Preparation, characterization, and stability studies of piroxicam-loaded microemulsions in topical formulations.

The main purpose of this work was to determine the in vitro release of piroxicam in microemulsion formulations from different pharmaceutical topical preparations including different gel bases, such as, methyl cellulose (MC), carboxy methyl cellulose (CMC), hydroxypropyl methyl cellulose (HPMC), Carbopol 934, Carbopol 940, and Pluronic F-127 bases. The effect of the employed gel bases on the in vitro release profiles of piroxicam was examined to choose the base which gave the highest in vitro release. The kinetic treatments and parameters derived from in vitro release of piroxicam formulations were calculated according to different kinetic orders or systems. These gel formulations were selected for rheological and stability studies. Stability studies were conducted to investigate the change in drug content, viscosity, and pH of the semisolid formulations. The results showed that, the incorporation of piroxicam in microemulsion formulas could lead to enhancement of piroxicam release profiles by allowing constant and regular in vitro release. Three percent MC gel base showed the highest release of piroxicam-microemulsion after 180 min (97.70%) followed by 3% HPMC (94.0%) when compared to bases containing piroxicam alone. All the medicated gel bases containing piroxicam exhibit pseudoplastic flow with thixotropic behavior. The degradation of piroxicam from its topical formulations was found to be a zero-order reaction based on the mean value of correlation coefficients. All formulations were quite stable. The shelf life of the gel containing HPMC base was about 2.85 years. Considering the in vitro release, rheological properties and shelf life, HPMC gel base containing 0.5% piroxicam in a microemulsion formula was the best among the studied formulations.