Pharmacogenomic/pharmacokinetic assessment of a four-probe cocktail for CYPs and OATPs following oral microdosing.

OBJECTIVES: To test whether the multiple phenotype and genotype relationships established using therapeutic dose, can be reproduced following oral microdosing using substrates of CYP2C9 (warfarin and glibenclamide), CYP2C19 (lansoprazole), CYP2D6 (dextromethorphan), and OATPs (glibenclamide). METHODS: A cocktail of test drugs was administered orally under the microdose in liquid or capsule form, and then a therapeutic dose of dextromethorphan was administered to 17 healthy subjects whose genotypes for CYPs and OATPs had been prescreened. Concentrations of the drugs and their metabolites were measured by LC-MS/MS. RESULTS: The AUC and t1/2 of glibenclamide following the microdosing tended to be higher and longer, respectively, in CYP2C9*1/*3 than CYP2C9*1/*1 subjects. In contrast, there were no significant differences in any of the pharmacokinetic parameters for warfarin between the two genotypes. For CYP2D6 following the therapeutic dose, there was good concordance between genotype and phenotype; however, such relationships disappeared after microdosing. For CYP2C19 following the microdosing, there were significant differences between EMs and PMs in the pharmacokinetic parameters of lansoprazole. The relative AUC0-12 ratio of lansoprazole in EMs and PMs was 1:3.3 - 4.3. Among test drugs, phenotypic measurements of lansoprazole accorded well with the CYP2C19 genotype at the microdose as well as therapeutic dose. CONCLUSIONS: The present study suggests that 1) the sampling strategy should be optimized according to pharmacokinetic profiles of the test drugs following oral microdosing, and 2) microdosing can be applied to the pharmacogenomic study of CYP-specific drugs.

Role of methotrexate polyglutamation and reduced folate carrier 1 (RFC1) gene polymorphisms in clinical assessment indexes.

The aims of the present study were to define inter-individual differences in response to methotrexate (MTX) through MTX polyglutamate (MTX-PG) levels in red blood cells (RBC) and MTX-related gene polymorphisms. A total of 145 rheumatoid arthritis patients were recruited. MTX-PG1-5 concentrations in RBC were measured, and 11 single nucleotide polymorphisms, all in MTX-related genes involved in the folate pathway, were analyzed. Disease activity was also assessed. There was no direct relationship between any MTX-PG concentration and the patient's disease condition, but detectability of MTX-PG5 was extracted as a candidate marker for response to MTX. When disease activity was compared between patients in which MTX-PG5 was detectable and undetectable, all indexes except the visual analog scale (VAS) and C-reactive protein (CRP) were found to be significantly lower in the former patients. Reduced folate carrier 1 (RFC1) 80G>A was significantly associated with the detectability of MTX-PG5; detectability of MTX-PG5 was lower in patients with the A mutant allele. The present study suggests that detectability of MTX-PG5 in RBC is a possible biomarker for response to MTX, and the RFC1 80G>A mutation is associated with low detectability of MTX-PG5. Prospective studies with a sufficient number of patients are needed to confirm the present findings.

Mechanisms of pharmacokinetic enhancement between ritonavir and saquinavir; micro/small dosing tests using midazolam (CYP3A4), fexofenadine (p-glycoprotein), and pravastatin (OATP1B1) as probe drugs.

We investigated the mechanisms of ritonavir-mediated enhancement effect on the pharmacokinetics of saquinavir using in vivo probes for CYP3A4 (midazolam), p-glycoprotein (fexofenadine), and OATP1B1 (pravastatin) following oral micro/small dosing. A cocktail of the drugs (2 mg of saquinavir, 100 µg of each probe) was administered to eight healthy volunteers (phase 1), and then coadministered with 20 mg (phase 2) and 100 mg (phase 3) of ritonavir. Plasma concentrations of the drugs were measured by validated LC-MS/MS methods. The mean plasma AUC0-24 (pg hour/mL) of saquinavir at phases 1, 2, and 3 was 101, 2 540, and 23 900 (P < .01), respectively. The relative area under the plasma concentration-time curve (AUC)0-24 ratios of midazolam and fexofenadine at phases 1, 2, and 3 were 1:5.9:14.7 (P < .01), and 1:1.4:2.2 (P < .01-.05), respectively. In contrast, there was no difference in the pharmacokinetics of pravastatin. Inhibition of intestinal and hepatic CYP3A-mediated metabolism, and intestinal p-glycoprotein-mediated efflux of saquinavir, but not OATP1B1, is involved in the enhancement mechanism. Micro/small dosing is useful for examining the mechanism of drug interactions without safety concern.

Pre-administration of docetaxel protects against adriamycin-induced cardiotoxicity.

BACKGROUND: We have revealed in a pre-clinical study that the combination of adriamycin (ADR) and docetaxel (DOC) in which ADR was administered 12 h after DOC injection not only significantly reduced leukopenia and toxic death but also significantly increased the antitumor effect compared with the dosing schedule without an interval between each injection used commonly in clinical practice. The purpose of this study was to clarify in mice whether the toxic death caused by ADR was reduced by administering ADR after DOC injection when the doses and dosing-interval of ADR and DOC were changed. METHODS: ADR alone or a combination of ADR and DOC (ADR/DOC group in which both drugs were administered simultaneously or DOC-ADR group in which ADR was administered after DOC injection) was administered every 7 days in mice. RESULTS: When dosing intervals (0-24 h) were changed, there were no differences in survival rate among the 6, 12, and 24-h interval groups, although these groups showed significantly higher survival rate compared with the ADR/DOC group. When the dose of ADR (2.5-15 mg/kg) was changed, the survival rate was higher in all the DOC-ADR groups than the ADR alone groups. When the dose of DOC (3.125-12.5 mg/kg) was changed, DOC caused a dose-dependent reduction in toxic death. Although there was no striking difference in adverse effects between the ADR alone and DOC-ADR groups, the DOC-ADR group showed markedly attenuated increases in CPK-MB activity compared with the ADR alone group. CONCLUSIONS: We conclude that pre-administration of DOC may protect against ADR-induced toxic death and cardiotoxicity.