Albendazole repeated administration induces cytochromes P4501A and accelerates albendazole deactivation in mouflon (Ovis musimon).

Adult mouflon ewes (Ovis musimon) were treated repeatedly with therapeutic doses of albendazole (ABZ, p.o. 7.5 mg/kg of body weight/day, for five consecutive days). Animals (treated or control) were sacrificed 24 h after the fifth dose of ABZ and liver and small intestine were collected to prepare microsomes. The activities of several biotransformation enzymes were measured in both hepatic and intestinal microsomes. A significant increase in the activity and amount of cytochromes P4501A (CYP1A) was observed in both tissues of ABZ treated mouflons compared to control animals. No other biotransformation enzymes tested were affected by five ABZ doses. The in vitro biotransformation of ABZ was studied in hepatic and intestinal microsomes from ABZ treated and control mouflons. Concentrations of two main ABZ metabolites - pharmacologically active ABZ sulfoxide and pharmacologically inactive ABZ sulfone were analysed using HPLC. A significant increase in rate of formation of ABZ sulfone (which is catalysed by CYP1A) was observed in hepatic as well as in intestinal microsomes from ABZ treated animals. The enhancement of ABZ deactivation by its repeated administration may affect the anthelmintic efficacy of this drug and may contribute to the development of parasite resistance.