Aims To evaluate the effect of corticosteroids on tacrolimus pharmacokinetics. Methods In a randomized trial, kidney transplant recipients were treated with tacrolimus and mycophenolate mofetil with either daclizumab ( n = 31) or 3 months of prednisone ( n = 34). Tacrolimus dose-adjusted predose concentrations ( C 0 ) at month 1-6 were compared between both groups and within the corticosteroid group before and after prednisone withdrawal. Results At month 1 the tacrolimus dose-adjusted C 0 in the corticosteroid group was 83 ± 8 vs 119 ± 17 ng ml -1 mg -1 kg -1 in the daclizumab group. The tacrolimus doseadjusted C 0 within the corticosteroid group at month 1 and 2 was 42% and 29% lower compared with month 4 ( P < 0.001). Conclusions A higher tacrolimus dose is required to reach target concentrations when used in combination with corticosteroids.

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