A Simple Novel Technique to Estimate Tacrolimus Dosages During the Early Post Kidney Transplantation Period

Abstract Background Tacrolimus pharmacokinetics prediction by CYP3A5 genotyping is not available in many Asian resource-limited settings. Therefore, an alternative technique is needed to estimate the dose of tacrolimus perioperatively. The 12-hour level after the first dose (C12-0) is an alternative technique for estimating the dose of tacrolimus. This simple and inexpensive calculation technique can be used by any transplantation center. Methods A prospective study on a cohort of 57 incident post-kidney transplant recipients was conducted. The whole-blood tacrolimus trough level (C12-0) was measured at 12 hours after the first dose (0.1 mg/kg) of orally administered tacrolimus during transplantation. Concomitant medications with CYP3A5 inhibitors/inducers were not allowed. Genotyping for CYP3A5 expression was carried out by reverse transcription polymerase chain reaction. The dosages and trough levels of tacrolimus at postoperative day 7 and postoperative months 1 to 3 were measured and analyzed for the dose requirements for therapeutic levels (mg/kg/d). Results The doses of tacrolimus were widely diverse, ranging from 0.049 to 0.260 mg/kg/d and 0.031 to 0.298 mg/kg/d at day 7 and months 1 to 3, respectively. There were 9, 28, and 20 patients (15.8%, 49.1%, and 35.1%) with CYP3A5 *1/*1 , *1/*3 , and *3/*3 , respectively. The CYP3A5 genotypes were significantly correlated with the target tacrolimus dose at day 7 (r2 = 0.307) and the stable dose at months 1 to 3 (r2 = 0.337). The C12-0 level also was significantly correlated with the dose of tacrolimus at day 7 (r2 = 0.546) and the stable dose at months 1 to 3 (r2 = 0.406). Conclusions There were strong correlations between the C12-0 level and the tacrolimus doses during the perioperative period at day 7 and the stable period at 1 to 3 months. Countries with limited resources for genotype testing can use the C12-0 level as an alternative to estimate the tacrolimus dose.