title: Cytochrome P450 3A4 and P-glycoprotein mediate the interaction between an oral erythromycin breath test and rifampin.
abstract: BACKGROUND
  The intravenous (14)C-erythromycin breath test (ERMBT(IV)) does not measure aggregate liver and intestinal cytochrome P450 (CYP) 3A4 activity. Accordingly, we evaluated an oral stable-labeled ((13)C) formulation of the test (ERMBT(oral)) as an alternative CYP3A4 phenotyping probe.
  
  
  METHODS
  After an overnight fast, 14 young healthy volunteers (5 women and 9 men) received the ERMBT(IV) (0.07 micromol, 3 muCi), followed by the ERMBT(oral) (500 mg). The next morning, the CYP3A4 inhibitor troleandomycin (500 mg) was given, and both ERMBTs were repeated. After at least 24 hours, the CYP3A4 and P-glycoprotein inducer rifampin (600 mg; INN, rifampicin) was given daily for 7 days, and both ERMBTs were repeated 24 hours after the last dose of rifampin. Plasma samples were collected for 10 hours with each administration of the ERMBT(oral), and erythromycin levels were measured by liquid chromatography-mass spectrometry. Finally, the effect of troleandomycin on erythromycin transport was examined in Caco-2 cell monolayers.
  
  
  RESULTS
  Compared with baseline values, the median ERMBT(IV) and ERMBT(oral) results and erythromycin apparent oral clearance (CL/F) all significantly decreased, by at least 70%, with troleandomycin treatment (P =.001 for each comparison). With rifampin treatment, the median ERMBT(IV) result and CL/F increased 2-fold (P < or =.01), but the median ERMBT(oral) result was unchanged (P =.30). There were no rank-order correlations between the ERMBT(IV) and ERMBT(oral) results or between either ERMBT result and CL/F within each treatment group (P > or =.07). In addition, troleandomycin had no effect on erythromycin transport in Caco-2 cells (P > or =.20).
  
  
  CONCLUSIONS
  The ERMBT(oral) was influenced by processes in addition to intestinal and hepatic CYP3A4 activity and therefore did not provide a straightforward measure of aggregate CYP3A4 phenotype. The erythromycin-rifampin interaction cannot be attributed to CYP3A4 induction alone and probably also reflected intestinal P-glycoprotein induction.
authors.affiliation: Department of Pharmacology, University of Michigan, Ann Arbor, USA.
authors.forename: Mary F
authors.initials: MF
authors.lastname: Paine
authors.forename: David A
authors.initials: DA
authors.lastname: Wagner
authors.forename: Keith A
authors.initials: KA
authors.lastname: Hoffmaster
authors.forename: Paul B
authors.initials: PB
authors.lastname: Watkins
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000502:physiology*; D000328:Adult; D001692:Biological Transport; D001944:Breath Tests; D002245:Carbon Dioxide / Q000378:metabolism; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology*; D004347:Drug Interactions; D004917:Erythromycin / Q000493:pharmacokinetics*; D005260:Female; D006801:Humans; D008297:Male; D012293:Rifampin / Q000494:pharmacology*; D014217:Troleandomycin / Q000494:pharmacology
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D065607:Cytochrome P-450 Enzyme Inhibitors; D002245:Carbon Dioxide; D004917:Erythromycin; D003577:Cytochrome P-450 Enzyme System; D014217:Troleandomycin; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D012293:Rifampin