The impact of initiating posaconazole on tacrolimus pharmacokinetics in allogeneic stem cell transplantation

Background Posaconazole reduces the risk of invasive Aspergillus in transplant patients, but significantly inhibits tacrolimus metabolism. One study demonstrated that a three-fold dose reduction of tacrolimus was required to obtain therapeutic concentrations when used with posaconazole. However, with empiric dose reduction, there is a risk of subtherapeutic tacrolimus levels and subsequent graft failure or graft-versus-host disease. Overall, the existing data on the impact of posaconazole on tacrolimus pharmacokinetics is limited. Objective The purpose of this study is to determine whether tacrolimus doses should be decreased upon initiation of posaconazole in patients receiving an allogeneic stem cell transplant. Methods This is a retrospective chart review at an academic medical center. All allogeneic stem cell transplant adults who received concomitant posaconazole and tacrolimus from February 2016 through December 2017 were included. Results Seventy-nine patients identified using an internal electronic database were analyzed. The median time to therapeutic tacrolimus concentration was significantly longer in patients who did not receive an empiric dose reduction (0% DR, 10d; 1-30% DR, 4d; 31-65% DR, 5d; >65% DR, 4d; p = 0.0395). The rate of supratherapeutic levels was highest amongst patients who did not receive an empiric DR, and was noted to be significant compared to the group that had 31-65% DR (p < 0.001). Conclusion This study validates our current practice of instituting an empiric 50% dose reduction of oral tacrolimus to 0.03 mg/kg/day when used concomitantly with posaconazole to achieve therapeutic levels in allogeneic stem cell transplant patients.