The impact of tacrolimus variability on first year renal function in kidney transplant recipients: A retrospective cohort study.

Tacrolimus is a key immunosuppressant with a narrow therapeutic range in kidney transplantation. Early fluctuations in trough concentrations may influence graft stability, yet the clinical significance of early intrapatient variability remains uncertain. This study aimed to evaluate whether tacrolimus variability during the first posttransplant month is associated with renal function at 12 months. This single-center retrospective cohort study included adult kidney transplant recipients receiving tacrolimus-based immunosuppression between January 2017 and December 2021. Tacrolimus variability was quantified as the absolute difference (Δ, ng/mL) between maximum and minimum trough concentrations during the first 30 days, classified as high (Δ > 8 ng/mL) or low (Δ ≤ 8 ng/mL). Renal function was assessed using eGFR at 1, 3, 6, and 12 months. Statistical analyses applied appropriate parametric and nonparametric tests with a significance level of P < .05. High variability was associated with more frequent subtherapeutic and supratherapeutic trough concentrations and transient reductions in early graft performance. However, 12-month eGFR was not significantly different between variability groups. In multivariable models, recipient age, donor age, and biopsy-proven graft dysfunction were consistently associated with lower eGFR across follow-up. Male donor sex showed a positive association with eGFR only at 6 months, whereas early tacrolimus variability was not independently associated with eGFR at any time point.