BACKGROUNDRecent studies have identified new candidate polymorphisms in the genes related to CYP3A activity or calcineurin inhibitor dose requirements in kidney transplant recipients. These genes and polymorphisms are CYP3A4 (cytochrome P450, family 3, subfamily A, polypeptide 4) (rs35599367-C>T; *22); POR [P450 (cytochrome) oxidoreductase] (rs1057868-C>T; *28); and PPARA (peroxisome proliferator-activated receptor alpha) (rs4253728-G>A). We investigated the impact of these polymorphisms on sirolimus (SRL) in vitro hepatic metabolism, SRL trough concentrations (C0), and SRL adverse events in kidney transplant recipients.METHODSThe clinical study included 113 stable kidney transplant patients switched from a calcineurin inhibitor to SRL (SRL C0 measured at 1, 3, and 6 months thereafter). We investigated SRL metabolism in vitro using human liver microsomes derived from individual donors (n = 31). Microsomes and patients were genotyped by use of Taqman® allelic discrimination assays. The effects of polymorphisms and covariates were studied using multilinear regression imbedded in linear mixed-effect models or logistic regressions.RESULTSIn vitro, the CYP3A4*22 allele resulted in approximately 20% lower metabolic rates of SRL (P = 0.0411). No significant association was found between CYP3A4, CYP3A5, or PPARA genotypes and SRL dose, C0, or C0/dose in kidney transplant patients. POR*28 was associated with a minor but significant decrease in SRL log-transformed C0 [CT/TT vs CC, β = −0.15 (0.05); P = 0.0197] but this did not have any impact on the dose administered, which limited the relevance of the finding. After adjustment for nongenetic covariates and correction for false discovery finding, none of the single-nucleotide polymorphisms tested showed significant association with SRL adverse events.CONCLUSIONSThese recently described polymorphisms do not seem to substantially influence the pharmacokinetics of SRL or the occurrence of SRL adverse events in kidney transplant recipients.