The effect of CYP3A5 and ABCB1 single nucleotide polymorphisms on tacrolimus dose requirements in Caucasian liver transplant patients

Background: Tacrolimus is a substrate of cytochrome P-450 (CYP) 3A enzyme and of the drug transporter ABCBl. We have investigated the effects of possible relevant CYP3A5 and ABCBl single nucleotide polymorphisms (SNPs) present in both donors and recipients on tacrolimus blood levels achieved in a population of 32 Caucasian liver transplant patients. Material/Methods: At 1, 3 and 6 months after transplantation, tacrolimus doses (mg/kg/day) and trough blood levels (C0) were determined. Polymerase chain reaction followed by restriction fragment length polymorphism analysis was used for gen-otyping CYP3A5*3 [6986A>G] as well as ABCBl at exons 21 [2677G>T] and 26 [3435C>T]. Results:87.5% of the population showed a CYP3A5*3/*3 genotype. For the ABCBl SNPs, in the case of 3435C>T the total frequency observed for the allelic variant was 50%. For the 2677G>T, the total frequency of the allelic variant was 12.5%, lower than in other Caucasian populations and without any significant linkage with 3435C>T. At 3 and 6 months after transplantation, tacrolimus dose requirements were significantly higher in patients receiving a liver with one copy of the *1 al-lele compared to those homozygous for the *3 allele (0.111±0.057 vs. 0.057±0.030 [P<0.05] at 3 month and 0.086±0.051 vs. 0.044±0.025 [P<0.05] at 6 month). For the recipients' genotypes, the presence of at least one *1 copy tended, though not statistically significantly, to increase tacrolimus doses. With regard to the ABCBl SNPs, they did not show any influence on tacrolimus dosing requirements. Conclusions: Pharmacogenetic analysis of CYP3A5 in the donor could contribute to determine the appropriate initial dosage of tacrolimus in liver transplant patients