Pre-transplant tacrolimus fluctuations predict BK virus infection risk in kidney transplants

BackgroundBK virus (BKV) infection is a significant complication in kidney transplant recipients, potentially leading to graft loss. The relationship between pre-transplant tacrolimus (TAC) pharmacokinetics and BKV infection risk remains unclear. This study aimed to investigate whether pre-transplant TAC blood concentration fluctuations are associated with BKV infection risk.MethodsWe conducted a retrospective study of 135 living donor kidney transplant recipients at Hirosaki University between 2006 and March 2024. Patients were divided into BKV-infected (BKV) and non-infected (non-BKV) groups. TAC blood concentrations were measured at 4 points, including 0 h (2 h before TAC administration), 4, 6, and 12 h on the day before transplantation. Changes in TAC concentration from baseline (0 h) were calculated for each time point. The concentration/dose (C0/D) ratio was used as an indicator of TAC metabolism rate.ResultsDuring a median follow-up of 54 months, 29 recipients developed BKV infection. The BKV group had significantly older donors and showed a significantly larger decrease in TAC concentration at 12 h compared to the non-BKV group (-1.5 vs. 0 ng/mL, P = 0.008). There was no significant difference in pre-transplant C0/D ratios between the two groups. A decrease of >= 1.5 ng/mL at 12 h was identified as a significant risk factor for BKV infection (hazard ratio: 2.44, 95% confidence interval: 1.11-5.32, P = 0.026) in a propensity score-based inverse probability of treatment weighting multivariate Cox proportional hazards analysis.ConclusionPre-transplant TAC blood concentration fluctuations, particularly a large decrease at 12 h from baseline, may be associated with increased BKV infection risk.