Severe Neuropathic Pain With Concomitant Administration of Vincristine and Posaconazole.

Vincristine is a chemotherapeutic agent with a potential toxicity of sensorimotor peripheral neuropathy. Patients receiving chemotherapy are in an immunocompromised state and may require antifungal agents. Triazole antifungals are known inhibitors of cytochrome P450 (CYP) enzymes. Vincristine is a known CYP3A4 and CYP3A5 substrate, and concomitant administration with fluconazole or voriconazole has been reported to increase vincristine toxicity and peripheral neuropathy, but there is limited literature on posaconazole in this regard. This 5-year-old girl with pre-B-cell acute lymphoblastic leukemia received vincristine while receiving posaconazole for a mucormycosis infection and developed unexpectedly severe peripheral neuropathy. After recovery, the child continued on mucormycosis prophylaxis with posaconazole with instructions to hold for 2 days before and on the day of vincristine administration. This case illustrates the potentiating effect that posaconazole had on vincristine-associated neurotoxicity, and our approach to mitigating that negative interaction.