Importance of metabolic stability and hepatic distribution to the pharmacokinetic profile of amlodipine

Abstract

1. In an isolated perfused rat liver (IPRL) model, the extensive hepatic uptake and subsequent slow redistribution of amlodipine into the perfusate have been demonstrated. The apparent liver volume for amlodipine was 920 ml compared with 38 ml for nitrendipine.

2. Metabolism is the major clearance mechanism of amlodipine and nitrendipine in animals and man. In the IPRL, the intrinsic (metabolic) clearance and first-pass extraction values for amlodipine are similar to those of nitrendipine. This is in contrast with in vitro metabolic stability data in rat liver microsomes which indicate about 40-fold greater metabolic stability for amlodipine.

3. The discrepancy between relative clearance rates for the two preparations may be explained by consideration of the hepatic volume of the two compounds, with the higher liver volume of amlodipine amplifying the whole organ clearance.