Influence of different formulations of tacrolimus on dosage regimen and drug exposure within the first year after kidney transplantation

Introduction: Two most common pharmaceutical formulation of tacrolimus (Tac) used after kidney transplantation (Tx) are immediate-release one, administered twice-daily (TacTD), and prolonged-release one, administered once-daily (Tac-OD). Aim: The aim of this study was to compare daily doses, trough concentrations (C0 ) and dose-adjusted trough concentrations (C0 /D) of Tac between patients who administered different drug formulations, Tac-TD or Tac-OD, during the first year after Tx. Additionally, the aim of the study was to compare the distribution of C0 within and beyond the target therapeutic range (8-12 ng/mL for the first 90 days and 6-10 ng/mL afterwards) after the administration of different drug formulations. Subjects and Methods: A retrospective pharmacokinetic study included 84 patients (56 on Tac-TD and 28 on Tac-OD), with a follow-up period between the first and twelfth month post-transplantation. Following pharmacokinetic data were used: daily dose, daily dose according to patient's body weight, concentration C0 and C0 /D of Tac. Results: The results of the study showed that patients on Tac-OD formulation had higher daily doses and higher C0 during 4-6 months (p<0.01) and 7-12 months (p<0.01) after Tx. Patients on Tac-OD had lower C0 /D during 4-6 months (p<0.05) and 7-12 months (p<0.01) after Tx. C0 in Tac-TD patients was significantly more frequently below the target range, whereas in Tac-OD patients C0 was more frequently above the target range, while both patient groups had equal distribution of C0 within the target range of Tac in the period between 4th and 12th month post-transplantation (p<0.01). Conclusions: The conducted research suggests that patients on Tac-OD preparation may require higher daily doses of Tac compared to patients on Tac-TD preparation in order to maintain optimal immunosuppression in the late post-transplant period.