title: Role of intestinal P-glycoprotein (mdr1) in interpatient variation in the oral bioavailability of cyclosporine.
abstract: Interpatient differences in the oral clearance of cyclosporine (INN, ciclosporin) have been partially attributed to variation in the activity of a single liver enzyme termed CYP3A4. Recently it has been shown that small bowel also contains CYP3A4, as well as P-glycoprotein, a protein able to transport cyclosporine. To assess the importance of these intestinal proteins, the oral pharmacokinetics of cyclosporine were measured in 25 kidney transplant recipients who each had their liver CYP3A4 activity quantitated by the intravenous [14C-N-methyl]-erythromycin breath test and who underwent small bowel biopsy for measurement of CYP3A4 and P-glycoprotein. Forward multiple regression revealed that 56% (i.e., r2 = 0.56) and 17% of the variability in apparent oral clearance [log (dose/area under the curve)] were accounted for by variation in liver CYP3A4 activity (p < 0.0001) and intestinal P-glycoprotein concentration (p = 0.0059), respectively. For peak blood concentration, liver CYP3A4 activity accounted for 32% (p = 0.0002) and P-glycoprotein accounted for an additional 30% (p = 0.0024) of the variability. Intestinal levels of CYP3A4, which varied tenfold, did not appear to influence any cyclosporine pharmacokinetic parameter examined. We conclude that intestinal P-glycoprotein plays a significant role in the first-pass elimination of cyclosporine, presumably by being a rate-limiting step in absorption. Drug interactions with cyclosporine previously ascribed to intestinal CYP3A4 may instead be mediated by interactions with intestinal P-glycoprotein.
authors.affiliation: Department of Internal Medicine, School of Public Health, University of Michigan, Ann Arbor, USA.
authors.forename: K S
authors.initials: KS
authors.lastname: Lown
authors.forename: R R
authors.initials: RR
authors.lastname: Mayo
authors.forename: A B
authors.initials: AB
authors.lastname: Leichtman
authors.forename: H L
authors.initials: HL
authors.lastname: Hsiao
authors.forename: D K
authors.initials: DK
authors.lastname: Turgeon
authors.forename: P
authors.initials: P
authors.lastname: Schmiedlin-Ren
authors.forename: M B
authors.initials: MB
authors.lastname: Brown
authors.forename: W
authors.initials: W
authors.lastname: Guo
authors.forename: S J
authors.initials: SJ
authors.lastname: Rossi
authors.forename: L Z
authors.initials: LZ
authors.lastname: Benet
authors.forename: P B
authors.initials: PB
authors.lastname: Watkins
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000097:blood / Q000378:metabolism*; D000284:Administration, Oral; D000328:Adult; D000368:Aged; D019540:Area Under Curve; D001682:Biological Availability; D001944:Breath Tests; D016572:Cyclosporine / Q000008:administration & dosage / Q000493:pharmacokinetics*; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000097:blood / Q000378:metabolism*; D004386:Duodenum / Q000378:metabolism; D005260:Female; D006801:Humans; D015151:Immunoblotting; D007166:Immunosuppressive Agents / Q000008:administration & dosage / Q000493:pharmacokinetics*; D016030:Kidney Transplantation; D008099:Liver / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D006899:Mixed Function Oxygenases / Q000097:blood / Q000378:metabolism*; D012044:Regression Analysis
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D007166:Immunosuppressive Agents; D016572:Cyclosporine; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human