In pediatric recipients, however, it is difficult to perform frequently blood samplings for measurement. Therefore, it is very important to investigate the relationship of CYP3A5 genotyping with TAC pharmacokinetics for establishing a personalized dosage regimen including the initial, the induction and the maintenance doses. In this study, the general consistency in the concept that CYP3A5 expressor requires higher TAC doses than nonexpressor to reach target trough concentrations strongly suggests that CYP3A5 genotyping not only in recipient but also in donor is necessary for establishing a personalized dosage regimen in pediatric liver transplant patients. In addition, we didn’t find any significant impact of ABCB1 and ACE SNPs on TAC disposition. Although a recent study suggested a safer dosing and monitoring of TAC coadministered with rabeprazole early on after liver transplantation regardless of CYP3A5 genotypes of recipients and their donors, our finding in this study is important as it emphasizes the combined effects of recipient’s and donor’s genetic variation in relation to TAC disposition. Moreover, although primary outcome time focused on the early postoperative period in most studies, we set one year of primary outcome time. It is necessary, we think, because impact on recipients, especially for pediatric liver transplant patients, will be long time period because of immunosuppressive regimen for his whole life. TAC is characterized by narrow therapeutic index and interindividual variability in its exposure, and achieving target therapeutic level is difficult, especially during the early period of transplantation. Therefore, the TAC dosing regimens require a regular drug monitoring system based on its trough blood concentration. On the other hand, TAC blood concentration is GS-5734 AbMole monitored to allow therapeutic levels to be maintained, to avoid toxicity and to improve efficacy. In general, post-operative infections were considered as over-immunosupressive, which needs to reduce the dose of TAC, whereas acute cellular rejection was considered as under-immunosupressive, which needs to increase the dose of TAC. But the former needs to exclude the ordinary post-operative infections. Although the same initial TAC dose and the same early induction dose were used, we were surprised to find a CYP3A5 genotype effect so early after transplant, in which the C/D ratio was significantly higher in nonexpressor than expressor on day 3. For pediatric liver recipients, in contrast, another study claimed that they did not identify any relationship between recipient CYP3A5 genotype and TAC dosing. They supposed that the main reason for this lack of association was probably that variations in TAC deposit are largely.