These data indicate that St John's wort increases imatinib clearance. Thus patients taking imatinib should avoid taking St John's wort. Concomitant use of enzyme inducers, including St John's wort, may necessitate an increase in the imatinib dose to maintain clinical effectiveness.

Cytidine deaminase (CDA) hydrolytically deaminates and irreversibly deactivates the chemotherapeutic agent cytosine arabinoside (Ara-C), a deoxycytidine analog used for treatment of acute leukemias and lymphomas. To determine if single nucleotide polymorphisms (SNPs) in the promoter region of CDA affected gene expression, we sequenced approximately 1.6 Kb upstream of the CDA translation initiation site and containing the proximal promoter of CDA. We identified 6 SNPs; -92A>G, -205C>G, -451C>T, -897C>A, -1075A>G and -1181G>A. Based on predicted changes in transcription factor binding sites, three SNPs (-92A>G, -451C>T and -897C>A) were chosen for further investigation. The five haplotypes segregating in the population were cloned into a luciferase expression plasmid, transfected into Cos-1 cells and reporter activity measured at 24 and 48 h. Four haplotypes showed an average expression which was 2.5-fold higher at 24 h (P<0.0001) and 3.3-fold higher at 48 h (P<0.0001) than the lowest expressing haplotype. When reanalyzed as single SNP genotypes, the differences in expression were significant, except for -897 C/A, at 24 h, but the magnitude of difference was reduced, suggesting that no single SNP completely accounts for the expression differences observed at the haplotype level. As predicted from the in vitro analysis, individuals homozygous for common haplotype (ACC/ACC) showed higher levels of CDA enzymatic activity as individuals heterozygous for the wild type and low expressing haplotype (ACC/ATC). As CDA promoter region haplotypes may influence Ara-C chemosensitivity, shown here in in vitro and in vivo studies, the clinical relevance of these findings should be examined.

AimsRosiglitazone, a thiazolidinedione antidiabetic medication used in the treatment of Type 2 diabetes mellitus, is predominantly metabolized by the cy tochrome 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 . MethodsThe 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. ResultsTrimethoprim 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 m M and 54.5 m M , respectively. In the presence of trimethoprim, rosiglitazone plasma AUC was increased by 31% ( P = 0.01) from 2774 ± 645 m g l -1 h to 3643 ± 1051 m g 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. ConclusionsThese 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. Effect of Trimethoprim on RosiglitazoneBr J Clin Pharmacol 59 :1 71