title: Comparison of the effects of the new azalide antibiotic, azithromycin, and erythromycin estolate on rat liver cytochrome P-450.
abstract: Erythromycin and some other macrolide antibiotics can first induce a cytochrome P-450 isozyme similar to the one induced in rats by pregnenolone-16 alpha-carbonitrile and then inhibit it by forming a stable cytochrome P-450-metabolite complex. The purpose of this study was to compare azithromycin, a novel 15-membered ring azalide, and erythromycin estolate for the potential to cause hepatic microsomal enzyme induction and inhibition in Sprague-Dawley rats. The daily oral administration of 800 mg of erythromycin estolate per kg for 7 days resulted in statistically significant elevations of NADPH-cytochrome c reductase, erythromycin N-demethylase (3.2-fold), and total cytochrome P-450 content. Approximately 40% of cytochrome P-450 was complexed with erythromycin metabolite. In contrast, the daily administration of 200 mg of azithromycin per kg for 7 days caused significant elevations of N-demethylase (2.5-fold) only and did not produce any increases in total cytochrome P-450 content or NADPH-cytochrome c reductase. No complexed cytochrome P-450 was detected in the azithromycin-dosed rats despite liver concentrations of azithromycin that were 118 times greater than the liver concentrations of erythromycin estolate in erythromycin estolate-dosed rats. Although the short-term oral administration of azithromycin produced hepatic accumulation of the drug and elevated azithromycin demethylase activity, there was no other evidence of hepatic cytochrome P-450 induction or inactivation via cytochrome-metabolite complex formation. In contrast to erythromycin estolate, azithromycin is not expected to inhibit its own metabolism or that of other drugs via this pathway.
authors.affiliation: Drug Safety Evaluation Department, Pfizer Central Research, Groton, Connecticut 06340.
authors.forename: D E
authors.initials: DE
authors.lastname: Amacher
authors.forename: S J
authors.initials: SJ
authors.lastname: Schomaker
authors.forename: J A
authors.initials: JA
authors.lastname: Retsema
mesh_terms: D000818:Animals; D017963:Azithromycin; D001835:Body Weight / Q000187:drug effects; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000187:drug effects; D004917:Erythromycin / Q000031:analogs & derivatives* / Q000494:pharmacology; D004918:Erythromycin Estolate / Q000494:pharmacology*; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D008837:Micrococcus / Q000187:drug effects; D008861:Microsomes / Q000378:metabolism; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D006899:Mixed Function Oxygenases / Q000378:metabolism; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D011285:Pregnenolone Carbonitrile / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D065607:Cytochrome P-450 Enzyme Inhibitors; D011285:Pregnenolone Carbonitrile; D004917:Erythromycin; D017963:Azithromycin; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D009251:NADPH-Ferrihemoprotein Reductase; D004918:Erythromycin Estolate