Conversion From a Twice-Daily to a Once-Daily Tacrolimus Formulation in Kidney Transplant Recipients

Background. The aim of the study was to assess bioavailability aspects of tacrolimus formulations during conversion from twice-daily (TAC BID) to once-daily (TAC OD) formulation in 89 stable kidney transplant recipients. Materials and Methods. The study included 89 stable kidney transplant recipients transplanted between 1998 and 2008 (37 female, 52 male, aged 46.0 +/- 12.4 years) and followed for 10 years. For a comprehensive comparison of the different tacrolimus formulations, dose-normalized trough levels (ng/mL/mg total daily dose, C/D ratio) and their variability were studied for 10 consecutive visits before and 6 months after conversion. Results. The mean trough level decreased significantly 14 days after conversion (16%, 5.77 +/- 1.94 [5.6, 4.5-6.5] ng/mL, P < .001). There was no significant difference between the tacrolimus trough levels before and 3 months after conversion (6.92 +/- 1.89 [6.8, 5.9-8.0] ng/mL, P = .548). The tacrolimus daily dose 3 months after conversion (4.56 +/- 1.81 [4.5, 3.5-5.5] mg/d) was significantly higher than the dose before conversion (4.16 +/- 1.80 [4.0, 3.0-5.0] mg/d, P = .006). The post-conversion mean TAC trough level (10 measures) (6.6 [6.2-7.0] ng/mL) was similar to preconversion level (6.8 [5.6-7.9] ng/mL, P = .203). C/D ratio as well as C/D intrapatient variability (CV%) did not change during conversion (C/D 1.68 [1.36-2.53] vs 1.74 [1.41 vs 2.31], P = .075; CV% 19.5 [16.4-26.6] vs 24.4 [17.5-28.3], P = .114). Conclusions. Conversion from TAC BID to TAC OD is associated with a significant increase in tacrolimus dose during the first 3 months. In a long-term observation both formulations present similar dose-normalized trough levels and variability.