title: Drug metabolism by rat and human hepatic microsomes in response to interaction with H2-receptor antagonists.
abstract: Cimetidine has been reported to decrease plasma clearance of drugs in humans and animals. This reduction in hepatic drug metabolism could be due to cimetidine's intrinsic H2-receptor blocking activity. Alternatively, the imidazole ring structure of cimetidine could explain these observations because imidazole derivatives have been reported to be potent inhibitors of hepatic microsomal drug metabolism. Rat and human hepatic microsomal drug metabolism in the presence of cimetidine and ranitidine, a nonimidazole H2-receptor antagonist, have been studied. High binding affinity of cimetidine for cytochrome P 450(Ks = 31 micro M) was seen, while no evidence for ranitidine binding to cytochrome P450- was observed. Cimetidine inhibited meperidine and pentobarbital metabolism by both rat and human hepatic microsomes while ranitidine did not affect these two cytochrome P450-medicated biotransformation reactions. Conjugation of morphine, a reaction not mediated by cytochrome P450, was unaffected by either cimetidine or ranitidine. The imidazole structure of cimetidine rather than its H2-receptor blocking activity is primarily responsible for cimetidine-induced inhibition of hepatic drug metabolism.
mesh_terms: D000818:Animals; D002927:Cimetidine / Q000494:pharmacology*; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D005663:Furans / Q000494:pharmacology*; D006146:Guanidines / Q000494:pharmacology*; D006635:Histamine H2 Antagonists / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008614:Meperidine / Q000378:metabolism; D008862:Microsomes, Liver / Q000187:drug effects* / Q000378:metabolism; D009020:Morphine / Q000378:metabolism; D011899:Ranitidine; D051381:Rats; D011919:Rats, Inbred Strains; D011970:Receptors, Histamine H2 / Q000187:drug effects; D013329:Structure-Activity Relationship
chemical_list: D005663:Furans; D006146:Guanidines; D006635:Histamine H2 Antagonists; D011970:Receptors, Histamine H2; D009020:Morphine; D002927:Cimetidine; D011899:Ranitidine; D003577:Cytochrome P-450 Enzyme System; D008614:Meperidine