Pharmacokinetic analysis of enterohepatic circulation of piroxicam in rabbits

The concentration (c)-time (t) curves of piroxicam showed double peaks following iv 10 mg dose to 4 rabbits. A new mathematical model of enterohepatic circulation was proposed to explain this double-peak phenomenon and showed good agreement with data. This model provides not only the common pharmacokinetic parameters: T1/2 = 1.12 +/- 0.32 h, V1 = 0.64 +/- 0.12 L, AUC = 34.7 +/- 7.8 micrograms.h-1.ml-1, but also the parameters of enterohepatic circulation of piroxicam: the cycling amount of drug Db = 3.9 +/- 1.4 mg, reabsorption fraction Fb = 0.50 +/- 0.04, reabsorption rate constant Ka = 2.55 +/- 0.50 h-1. It is indicated in this study that enterohepatic circulation results in a 20% average increase of the effective amount of piroxicam.