[Pharmacogenetics of tacrolimus: from bench to bedside?].

Tacrolimus (FK-506) is an immunosuppressant widely used to prevent kidney transplant rejection. Patients receive an initial standard dose and tacrolimus levels are measured in blood. If necessary, the dose is adjusted to reach a blood concentration within the accepted range. There is great interindividual variability in the dose required to achieve the target blood level, and many patients require multiple modifications of the dose to reach the range. One of the main determinants of these differences is a CYP3A5 gene polymorphism that determines that about 80% of Caucasians are poor metabolisers and require lower doses compared to the extensive metabolisers. It has been proposed that transplanted patients could receive an initial Tacrolimus dose based on the CYP3A5 genotype. This could reduce the time to achieve the optimal blood level, reducing the number of dose modifications. However, to be accepted by clinicians and translated to the clinical practice this adapted dose procedure should give additional advantages such as a significant reduction of the rates of nephrotoxicity and rejection, or a lower cost due to less dose modifications of Tacrolimus and less antibody induction therapy.