*Purpose: Successful renal transplantation requires complex medication regimens that rely heavily on strict adherence to be effective. Variability in immunosuppression exposure, specifically tacrolimus, is associated with poor allograft outcomes. Wide intrapatient variability of tacrolimus trough concentrations (Vtac) is likely, in part, attributable to poor medication adherence. Once-daily tacrolimus formulations create opportunity to simplify therapeutic regimens, and this study aims to evaluate their impact on Vtac, and ultimately transplant outcomes.

*Methods: This retrospective cohort study investigated stable adolescent and young adult (AYA) renal transplant recipients converted from immediate-related tacrolimus (IR-Tac) to extended-release tacrolimus (ER-Tac). Subjects served as their own controls. Vtac was assessed prior to and at five time points post-conversion to ER-Tac over 36-month follow-up. Secondary outcome measures included graft function, infection rates, and effect on modifiable treatment-related factors.

*Results: Twenty-eight AYA subjects were converted from IR-Tac to ER-Tac. Vtac significantly improved following conversion and was sustained for 36 months (Vtac₀ 2.32 vs. Vtac₅ 0.83, p < 0.05). Renal function remained stable and biopsy proven acute rejection (BPAR) rates were modest (14%). Mean pill burden was reduced by 15% and 42.9% of subjects achieved a once-daily medication regimen.

*Conclusions: Conversion from IR-Tac to ER-Tac in this AYA population significantly improved Vtac with sustained effect over 3 years. This effect is likely attributable in part to simplification of the medication regimen and presumably improved medication adherence. Furthermore, such conversion does not appear to compromise graft function.

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