Darunavir unbound concentrations in plasma, not total concentration is the relevant concentration to predict darunavir efficacy in subject of different body mass index

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Pharmacogenetics and immunosuppressive drugs in solid organ transplantation

The transplantation literature includes numerous papers that report associations between polymorphisms in genes encoding metabolizing enzymes and drug transporters, and pharmacokinetic data on immunosuppressive drugs. Most of these studies are retrospective in design, and although a substantial number report significant associations, pharmacogenetic tests are hardly used in clinical practice. One of the reasons for this poor implementation is the current lack of evidence of improved clinical outcome with pharmacogenetic testing. Furthermore, with efficient therapeutic drug monitoring it is possible to rapidly correct for the effect of genotypic deviations on pharmacokinetics, thereby decreasing the utility of genotype-based dosing. The future of pharmacogenetics will be in treatment models in which patient characteristics are combined with data on polymorphisms in multiple genes. These models should focus on pharmacodynamic parameters, variations in the expression of drug transporter proteins, and predictors of toxicity. Such models will provide more information than the relatively small candidate gene studies performed so far. For implementation of these models into clinical practice, linkage of genotype data to medication prescription systems within electronic health records will be crucial

Multidrug Resistance-Associated Protein 2 (MRP2/ABCC2) Haplotypes Significantly Affect the Pharmacokinetics of Tacrolimus in Kidney Transplant Recipients

BACKGROUND AND OBJECTIVE: Tacrolimus is an immunosuppressive drug used for the prevention of the allograft rejection in the kidney allograft recipients. It exhibits a narrow therapeutic index and a large pharmacokinetic variability. Tacrolimus is mainly metabolized by cytochrome P450 (CYP) 3A4 and 3A5, and effluxed via ATP-binding cassette (ABC) transporters such as P-glycoprotein (P-gp), encoded by ABCB1 gene. The influence of CYP3A5*3 on the pharmacokinetics of tacrolimus has been well characterized. On the other hand, the contribution of polymorphisms in other genes is controversial. In addition, the involvement of other efflux transporter than P-gp in tacrolimus disposition is uncertain. The present study was designed to investigate the effects of genetic polymorphisms of CYP3As and efflux transporters on the pharmacokinetics of tacrolimus. SUBJECTS AND METHODS: A total of 500 blood concentrations of tacrolimus from 102 adult stable kidney transplant recipients were included in the analyses. Genetic polymorphisms in CYP3A4 and CYP3A5 genes as well as the genes of efflux transporters including P-gp (ABCB1), multidrug resistance-associated protein (MRP2/ABCC2) and breast cancer resistance protein (BCRP/ABCG2) were genotyped. For ABCC2 gene, haplotypes were determined as follows: H1 (wild type), H2 (1249G>A), H9 (3972C>T) and H12 (−24C>T and 3972C>T). Population pharmacokinetic analysis was performed using nonlinear mixed effects modeling. RESULTS: Analyses revealed that CYP3A5 expressers (CYP3A5*1 carriers) and MRP2 high activity group (ABCC2 H2/H2 and H1/H2) decreased the dose-normalized trough concentration of tacrolimus by 2.3-fold (p<0.001) and 1.5-fold (p=0.007), respectively. The pharmacokinetics of tacrolimus was best described using a two-compartment model with first order absorption and an absorption lag time. In the population pharmacokinetic analysis, CYP3A5 expressers and MRP2 high activity groups were identified as the significant covariates for tacrolimus apparent clearance expressed as 20.7 × (Age/50)(−0.78) × 2.03 (CYP3A5 expressers) × 1.40 (MRP2 high activity group). No other CYP3A4, ABCB1 and ABCG2 polymorphisms were associated with the apparent clearance of tacrolimus. CONCLUSIONS: This is the first report that MRP2/ABCC2 has crucial impacts on the pharmacokinetics of tacrolimus in a haplotype specific manner. Determination of ABCC2 as well as CYP3A5 genotype may be useful for more accurate tacrolimus dosage adjustment