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Purpose: In July 2010, an initial tacrolimus dosing protocol was implemented in the heart transplant population at our institution. The objective of this study was to compare the incidence of supratherapeutic tacrolimus troughs before and after the introduction of the initial tacrolimus dosing protocol and corresponding outcomes of acute kidney injury and early acute graft rejection.
Methods: This retrospective study included 133 patients who underwent orthotopic heart transplantation between July 1, 2008 and July 31, 2011. Patients were excluded from this study if they received multi-organ transplantation, had undergone a previous organ transplant, received intravenous tacrolimus, were less than 18 years of age, or did not have tacrolimus trough levels reported. Acute kidney injury was evaluated using modified RIFLE criteria. Rejection was defined as a biopsy grade greater than 1R using the International Society for Heart and Lung Transplantation (ISHLT) standardized cardiac biopsy grading criteria.
Results: Implementation of an initial dosing protocol resulted in a significant decrease in the incidence of supratherapeutic tacrolimus trough levels in post-protocol patients (59.8% vs 35.3%, p=0.008). Fewer patients in the post-protocol group developed acute kidney injury during post-transplant week one (56.1% vs 39.2%, p=0.07) and post-transplant week two (34.1% vs 19.6%, p=0.08). Post-protocol patients took longer to achieve therapeutic tacrolimus trough levels (8±3 vs 5±3 days, p<0.01). There was no significant difference in the incidence of early acute graft rejection between groups (6.1% vs 2.0%, p=0.7).
Conclusions: Implementation of an initial tacrolimus dosing protocol was associated with a significant reduction in the incidence of supratherapeutic tacrolimus trough levels. A corresponding reduction in the incidence of acute kidney injury was likely the result of a less aggressive initial dosing approach. No difference was seen in rates of early acute graft rejection, and this initial dosing protocol remains the standard practice at the institution.