diffusion cell. The egg membrane was used in drug diffusion study and mounted in between the receptor and donor compartment of the Franz-diffusion cell. The receptor compartment contained 10mL of phosphate buffer pH 7.4 and maintained the temperature at 37±1°C. The assembly was kept in a fix position on a magnetic stirrer. 0.1g quantity of gel sample was placed over the egg membrane and solution of phosphate buffer pH 7.4 in the receptor compartment was stirred continuously using magnetic bead at 50rpm. Samples of 1mL were withdrawn at 1, 2, 3, 4, 5 and 6 h and diluted with 10ml of blank solution (phosphate buffer, pH 7.4) and analyzed using spectrophotometer at 295nm.

RESULT AND DISCUSSION:

The sensory organ (eye, tongue, skin and nose) have been used to perform the organoleptic evaluation of griseofulvin. The melting point has been determined using open capillary method and the result of the same is reported uncorrected for environmental factors (table 3).

Table 3 Organoleptic features and melting point of griseofulvin

S. No.	Characteristic	Specification [57]	Observed
1	Color and appearance	White to pale-cream; crystalline	Pale-cream; amorphous
2	Taste	Tasteless	Slightly bitter
3	Odor	Odorless	Odorless
4	Melting Point	220°C	224-226°C
5	Solubility	Soluble in DMF; slightly soluble in ethanol, methanol, chloroform, acetone, acetic acid, benzene and ethyl acetate; practically insoluble in water	Soluble in methanol, chloroform; slightly soluble in water and ethanol

Figure 1 FTIR spectrum of (a) griseofulvin; (b) PVP K30 + griseofulvin; (c) Mannitol + griseofulvin

Figure 2 (a) UV spectrum of griseofulvin; (b) Calibration curve of griseofulvin

6.2 Compatibility study by FTIR:

The FTIR spectrum of griseofulvin (figure 1a) exhibited significant peaks of C-N stretch, C=O stretch, C-O-C stretch, N-H and O-H stretch and the peaks were compared to the standard spectra available at NIST.¹⁸No deletion of the characteristic peaks of griseofulvin was found in the FTIR spectrum of the physical mixtures of drug and polymer (figure 1b, 1c).

The calibration curve of griseofulvin was constructed in methanol at concentration range of 10-60 µg/mL. The λmax was found to be 295 nm and was used for all the analysis of drug.

The I-optimal design model was used for formulation of batches as it has been previously reported that the drug-polymer ratio and the type of polymer play a vital role the solubility enhancement by the SD.¹⁹ Three different ratio of drug to polymer were tested and two polymeric material were used to obtain the most effective combination for enhancing the dissolution of the drug form SD in 15 min. Melting method was utilized for preparation of SD; the basis of melting method is direct heating of a physical mixture of the drug and a hydrophilic carrier resulting into melting at temperature slightly exceeding the eutectic point of the mixture.

The drug content was found to be highest in the formulation SD6 (94.60±0.7%) and the lowest in formulation SD1 (91.56±0.251%). A minimum of 10 fold increase in solubility was witnessed after formulating griseofulvin as SD. The minimum solubility was exhibited by SD1 (0.57±0.04mg/mL) whereas SD6 exhibited the highest solubility (2.09±0.080mg/mL).

Table 3 Drug content and solubility of griseofulvin in SD

Formulation	Drug content (%)	Solubility (mg/mL)
SD1	91.56 ± 0.251	0.57 ± 0.04
SD2	92.20 ± 0.321	0.81 ± 0.060
SD3	94.23 ± 0.351	1.28 ± 0.078
SD4	92.46 ± 0.404	0.92 ± 0.045
SD5	93.43 ± 0.251	1.20 ± 0.040
SD6	94.60 ± 0.7	2.09 ± 0.080
Griseofulvin	-	0.062 ± 0.005

Table 4 Cumulative release of griseofulvin from SD

Time (min)	Cumulative drug release (%)
Time (min)	SD1	SD2	SD3	SD4	SD5	SD6
0	0	0	0	0	0	0
5	2.3 ± 0.916	5.06 ± 0.321	8.5 ± 0.529	6.16 ± 0.321	8.06 ± 0.757	12.33 ± 1.628
10	5.06 ± 0.251	14.4 ± 1.493	20.53 ± 1.721	14.13 ± 0.702	18.66 ± 1.209	29.46 ± 2.350
15	8.2 ± 1.014	19.16 ± 1.205	26.26 ± 0.378	20.99 ± 1.607	36.73 ± 1.234	47.16 ± 1.167
20	11.93 ± 1.115	26.23 ± 1.955	31.3 ± 0.754	34.16 ± 1.450	52.56 ± 2.103	61.83 ± 1.026
30	16.43 ± 0.709	34.73 ± 1.274	40.8 ± 0.984	48.23 ± 1.677	65.7 ± 1.734	79.86 ± 0.305

