Quantitation of the impact of CYP3A5 A6986G polymorphism on quetiapine pharmacokinetics by simulation of target attainment.

The aim of this study was to evaluate whether genetic polymorphisms in CYP3A5 and ABCB1 are responsible for the interindividual variability observed in quetiapine pharmacokinetics. Pharmacokinetic data from a randomized crossover study evaluating 2 quetiapine 25 mg immediate-release tablets after single oral dose were used to develop a population pharmacokinetic model. The single nucleotide polymorphisms (SNPs) evaluated for the genotype effects of quetiapine pharmacokinetics were CYP3A5 A6986G and ABCB1 C3435T, along with other demographic variables and formulations. A one-compartment distribution model with linear elimination plus four transit compartments for the delayed absorption adequately described quetiapine disposition. CYP3A5 *1/*1 individuals (n = 3) had 29% increased clearance compared to *1/*3 and *3/*3 individuals. The impact of an increased clearance was evaluated by simulations. By computing the probability of target attainment (PTA) of steady-state therapeutic goal at 1-hour and 12-hour time points after 50-400 mg twice-daily regimens, the results indicated that CYP3A5 genotype has minimal impact on the PTA of the 1-hour concentrations but a significant impact on the 12-hour concentrations. The interpretation based on the simulations does not call for a genotype-based dosing scheme and is consistent with consensus guidelines for quetiapine that therapeutic drug monitoring is considered useful. Clinical Pharmacology in Drug Development.

The impact of CYP3A5 and MDR1 polymorphisms on tacrolimus dosage requirements and trough concentrations in pediatric renal transplant recipients.

Previous international studies demonstrated significant heterogeneity in the tacrolimus (TAC) dose required to attain target blood concentrations, attributed to both genetic and ethnic factors. While the majority of previous reports on adult recipients of renal, heart and liver transplants have shown a significant effect of CYP3A5FNx013 single nucleotide polymorphisms (SNPs) on TAC pharmacokinetics (PKs), the impact of multidrug resistance protein 1 (MDR1) and SNPs remains controversial. Yet, similar data of TAC in pediatric populations, in whom the intra- and inter-subject variations are likely to be even greater, is currently limited. We aimed to examine the influence of various CYP3A5 and MDR1 genotypes on TAC dose requirements and PKs in the Jordanian pediatric renal transplant population. Thirty-eight patients were genotyped for CYP3A5FNx011 and FNx013 and MDR1 C3435T. Dose-adjusted trough concentrations (C 0 /D) and daily doses (D) were compared among different CYP3A5 and MDR1 genotypes in the early and maintenance phases post-transplant. Surprisingly, there were no significant differences in D, C 0 or C 0 /D among the genotypes of CYP3A5 or MDR1 polymorphisms in either the early or the maintenance phase after transplantation, whereas after combining the C 0 /D levels of MDR1 C allele expressers, noticeably lower TAC levels were observed as compared with the TT genotype. However, the difference became not significant beyond 3 months. Based on a pharmacogenetic evaluation, the independent impact of CYP3A5 SNPs on TAC PKs was not evident, demonstrating the need for further large-scale studies.

Influence of CYP3A5 6986A > G and ABCB1 3435C > T Polymorphisms on Adverse Events Associated With Tacrolimus in Jordanian Pediatric Renal Transplant Patients.

The aim of the study is to investigate the influence of ABCB1(3435) and CYP3A5(6986) polymorphisms, tacrolimus troughs and clinical factors on the time of adverse events associated with tacrolimus in pediatric kidney transplant patients. Clinical data, adverse events, tacrolimus troughs, corresponding doses, ABCB1 3435C > T and CYP3A5 6986A > G genotypes were collected from 38 pediatric kidney transplant patients in a retrospective study for over 2 years post-transplant. We used a marginal Cox proportional hazard model to evaluate the influence of clinical factors and single nucleotide polymorphisms (SNPs) on tacrolimus-associated adverse events. CYP3A5 genotype, the Bayesian predicted tacrolimus concentrations, hematocrit and mean corpuscular volume are significant risk factors of adverse events over a 2-year-period. CYP3A5*1 genotype was associated with 36% relative risk of CYP3A5*3/*3 genotype. In the 9-month period, the additional factor, ABCB1 3435TT genotype, was shown to be associated with 38% relative risk of the CC and CT genotypes. For graft loss, acute and chronic rejection, only tacrolimus concentration and hematocrit, but not CYP3A5 or ABCB1 polymorphisms, are important factors influencing their occurrences.