*Purpose: The aim of this study was to investigate the association between various pediatric recipient characteristics at time of liver transplant and FK506 absorption 6 months post-transplant.

*Methods: All pediatric (age < 18 years) liver transplants performed at our institution between 2012 and 2020 were retrospectively reviewed. Patients were excluded for multi-organ or re-transplant, non-FK-based immunosuppression, or patient death within 6 months of transplant. Immunosuppression includes FK506 and a corticosteroid taper, +/-mycophenolate. Target FK506 trough levels are 10 - 12 ng/mL for post-transplant months 0 - 3, and 8 - 10 ng/mL for months 3 - 6. FK506 absorption and oral bioavailability was assessed using Dose-Normalized Trough Concentration (DNTC), measured as the trough concentration (ng/mL) divided by the total daily dose (mg/kg/day) at 6 months post-transplant. Categorical variables presented as n (%) and continuous variables presented as mean (standard deviation). Association with DNTC was assessed using multivariable linear regression. Significant variable (p < 0.05) upon univariable linear regression were included in the multivariable model.

*Results: 88 pediatric liver transplant recipients met inclusion criteria (Table 1). Upon univariable linear regression, age, weight, diagnosis, total bilirubin, match MELD/PELD, biliary reconstruction technique, and graft type were significantly associated with 6-month FK506 DNTC. Upon multivariable linear regression, age, total bilirubin, match MELD/PELD > 25, and living donor liver graft remained significantly and independently associated with 6-month FK506 DNTC (Table 2). Total bilirubin, match MELD/PELD, and living donor graft were positively associated with DNTC, while age was negatively associated with DNTC.

*Conclusions: Novel pediatric characteristics at time of liver transplant associated with increased FK506 absorption 6-months post-transplant include younger age, living donor graft, MELD/PELD, and total bilirubin. These findings may help guide FK506 dosing and dose adjustments by identifying sub-groups of recipients with higher absorption and oral bioavailability.

« Back to 2022 American Transplant Congress