The influence of pharmacogenetics on the time to achieve target tacrolimus concentrations after kidney transplantation

Previously, we reported that, at 3 months after renal transplantation, individuals with CYP3AP1 genotype CYP3AP1*1 (linked to CYP3A5*1 and strongly associated with expression of CYP3A5) required twofold higher doses of tacrolimus to achieve target blood concentrations than individuals with the genotype CYP3AP1*3/*3 (CYP3A5 nonexpressors). This study assesses the relationship between concentration-controlled dosing during the early period after transplantation, the time to achieve target concentrations and genotype in 178 renal transplant recipients (CYP3AP1*1/*3 or *1/*1: n=53, CYP3AP1*3/*3: n=125). Patients with CYP3AP1*1/*3 or *1/*1 had lower mean tacrolimus concentrations during the first week (Median 13.5 vs. 18.5 mug/L, p<0.0001) with significant delay in achieving target concentrations (15-20 mu g/L during week 1, then 10-15 mu g/L). More CYP3AP1*3/*3 patients had tacrolimus concentrations above target during the first week (73.6% vs. 35.8%, p=0.003). There was no difference in the rate of biopsy-confirmed acute rejection, but rejection occurred earlier in the CYP3AP1*1/*3 or *1/*1 group (median 7 d vs. 13 d, p=0.005). In conclusion, an initial dosing regimen for tacrolimus based on knowledge of the CYP3AP1 genotype and subsequently guided by concentration measurements has the potential to increase the proportion of patients achieving target blood concentrations early after transplantation.