A Comparison of Oil-In-Water and Water-In-Oil Microemulsions for Enhancing Piroxicam Permeation Through Skin

Microemulsions consisting of vitamin E acetate (oil phase), Labrasol (R) and Plurol Oleique (R) (surfactant phase) were developed for transdermal delivery of a water insoluble non-steroidal anti-inflammatory drug (NSAID) piroxicam. Oil-in-water (o/w) and water-in-oil (w/o) microemulsions were formulated and their physicochemical properties were determined prior to in vitro skin permeation studies using Wistar rat skin in a modified Franz diffusion cell. The optimal o/w and w/o microemulsion contained vitamin E acetate (14% and 19%), 3: 1 of Labrasol (R) : Plurol Oleique (R) (56% and 73%), and water (30% and 8%), respectively. To compare, o/w microemulsions exhibited similar piroxicam loading to w/o microemulsions (0.4 mg/g) but smaller droplet size (66 nm vs 157 nm) and higher drug incorporation efficiency (86% vs 75%). Drug permeation in rat skin following topical application of o/w microemulsions was found to be significantly greater (763 mu g/cm(2)) than that obtained using w/o microemulsion (411 mu g/cm(2)) and piroxicam solution in water (459 mu g/cm(2)) (p < 0.05). The release profile of piroxicam from microemulsions fitted the zero order model while the profile for piroxicam solution followed first-order kinetics. Both types of piroxicam microemulsion were stable on storage at room temperature for at least three months. These findings demonstrate that o/w microemulsions offer significant potential as transdermal delivery systems for piroxicam in the treatment of acute and chronic rheumatoid arthritis.