Voriconazole/Phenytoin Interactions

This information is generalized and not intended as specific medical advice. Consult your healthcare professional before taking or discontinuing any drug or commencing any course of treatment.

Medical warning:

Serious. These medicines may interact and cause very harmful effects. Contact your healthcare professional (e.g. doctor or pharmacist) for more information.

How the interaction occurs:

Phenytoin may speed up how quickly your liver processes voriconazole. Voriconazole may slow down how quickly your liver processes phenytoin.

What might happen:

Your voriconazole may not work as well at treating your infection. The blood levels of your phenytoin may increase and cause toxic effects. You may experience slurred speech, increased confusion, nausea, unsteadiness walking, weakness, fatigue, or dizziness.

What you should do about this interaction:

Let your healthcare professionals (e.g. doctor or pharmacist) know that you are taking these medicines together. Your doctor may want to change your medicines. Let your doctor know if you experience slurred speech, increased confusion, nausea, unsteadiness walking, weakness, fatigue, dizziness, or trouble sleeping.Your healthcare professionals may already be aware of this interaction and may be monitoring you for it. Do not start, stop, or change the dosage of any medicine before checking with them first.

  • 1.Vfend (voriconazole) US prescribing information. Pfizer Inc. January, 2019.
  • 2.Dilantin (phenytoin sodium) US prescribing information. Pfizer, Inc. November, 2016.
  • 3.Dolton MJ, Mikus G, Weiss J, Ray JE, McLachlan AJ. Understanding variability with voriconazole using a population pharmacokinetic approach: implications for optimal dosing. J Antimicrob Chemother 2014 Jun; 69(6):1633-41.
  • 4.Purkins L, Wood N, Ghahramani P, Love ER, Eve MD, Fielding A. Coadministration of voriconazole and phenytoin: pharmacokinetic interaction, safety, and toleration. Br J Clin Pharmacol 2003 Dec;56 Suppl 1:37-44.

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CONDITIONS OF USE: The information in this database is intended to supplement, not substitute for, the expertise and judgment of healthcare professionals. The information is not intended to cover all possible uses, directions, precautions, drug interactions or adverse effects, nor should it be construed to indicate that use of a particular drug is safe, appropriate or effective for you or anyone else. A healthcare professional should be consulted before taking any drug, changing any diet or commencing or discontinuing any course of treatment.