Effects of enzyme inducers and inhibitors on the pharmacokinetics of intravenous omeprazole in rats

A series of experiments using various inducers and inhibitors of the hepatic microsomal cytochrome P450 (CYP) isozymes were conducted to find CYP isozymes responsible for the metabolism of omeprazole in male Sprague-Dawley rats. Omeprazole, 20mg/kg, was administered intravenously. In rats pretreated with SKF 525-A (a nonspecific CYP isozyme inhibitor in rats), the time-averaged nonrenal clearance (Cl-nr) Was significantly slower (77.1% decrease) than that in untreated rats. This indicated that omeprazole is metabolized via CYP isozymes in rats. Hence, rats were pretreated with various enzyme inducers and inhibitors. In rats pretreated with 3-methyl-cholanthrene and dexamethasone (main inducers of CYP1A1/2 and 3A1/2 in rats, respectively), the Clnr values were significantly faster (43.8% and 26.3% increase, respectively). In rats pretreated with troleandomycin and quinine (main inhibitors of CYP3A1/2 and 2D1 in rats, respectively), the Cl-nr values were significantly slower (20.9% and 12.9% decrease, respectively). However, the Cl-nr values were not significantly different in rats pretreated with orphenadrine, isoniazid and sulfaphenazole (main inducers of CYP2B1/2 and 2E1, and a main inhibitor of 2C11, respectively, in rats) compared with those of respective control rats. The above data suggested that omeprazole could be mainly metabolized via CYP1A1/2, 3A1/2 and 2D1 in male rats. Copyright (c) 2006 John Wiley & Sons, Ltd.