Four topical piroxicam gel products, including three locally made preparations (products B, C and D) and one innovator product (A), were evaluated in this study for their in vitro release through cellulose acetate membrane and for their in vitro permeation through new born pig skin. The in vitro data were then compared to the results from the in vivo pharmacological studies in animal models and the percutaneous absoption studies in humans using a novel skin stripping technique. All the in vitro release/permeation parameters (release rate, steady state flux and the cumulative amount released/permeated) of piroxicam did not significantly correlate with any of the in vivo parameters due to differences in the experimental conditions and permeation kinetics. However, it was found that were significant correlations between the ability of the gel products to reduce the size of blue spots, as induced by histamine, with the percent piroxicam absorption through the stratum corneum at 1 hr (r=0.9940, p<0.05) and at 3 hr (r=0.9502, p<0.05). In conclusion, the in vivo skin stripping method appeared to be a rapid and simple technique to evaluate the topical bioavailability of piroxicam gel products as well as their percutaneous absorption characteristics.
