title: Role of P-glycoprotein in pharmacokinetics and drug interactions of digoxin and beta-methyldigoxin in rats.
abstract: Digoxin and beta-methyldigoxin were evaluated pharmacokinetically in terms of P-glycoprotein (P-gp)-mediated drug interactions in rats. Evaluation was made by measuring the effects of a potent P-gp inhibitor (verapamil, cyclosporin A) on in vitro efflux transport of these compounds across the everted small intestine, on in situ absorption from the small intestine, and on in vivo total plasma clearance (CL(total)) as well as biliary and urinary excretions after intravenous administration. Both the intestinal efflux transport and absorption of beta-methyldigoxin were approximately 1.5-fold greater than those of digoxin, probably due to its higher lipophilicity. Addition of verapamil (300 microM) significantly decreased the intestinal efflux transport and increased the intestinal absorption of digoxin. In contrast, the influence of verapamil on beta-methyldigoxin was small. Intravenous cyclosporin A (30 mg/kg) significantly decreased in vivo CL(total) and biliary excretion of digoxin, but affected little on beta-methyldigoxin clearances. These results suggest that P-gp-mediated drug interactions can easily occur in digoxin, but hardly in beta-methyldigoxin. These findings may give a clue in selecting these digitalis compounds in clinical use, towards escape from P-gp-mediated drug interactions or reduction of interindividual variations.
authors.affiliation: Department of Pharmaceutics and Therapeutics, Programs for Pharmaceutical Sciences, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8551, Japan.
authors.forename: Sachiyo
authors.initials: S
authors.lastname: Funakoshi
authors.forename: Teruo
authors.initials: T
authors.lastname: Murakami
authors.forename: Ryoko
authors.initials: R
authors.lastname: Yumoto
authors.forename: Yoshie
authors.initials: Y
authors.lastname: Kiribayashi
authors.forename: Mikihisa
authors.initials: M
authors.lastname: Takano
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors / Q000502:physiology*; D000818:Animals; D016572:Cyclosporine / Q000494:pharmacology; D004077:Digoxin / Q000097:blood / Q000493:pharmacokinetics*; D004347:Drug Interactions / Q000502:physiology; D066298:In Vitro Techniques; D007408:Intestinal Absorption / Q000187:drug effects / Q000502:physiology; D008297:Male; D008520:Medigoxin / Q000097:blood / Q000493:pharmacokinetics*; D051381:Rats; D017208:Rats, Wistar; D014700:Verapamil / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D004077:Digoxin; D016572:Cyclosporine; D014700:Verapamil; D008520:Medigoxin