title: The effect of trimethoprim on CYP2C8 mediated rosiglitazone metabolism in human liver microsomes and healthy subjects.
abstract: OBJECTIVE
  Rosiglitazone, a thiazolidinedione antidiabetic medication used in the treatment of Type 2 diabetes mellitus, is predominantly metabolized by the cytochrome P450 (CYP) enzyme CYP2C8. The anti-infective drug trimethoprim has been shown in vitro to be a selective inhibitor of CYP2C8. The purpose of this study was to evaluate the effect of trimethoprim on the CYP2C8 mediated metabolism of rosiglitazone in vivo and in vitro.
  
  
  METHODS
  The effect of trimethoprim on the metabolism of rosiglitazone in vitro was assessed in pooled human liver microsomes. The effect in vivo was determined by evaluating rosiglitazone pharmacokinetics in the presence and absence of trimethoprim. Eight healthy subjects (four men and four women) completed a randomized, cross-over study. Subjects received single dose rosiglitazone (8 mg) in the presence and absence of trimethoprim 200 mg given twice daily for 5 days.
  
  
  RESULTS
  Trimethoprim inhibited rosiglitazone metabolism both in vitro and in vivo. Inhibition of rosiglitazone para-hydroxylation by trimethoprim in vitro was found to be competitive with apparent K(i) and IC(50) values of 29 microm and 54.5 microm, respectively. In the presence of trimethoprim, rosiglitazone plasma AUC was increased by 31% (P = 0.01) from 2774 +/- 645 microg l(-1) h to 3643 +/- 1051 microg l(-1) h (95% confidence interval (CI) for difference 189, 1549), and half-life was increased by 27% (P = 0.006) from 3.3 +/- 0.5 to 4.2 +/- 0.8 h (95% CI for difference 0.36, 1.5). Trimethoprim reduced the para-O-sulphate rosiglitazone/rosiglitazone and the N-desmethylrosiglitazone/rosiglitazone AUC(0-24) ratios by 22% and 38%, respectively.
  
  
  CONCLUSIONS
  These results indicate that trimethoprim is a competitive inhibitor of CYP2C8-mediated rosiglitazone metabolism in vitro and that trimethoprim administration increases plasma rosiglitazone concentrations in healthy subjects.
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy, University of Pittsburgh, PA, USA.
authors.forename: M W
authors.initials: MW
authors.lastname: Hruska
authors.forename: J A
authors.initials: JA
authors.lastname: Amico
authors.forename: T Y
authors.initials: TY
authors.lastname: Langaee
authors.forename: R E
authors.initials: RE
authors.lastname: Ferrell
authors.forename: S M
authors.initials: SM
authors.lastname: Fitzgerald
authors.forename: R F
authors.initials: RF
authors.lastname: Frye
mesh_terms: D000328:Adult; D000892:Anti-Infective Agents, Urinary / Q000494:pharmacology*; D001189:Aryl Hydrocarbon Hydroxylases / Q000037:antagonists & inhibitors*; D018592:Cross-Over Studies; D065727:Cytochrome P-450 CYP2C8; D005260:Female; D005838:Genotype; D006801:Humans; D007004:Hypoglycemic Agents / Q000378:metabolism*; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism*; D000077154:Rosiglitazone; D045162:Thiazolidinediones / Q000037:antagonists & inhibitors*; D014295:Trimethoprim / Q000494:pharmacology*
chemical_list: D000892:Anti-Infective Agents, Urinary; D007004:Hypoglycemic Agents; D045162:Thiazolidinediones; D000077154:Rosiglitazone; D014295:Trimethoprim; D001189:Aryl Hydrocarbon Hydroxylases; C450259:CYP2C8 protein, human; D065727:Cytochrome P-450 CYP2C8