title: Inducing properties of rifampicin and rifabutin for selected enzyme activities of the cytochrome P-450 and UDP-glucuronosyltransferase superfamilies in female rat liver.
abstract: Important species differences have been reported concerning the induction properties of rifampicin towards enzymes of the P-450 superfamily. Mice, rabbits and humans are far more responsive than rats and guinea pigs. In the present study a strong induction of cytochrome P-450 3A-dependent enzyme activities was observed in female rat liver microsomes after high dose treatment (> or = 250 mg/kg/day for 9 days) with rifampicin, resulting in an up to 30-fold enhanced hydroxylation rate of testosterone in the 2 beta-, 6 beta- and 15 beta-position in vitro. Other cytochrome P-450 isozyme-selective reactions were not, or only marginally, affected. A steep increase in cytochrome P-450 3A activity on a moderate elevation of the dose administered, together with the previously observed lack of efficient induction with doses below 200 mg/kg/day demonstrated that there is a threshold in enzyme induction by rifampicin. For rifabutin such a threshold was not apparent. Induction by rifabutin showed an isoenzyme-selectivity profile similar to that produced by rifampicin, but the maximally achievable induction of cytochrome P-450 3A by rifabutin was about two-fold lower compared with rifampicin. Rifampicin and rifabutin enhanced the glucuronidation of 1-naphthol, 4-hydroxybiphenyl and beta-estradiol by a factor of two to three. The potential implications of the enzyme induction by rifampicin derivatives in terms of possible drug-drug interactions are discussed.
authors.affiliation: Institute of Toxicology, University of Mainz, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Oesch
authors.forename: M
authors.initials: M
authors.lastname: Arand
authors.forename: M S
authors.initials: MS
authors.lastname: Benedetti
authors.forename: M G
authors.initials: MG
authors.lastname: Castelli
authors.forename: P
authors.initials: P
authors.lastname: Dostert
mesh_terms: D000818:Animals; D000904:Antibiotics, Antitubercular / Q000494:pharmacology; D003577:Cytochrome P-450 Enzyme System / Q000187:drug effects / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005260:Female; D014453:Glucuronosyltransferase / Q000187:drug effects / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D051381:Rats; D017208:Rats, Wistar; D017828:Rifabutin / Q000494:pharmacology* / Q000633:toxicity; D012293:Rifampin / Q000494:pharmacology* / Q000633:toxicity; D013739:Testosterone / Q000378:metabolism
chemical_list: D000904:Antibiotics, Antitubercular; D017828:Rifabutin; D013739:Testosterone; D003577:Cytochrome P-450 Enzyme System; D014453:Glucuronosyltransferase; D012293:Rifampin