Association between time in therapeutic range of tacrolimus blood concentration and acute rejection within the first three months after lung transplantation

Background Tacrolimus is a key drug in immunosuppressive therapy following lung transplantation. The blood tacrolimus levels are likely to fluctuate in the early postoperative period, and failure to maintain the tacrolimus trough level in target ranges is a risk factor for rejection. However, there is little information about the relationship between the time in therapeutic range (TTR) of the tacrolimus trough level (tacrolimus TTR) and clinical outcomes. This study aimed to evaluate the association between tacrolimus TTR and acute rejection (AR) within the first three months after lung transplantation. Methods This was a retrospective study of patients who underwent lung transplantation at a single center. The target tacrolimus trough levels were 10–15 ng/mL, and tacrolimus TTR was calculated using the Rosendaal method. The cut-off value of the tacrolimus TTR was estimated by receiver operating characteristic analysis based on AR. Results The study included 90 patients. AR was observed in 26 patients. In this study, ‘‘early-AR’’ was defined as any AR within 2 weeks post-transplant ( n = 22) and ‘‘late-AR’’ was defined as any AR after 1-month post-transplant ( n = 4). For early AR, the relationship between tacrolimus TTR and the onset of AR was examined. There were no differences in the tacrolimus TTR between the early-AR group and non-AR group (35.7 ± 22.4 vs 31.5 ± 19.9%, P = 0.416). For late-AR, the relationship with tacrolimus TTR was examined every 10 d. The tacrolimus TTR during postoperative days (POD) 21–30 and POD 31–onset was significantly lower in the late-AR group than the no-AR group (50.0 ± 7.1 vs. 71.8 ± 18.0% and 37.0 ± 26.6 vs. 68.9 ± 31.5%, P < 0.05, respectively). The cutoff value of the tacrolimus TTR during POD 21–30 was estimated as 55.0%. Conclusions Our findings suggest that a lower tacrolimus TTR is a predictor of late AR. A tacrolimus TTR of 55% or higher is necessary to reduce the risk of AR during this period after lung transplantation.