Voriconazole and Phenytoin Interaction

Understanding the Voriconazole and Phenytoin Interaction

FDA-approved prescribing information for these two drugs flags their combination as a major-severity interaction. Voriconazole belongs to the Azole Antifungal class and Phenytoin belongs to the Anticonvulsant (Hydantoin) class - two categories that can collide when co-prescribed. The mechanism described in FDA labeling is: Phenytoin speeds up how fast the body gets rid of voriconazole, while voriconazole slows down the breakdown of phenytoin. Severity tiers matter: major flags generally advise avoidance, moderate flags often require monitoring or dose adjustment, and minor flags may only call for awareness.

Context around a specific patient determines real-world impact. Voriconazole has 50 total documented interactions on file in this dataset, and Phenytoin has 147. Each additional medication compounds the interaction surface, which is why pharmacists run full-profile checks rather than evaluating one pair at a time. FDA-derived guidance for this pair is: Your doctor will need to increase your voriconazole dose and monitor your phenytoin blood levels very closely. Timing of doses, renal and hepatic function, age, and other concurrent prescriptions all shape whether a labeled interaction matters clinically.

An interaction flag is not a verdict. A large share of labeled interactions are managed routinely in clinical practice, the fix may be as simple as spacing doses or adding a monitoring test. Others require the prescriber to choose a different medication entirely. This page surfaces FDA-sourced labeling and openFDA data for educational purposes only; it is not medical advice and cannot account for your full clinical picture. Never start, stop, or adjust either Voriconazole or Phenytoin based on a web page, speak with your prescriber or pharmacist before making any change.