Physicochemical Characterization and Clinical Evaluation of a Microemulsion System for Topical Delivery of Tazarotene in Psoriasis

The purpose of the present study was to evaluate the potential application of microemulsion as a dermal drug delivery system for a poorly water soluble drug-tazarotene and enhance its topical bioavailability. Various oils were screened based on solubility studies and isopropyl myristate was selected as the oil phase. Pseudo-ternary phase diagrams were developed for various microemulsion formulations composed of isopropyl myristate (oil phase), Tween 80 (surfactant), propylene glycol (cosurfactant) and water. The physicochemical properties and the permeability of tazarotene were investigated for the optimized microemulsion. This developed microemulsion was incorporated into Carbopol 934 based gel to facilitate its topical application. In-vitro drug diffusion of optimized formulation was studied using Franz diffusion cells. In-vitro drug diffusion after 8 h from the microemulsion incorporated gel was 72.01± 2.50%, while that from Tazret® (marketed product) was 61.59± 2.03%. Ex-vivo study using rat skin indicated that microemulsion incorporated gel had better skin deposition capacity (18.23± 1.00%) as compared to marketed formulation (7.23± 0.66%). The clinical efficacy of the test formulation was evaluated in psoriasis patients. Percent change in Psoriasis status after 6 weeks was 4.80± 1.74% and 17.36± 0.98% in treatment with ME incorporated gel and Tazret® respectively (p value < 0.05). The higher efficacy of the developed microemulsion system was attributed to the combined effect of increased solubility and reduced droplet size of microemulsion systems leading to increased deposition in the skin. The results suggest that microemulsions are potential vehicles for improved topical delivery of tazarotene to treat psoriasis. Keywords: Microemulsion, pseudo-ternary phase diagram, tazarotene, topical bioavailability, topical drug delivery.