The use of 1-aminobenzotriazole in differentiating the role of CYP-mediated first pass metabolism and absorption in limiting drug oral bioavailability: a case study.

Preliminary studies in our laboratory demonstrated low oral bioavailability of Drug X in male Sprague Dawley rats. However, the factors responsible for the observed poor bioavailability were not well understood. The objective of this study was to investigate the contribution of cytochrome P450(s) metabolism to the observed poor oral bioavailability of Drug X in male Sprague-Dawley rats in the presence of 1-aminobenzotriazole, a non-specific irreversible inhibitor of cytochrome P450s. Male Sprague-Dawley rats were pre-treated with or without oral 1-aminobenzotriazole (50 mg/kg) two hours prior to receiving a single intravenous or oral dose of Drug X (3 mg/kg). Blood samples were collected from animals at different time points over six hours following Drug X dosing. Plasma concentrations of Drug X were determined using LC/MS/MS. Pharmacokinetic data obtained from an intravenous dose study in rats suggested that Drug X exhibited a high clearance (55 mL/min/kg) and moderate volume of distribution (1.3 L/kg) with short half-life in rats (0.7 hr). Oral dosing of Drug X to rats resulted in low oral bioavailability (19%). 1-aminobenzotriazole pre-treatment of male Sprague Dawley rats followed by an intravenous dose of Drug X resulted in a decrease in plasma clearance by 71% and an increase in half-life by 100%, without affecting the volume of distribution. Furthermore, the oral bioavailability of Drug X increased markedly with 1-aminobenzotriazole pre-treatment. However, the fraction absorbed of Drug X did not significantly change with 1-aminobenzotriazole pre-treatment. The results of this study indicated that CYP-mediated metabolism played a major role in limiting the oral bioavailability of Drug X in rats. The data suggests that 1-aminobenzotriazole can be used as an effective tool in assessing the factors contributing to the poor oral bioavailability of drugs.