Management of Drug and Food Interactions with Azole Antifungal Agents in Transplant Recipients

Azole antifungal agents are frequently used in hematopoietic stem cell and solid organ transplant recipients for prevention or treatment of invasive fungal infections. However, because of metabolism by or substrate activity for various isoenzymes of the cytochrome P450 system and/or P‐glycoprotein, azole antifungals have the potential to interact with many of the drugs commonly used in these patient populations. Thus, to identify drug interactions that may result between azole antifungals and other drugs, we conducted a literature search of the MEDLINE database (1966‐December 2009) for English‐language articles on drug interaction studies involving the azole antifungal agents fluconazole, itraconazole, voriconazole, and posaconazole. Another literature search between each of the azoles and the immunosuppressants cyclosporine, tacrolimus, and sirolimus, as well as the corticosteroids methylprednisolone, dexamethasone, prednisolone, and prednisone, was also conducted. Concomitant administration of azoles and immunosuppressive agents may cause clinically significant drug interactions resulting in extreme immunosuppression or toxicity. The magnitude and duration of an interaction between azoles and immunosuppressants are not class effects of the azoles, but differ between drug combinations and are subject to interpatient variability. Drug interactions in the transplant recipient receiving azole therapy may also occur with antibiotics, chemotherapeutic agents, and acid‐suppressive therapies, among other drugs. Initiation of an azole antifungal in transplant recipients nearly ensures a drug‐drug interaction, but often these drugs are required. Management of these interactions first involves knowledge of the potential drug interaction, appropriate dosage adjustments when necessary, and therapeutic or clinical monitoring at an appropriate point in therapy to assess the drug‐drug interaction (e.g., immunosuppressive drug concentrations, signs and symptoms of toxicity). These aspects of drug interaction management are essential not only at the initiation of azole antifungal therapy, but also when these agents are removed from the regimen.