The New LC-MS/MS Method for Determination of Unbound Tacrolimus in Plasma

Tacrolimus (TAC) is characterized by a narrow therapeutic window, as well as high inter- and intra-individual variability in pharmacokinetics. Both under- and overexposure may lead to severe adverse effects. Therapeutic drug monitoring (TDM) is an essential element of post-transplant patient care. Most transplantation centers use C0 to adjust TAC dosage. Some controversies remain about relationship between C0 and clinical outcome. It is generally accepted that only protein-unbound drug molecules can cross cellular membranes, which imply that TDM of free tacrolimus fraction may be of paramount importance and improve clinical management of organ recipients. Whole blood TAC concentrations and dose requirements are strongly associated with CYP3A5 polymorphism. Routine CYP3A5 genotyping on the waiting lists might be useful to guide tacrolimus dosing. This interdisciplinary project tackles the research problem from three angles - biochemistry, genetics and clinical observation. The primary goal of the study is to evaluate clinical usefulness of different TDM protocols in patients after kidney and liver transplantation.