Table 5 pH, viscosity, homogeneity and spreadability of SD6 loaded gel

Formulation No.	pH	Viscosity (cp)	Spreadability (mm)	Drug Content (%)	Homogeneity
SDG1	6.02 ± 0.011	491 ± 31	58.6 ± 2.15	94.82 ± 0.32	Homogenous and non gritty
SDG2	6.44 ± 0.020	537 ± 41.5	46.0 ± 0.80	96.10 ± 0.92	Homogenous and non gritty
SDG3	6.81 ± 0.005	624 ± 36.8	25.3 ± 0.80	94.41 ± 0.77	Homogenous and non gritty
SDG4	5.29 ± 0.015	518 ± 27.1	53.1 ± 1.41	95.36 ± 0.61	Homogenous and non gritty
SDG5	5.87 ± 0.001	601 ± 46.9	39.7 ± 1.64	96.64 ± 1.01	Homogenous and non gritty
SDG6	6.62 ± 0.004	668 ± 57.5	23.4 ± 1.41	95.11 ± 0.69	Homogenous and non gritty

The dissolution (drug release) of griseofulvin from the SD was studied using USP type II dissolution apparatus and the percent cumulative drug release at 15 min was considered as the criterion for selection of the best SD formulation (table 4).

As drug dissolution at 15 min was selected as the criteria for optimization of the independent variables (D:P ratio and polymer type), it was found that SD6 containing 1:3 ratio of griseofulvin to mannitol was the best formulation of all with 47.16±1.167% drug release after 15min and around 80% drug released at 30min. Hence SD6 was used for further formulation as gel.

6.5 Evaluation of SD6 loaded gel:

The results of pH, viscosity, homogeneity and spreadability are shown in table 5. For all formulations, the pH value lies within the 5.29 to 6.81 which is within range compatible with the pH of the skin (4.5 to 7.4). The results also indicate that the low viscosity of the gels can be helpful for the application of delivery to skin.

The homogeneity of all gels was evaluated by the visual inspection after the gels was placed in the containers. No particle was appeared under the light microscope. This evaluation conformed that the gels were uniformly prepared.

The viscosity of the formulations ranged from 491±31 to 668±57.5 depending on the concentration of the gelling agent. The spreadability was determined using the Arvouet-Grand Method wherein the spread diameter under the experimental conditions is used as a measure of the stiffness or fluidity of the gel. The gel is considered to be semi stiff if the spread diameter is less than or equal to 50mm and fluid if the diameter is more than 50mm but less than 70mm.²⁰ From the results it was found that the formulations containing 1.0 and 1.5 % of gelling agent were semi stiff in nature and the formulations with 0.5% gelling agent was very fluidic and non very suitable for topical application.

The rheological behavior of the formulations exhibited pseudoplastic flow as indicated by shear thinning (figure 3). This indicates that the gel formulations could be easily extrudable from the tubes containing them or would have excellent syringe ability.

Figure 3 Effect of shear on viscosity of gel

Figure 4 Comparative in vitro diffusion profile of griseofulvin from SD loaded gels

The in vitro diffusion of griseofulvin from the SD loaded gel formulations was studied using Franz diffusion cell. Freshly peeled egg membrane was used to simulate the skin characteristics for diffusion study. The maximum amount of drug was released from formulation SDG2 (72.37%) followed by SDG4 (64.91%) by the end of 6^th hour of the study (figure 4). The formulation containing 1.0% of carbopol 934 was the gelling agent was considered to be the best formulation of all the prepared gels.

CONCLUSION:

The objective of the investigation was to improve the solubility of griseofulvin by formulating as solid dispersion and loading the solid dispersion into gel for topical application of the formulation. From the present investigation it could be concluded that the gel formulation SDG2 (prepard using 1% carbopol as the gelling agent and triethanolamine as the crosslinking agent) loaded with SD6 (prepared using 1:3 ratio of griseofulvin: mannitol) might be the best formulation exhibiting good in vitro diffusion profile, viscosity and spreadability.

ACKNOWLEDGEMENT:

The authors would like to thank the management of Kanpur Institute of Technology & Pharmacy for providing the necessary facilities for conducting the research work.

CONFLICT OF INTEREST:

The authors report no conflict of interests.

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Received on 05.07.2021 Modified on 07.12.2021

Research J. Pharm. and Tech 2022; 15(10):4389-4394.

DOI: 10.52711/0974-360X.2022.00736