Tacrolimus is a calcineurin inhibitor widely used for the prevention of allograft rejection in solid organ and bone marrow transplantation. It is characterized by a narrow therapeutic index and large inter-individual pharmacokinetic variability. Adoport® is an immediate-release formulation of tacrolimus, to be administered twice daily. Because of a narrow therapeutic window and a better correlation between pre-dose level and effects than between dose and effect, therapeutic drug monitoring (TDM) based on trough whole blood tacrolimus concentrations is recommended for Adoport®. TDM helps to minimize the risk of acute rejection and the occurrence of adverse effects (mainly nephrotoxicity and, to a lesser extent, neurotoxicity). As reported in a consensus document from a consortium of European experts on tacrolimus TDM, the interdose area-under-the curve (AUC0-12h) is expected to be the best marker of tacrolimus exposure. However, tacrolimus monitoring based on full AUC0-12h is difficult to set up in routine, due to clinical constraints and the necessity of multiple samples. Calculation of the AUC0-12h using Bayesian estimation and a limited sampling strategy, i.e. a few blood samples collected during the early phase post-dose would represent an elegant solution, as already done for other tacrolimus formulations. Furthermore, the pharmacokinetics (PK) of tacrolimus is influenced by a single nucleotide polymorphism within intron 3 of cytochrome P450 3A5 (CYP3A5). Patients who carry at least one CYP3A5\*1 allele are considered to be CYP3A5 expressors (about 12% of the Caucasian population, Hapmap project) and thus require a 1.5 to 2-fold higher starting dose than CYP3A5\*3/\*3 carriers to reach the predefined target exposure early after transplantation. Although this polymorphism showed no impact on the performance of the Bayesian estimators previously developed for other tacrolimus formulation, the patient status for CYP3A5\*3 will be considered in this pharmacokinetic study as a potential covariate in, or confounding factor of, the PK model. Specifically, owing to a 12% frequency in the White European population, about 4 patients carriers of the CYP3A5\*1 allele are expected in this study; the performance of the PK model and Bayesian estimator developed will be specifically evaluated in this subgroup.
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Tacrolimus bayesian estimator performance
Timeframe: Month 3