Dosing algorithm for concomitant administration of sirolimus, tacrolimus, and an azole after allogeneic hematopoietic stem cell transplantation.

Background: Allogeneic hematopoietic stem cell transplant patients are at risk of invasive fungal infections and prophylaxis with azole agents is common practice. The concomitant use of these agents with sirolimus and tacrolimus for the prevention of graft-versus-host disease may result in excessive immunosuppression or toxicity.

Methods: This retrospective study identified hospitalized patients who underwent allogeneic hematopoietic stem cell transplantation between August 2009 and April 2011 at Rush University Medical Center. From this group, patients who underwent concomitant tacrolimus, sirolimus, and azole therapy were included for evaluation. The immunosuppression dosing in conjunction with azole use at discharge was analyzed to develop a dosing algorithm dependent on whether fluconazole, posaconazole, or voriconazole was used.

Results: A total of 36 patients were screened for inclusion, of which 8 were excluded due to acute renal failure and/or hemolysis. The remaining patients were stratified by the azole they were concomitantly taking with tacrolimus and sirolimus. The fluconazole arm required the lowest magnitude of dose reductions, while voriconazole required the greatest.

Conclusion: Dose reductions of 50-75% for both sirolimus and tacrolimus, in combination with standard dosing of azole antifungal agents, were necessary to achieve therapeutic drug concentrations for immunosuppressants and potentially avoid toxicities.