Pharmacokinetics of intramuscular piroxicam

The pharmacokinetics and bioavailability of two piroxicam formulations, 20-mg capsules for oral administration and 20-mg solution for intramuscular injection, were studied in 18 healthy male volunteers. A 40-mg dose was administered on the morning of the first two days, and a 20-mg dose on five subsequent days. Four weeks after the first dose was administered, the regimen was repeated, according to a crossover design. Plasma levels of piroxicam were measured with high performance liquid chromatography (HPLC) using ultraviolet detection at 340 nm. Results of ANOVA, Westlake, and Wilcoxon tests show that the two preparations are bioequivalent. The intramuscular solution, however, produces comparatively higher piroxicam plasma concentrations up to 45 minutes after the first 40-mg dose, up to 30 minutes after the second 40-mg injection, and up to 15 minutes after the 20-mg maintenance doses. The terminal half-lives were found to be 58.1 +/- 2.3 hours after intramuscular administration and 60.2 +/- 2.5 hours after oral dosing.