Attenuation of low dose phenobarbital induction of hepatic microsomal aminopyrine N-demethylase activity in rats by cimetidine.
Cimetidine, a substituted imidazole, is an inhibitor of hepatic cytochrome P-450-mediated drug metabolism in rats and humans. We investigated the effect of cimetidine on phenobarbital induction of hepatic microsomal aminopyrine N-demethylase activity in the rat. Phenobarbital induction of aminopyrine N-demethylase was log-linear in the range of 1-6 mg/kg/day and the ED50 was approximately 3 mg/kg/day. Cimetidine 75 mg/kg (four times a day) attenuated the induction of aminopyrine N-demethylase activity by 58% in low dose (3 mg/kg/day) but not in high dose (40 mg/kg/day) phenobarbital treated rats. This result could not be explained by residual inhibition of enzyme activity by cimetidine and suggests that cimetidine affects the induction of hepatic cytochrome P-450 by low dose phenobarbital.
Faculty of Pharmaceutical Sciences, University of British Columbia, Vancouver, Canada.
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M
Levine
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Chang
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Bellward
D000633:Aminopyrine N-Demethylase / Q000378:metabolism*; D000818:Animals; D002927:Cimetidine / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004790:Enzyme Induction / Q000187:drug effects; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D010634:Phenobarbital / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains
D002927:Cimetidine; D000633:Aminopyrine N-Demethylase; D010634:Phenobarbital