Genotype-guided tacrolimus dosing in African American kidney transplant recipients

Tacrolimus is dependent on CYP3A5 enzyme for metabolism. Expression of the CYP3A5 enzyme is controlled by several alleles including CYP3A5*1, CYP3A5*3, CYP3A5*6 and CYP3A5*7. African Americans (AA) have on average higher tacrolimus dose requirements than Caucasians; however, some have requirements similar to Caucasians. Studies in AA have primarily evaluated the CYP3A5*3 variant; however, there are common nonfunctional variants in AA (CYP3A5*6 and CYP3A5*7) which do not occur in Caucasians. These variants are associated with lower dose requirements and may explain why some AA are metabolically similar to Caucasians. We created a tacrolimus clearance model in 354 AA using a development and validation cohort. Time posttransplant, steroid and antiviral use, age, CYP3A5*1, *3, *6 and *7 alleles were significant towards clearance. This study is the first to develop an AA specific genotype-guided tacrolimus dosing model to personalize therapy.