 Tacrolimus is the cornerstone immunosuppressant in children with liver transplantation, its use is complicated by its narrow therapeutic index and variable pharmacokinetics. Therapeutic drug monitoring TDM of tacrolimus, based on whole-blood trough concentration C0 values, is mandatory for use of twice-daily tacrolimus Prograf_ as in order to decrease interindividual variability in exposure and thereby minimize the risk of acute rejection and the occurrence of adverse effects mainly nephrotoxicity and, to a lesser extent, neurotoxicity. 