Topical Delivery of Diclofenac using Microemulsion Systems

The purpose of this study was to investigate microemulsions as delivery systems for diclofenac sodium (DS). Microemulsion systems were composed of: soybean oil, nonionic surfactants (Brij 58 and Span 80), and different alcohols: ethanol, and 1-buthanol as cosurfactant. The optimum surfactant: cosurfactant (S:CoS) weight ratios and microemulsion areas were detected by the aid of ternary phase diagrams. Five microemulsion with various values of: DS, 0.25-2.5% enhancer (menthol, farnesol), 4-20% oil, 20-70% bi-distilled water, 14-70% the mixture of surfactant and cosurfactant (w/w) were selected, and their physico-chemical properties like: pH, viscosity and conductivity were determined. Drug solubility in plain oil and microemulsions as well as partition coefficient respectively was estimated. The conductivity results showed that DS-loaded microemulsions have higher conductivity values (19.8-22.6 μS/cm) than unloaded formulations (15.5-17.2 μS/cm), and a load of DS into the formulation had no negative effect on system stability. Moreover, viscosity measurements were examined as a function of shear rate, and Newtonian fluid characterization was observed for each microemulsion system. All formulations had appropriate observed pH values varying from 6.50 to 7.15 for a topical application. The steady-state flux of DS from microemulsions and commercial gel were evaluated using Franz diffusion cells using synthetic membrane of carboximethylcellulose (CMC). The results suggest that microemulsions are potential vehicles for improved topical delivery of diclofenac. The release and the diffusion of DS from both microemulsions and commercial gels through a synthetic membrane established the advantages of microemulsions instead of commercial gels.