Voriconazole Autoinduction and Saturable Metabolism After Cessation of Rifampin in a Patient With Invasive Central Nervous System Aspergillus: Importance of Therapeutic Drug Monitoring.

PURPOSE: Optimization of antifungal therapy with voriconazole can be challenging due to inter- and intrapatient variability in voriconazole pharmacokinetics (PK). In this case, we introduce challenges in voriconazole therapy due to drug-drug interactions, autoinduction, and saturable metabolism.

SUMMARY: A 32-year-old male on chronic prednisone developed central nervous system (CNS) aspergillosis. He was started on high-dose intravenous (IV) voriconazole 8.5 mg/kg every 12 hours due to concerns for lasting induction effects of recent rifampin therapy. The initial voriconazole trough was 2 μg/mL. Frequent dose adjustments were made to maintain the therapeutic trough goal. On day 24 of voriconazole therapy, his trough was undetectable on IV voriconazole 5.5 mg/kg every 12 hours. His dose was escalated to 8.5 mg/kg every 12 hours to avoid subtherapeutic levels and therapeutic failure. On day 48, his trough level was 1.1 μg/mL on the same dose. His regimen was changed to 6.5 mg/kg every 8 hours at this point. Sixteen days after this regimen on day 74 of voriconazole therapy, his trough was 27.2 μg/mL indicating saturable PK of voriconazole in the absence of interacting drugs.

CONCLUSION: Our findings highlight the unpredictable PK of voriconazole and reinforce the importance of continuous therapeutic drug monitoring in critically ill patients.