Tacrolimus in Pediatric Solid Organ Transplant Recipients: A Retrospective Cohort Study

BACKGROUND: Tacrolimus is an effective immunosuppressant used after transplantation to prevent organ rejection. Standard tacrolimus dosing relies on therapeutic drug monitoring and does not account for patient-specific factors, contributing to substantial inter-individual variability. In this retrospective study, tacrolimus target attainment and intra-patient variability under standard care were investigated in pediatric solid organ transplant recipients. METHODS: In a cohort of 39 kidney, 31 liver, 48 heart, and 1 liver-kidney transplant recipients, tacrolimus trough concentrations from days 4 to 56 post-initiation of tacrolimus were analyzed. Time in target range (TTR) and intra-patient variability (coefficient of variation) were calculated over the 8-week period. Secondary outcome analyses examined associations between TTR and clinical outcomes. RESULTS: Across all groups, target attainment was lowest on day 4 and improved by days 21 and 56, but remained suboptimal, particularly among liver recipients (day 56: Heart 45%, kidney 76%, liver 31%). Average TTR was highest in the kidney (60%) and lowest in the liver recipients (27%), with only 3% of liver recipients spending at least half of the time within the target. CONCLUSIONS: Standard tacrolimus dosing often results in out-of-target exposure, with particularly poor target attainment and high variability among pediatric liver transplant recipients. These findings highlight the limitations of current approaches and support the need for more individualized strategies, including genotype-guided dosing, to improve target attainment and outcomes in pediatric transplant recipients.