The new angiotensin II receptor antagonist, irbesartan: pharmacokinetic and pharmacodynamic considerations

This article reviews the pharmacokinetics and pharmacodynamics of angiotensin II (AII) receptor antagonists (AIIRA), with particular focus on the novel compound irbesartan. Irbesartan has the highest oral bioavailability in its class (60% to 80%) and, unlike valsartan, its absorption is not affected by food. Irbesartan displays linear, dose related pharmacokinetics and, with the exception of tasosartan's active metabolite, has the longest elimination half-life of the AIIRA (11 to 15 h). Irbesartan exhibits the lowest amount of protein binding, limiting its potential for drug interactions. No drug interactions with irbesartan have been identified. Unlike losartan, candesartan, and tasosartan, irbesartan does not require biotransformation for AII blockade. The pharmacokinetics of irbesartan are not altered in renally or hepatically impaired patients, probably owing to excretion characteristic by both biliary and renal routes, or by differences in gender or age. Within its therapeutic dose range (150 to 300 mg), irbesartan shows sustained, dose related blockade 24 h after dosing. Irbesartan lowers blood pressure in a dose related manner up to 300 mg daily. Some clear differences in pharmacokinetics and pharmacodynamics exist among the AIIRA, which may have clinical implications.