Prior Amiodarone Exposure Reduces Tacrolimus Dosing Requirements in Heart Transplant Recipients

Introduction: Amiodarone use prior to heart transplant is independently associated with a higher rate of severe primary graft dysfunction and in-hospital mortality. Amiodarone may also alter the pharmacokinetics of medications metabolized via cytochrome P450. No data exist regarding the interaction between pretransplant amiodarone and tacrolimus concentrations. Design: Single-center retrospective study of transplant patients between January 1, 2014, and June 30, 2016. A therapeutic tacrolimus concentration was defined as a trough level between 8 and 15 ng/mL for 2 consecutive days. The primary outcome was the tacrolimus therapeutic weight-based dosing requirements (mg/kg/day) for patients receiving amiodarone prior to transplant when compared to those without prior receipt of amiodarone. Secondary outcomes include the incidence of cellular rejection and mortality within 6 months posttransplant. Results: Multi-organ transplant recipients (n = 3), retransplants (n = 9), those who died prior to a therapeutic level (n = 1), and those receiving amiodarone posttransplant (n = 7) were excluded from the analysis. Of the 80 patients included, 34 (42%) received amiodarone prior to transplant. Patient characteristics were similar, with the exception of primary graft dysfunction incidence (38% in amiodarone vs 8.5% in control, P =.001). The median therapeutic dose was 0.1 (interquartile range [IQR]: 0.07-0.12) versus 0.13 (IQR: 0.09-0.17) in the amiodarone and control groups, respectively, (P <.01). No significant difference in mortality or rejection was noted. Conclusion: Patients receiving amiodarone prior to transplant require a lower weight-based dose of tacrolimus.