Inhibition of hepatic microsomal drug metabolism in rats by five calcium antagonists.
The effects of five calcium antagonists, verapamil, diltiazem, nifedipine, darodipine and isradipine, on rat liver microsomal drug metabolism in vitro and in vivo were studied. All compounds prolonged hexobarbital-induced sleeping time in a dose-dependent manner (doses 3.0 and 30.0 mg/kg, except nifedipine 0.3 and 3.0 mg/kg) and inhibited cytochrome P450-dependent N-demethylation of aminopyrine in vitro in rat liver microsomes. The incubation of all compounds with microsomes resulted in the apparent formation of formaldehyde, suggesting either N- or O-demethylation. Diltiazem, isradipine and darodipine gave rise to a type I spectral change. Nifedipine seemed to produce a type II spectral change. A spectrum of verapamil changed from a type I to a type II as concentration increased. These results indicate that all calcium antagonists studied interact with P450 and are in vitro inhibitors of microsomal drug metabolism in the rat and the inhibition brings out pharmacokinetic drug-drug interactions in vivo.
Department of Pharmacology and Toxicology, University of Oulu, Finland.
J
J
Mäenpää
H
H
Ruskoaho
O
O
Pelkonen
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D003864:Depression, Chemical; D005260:Female; D006591:Hexobarbital / Q000494:pharmacology; D066298:In Vitro Techniques; D008862:Microsomes, Liver / Q000201:enzymology / Q000378:metabolism*; D006899:Mixed Function Oxygenases / Q000378:metabolism; D004364:Pharmaceutical Preparations / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012890:Sleep / Q000187:drug effects
D002121:Calcium Channel Blockers; D004364:Pharmaceutical Preparations; D006591:Hexobarbital; D006899:Mixed Function Oxygenases