title: Metabolic interaction between cyclosporine and sirolimus.
abstract: BACKGROUND
  When the immunosuppressants cyclosporine (CsA) and sirolimus (SRL) are co-administered to transplant patients, lower doses are used than when either drug is given alone. Since both drugs share similar transport and metabolic pathways, there is the potential for an interaction leading to unpredictable effects. Furthermore, both drugs affect the activity of cytochrome P450 3A1/2 (CYP3A1/2), the rat parallel to human CYP3A4, and the multidrug transporter P-glycoprotein (Pgp).
  
  
  METHODS
  To clarify the role of metabolic enzymes and membrane transporters involved in the disposition of both drugs, we examined hepatic CYP3A1/2, Pgp, and multidrug resistance gene (mdr) mRNA during chronic therapy with CsA and SRL in salt-depleted rats. Specifically, rats were given intravenous doses of CsA 2.5 mg/kg and SRL 1 mg/kg, alone or in combination, for two weeks via constant rate intravenous infusion.
  
  
  RESULTS
  CsA treatment inhibited hepatic CYP3A1/2 protein expression, catalytic activity, and mRNA levels. SRL dosing suppressed CYP3A1/2 protein expression and catalytic activity, without affecting mRNA. With combined dosing, however, there was a much greater reduction. Hepatic Pgp protein levels were elevated after treatment with either drug alone, as well as with combined dosing. Compared to controls, there were significant increases in mdr1a and mdr1b mRNA levels in all treatment groups, with the combined drugs causing the greatest increase.
  
  
  CONCLUSIONS
  Both CYP3A1/2 and Pgp participate in the disposition of CsA and SRL in rats. Changes in the individual activities of CYP3A1/2 and Pgp may contribute to an interaction between CsA and SRL resulting in unanticipated effects during chronic therapy.
authors.affiliation: Pharmaceutics Division, College of Pharmacy, The University of Texas at Austin, Austin, TX 78712-0126, USA.
authors.forename: Shuang
authors.initials: S
authors.lastname: Bai
authors.forename: Stanislaw M
authors.initials: SM
authors.lastname: Stepkowski
authors.forename: Barry D
authors.initials: BD
authors.lastname: Kahan
authors.forename: Lane J
authors.initials: LJ
authors.lastname: Brunner
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism*; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism*; D016572:Cyclosporine / Q000494:pharmacology*; D051544:Cytochrome P-450 CYP3A; D004347:Drug Interactions; D019450:Genes, MDR / Q000187:drug effects; D007166:Immunosuppressive Agents / Q000378:metabolism* / Q000494:pharmacology; D007413:Intestinal Mucosa / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D020123:Sirolimus / Q000494:pharmacology*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D007166:Immunosuppressive Agents; D008565:Membrane Proteins; D012333:RNA, Messenger; D016572:Cyclosporine; D001189:Aryl Hydrocarbon Hydroxylases; C465260:Cyp3a2 protein, rat; C465138:Cyp3a23-3a1 protein, rat; D051544:Cytochrome P-450 CYP3A; D020123:Sirolimus