Phenytoin and Miconazole: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Phenytoin
Miconazole
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Increased phenytoin or fosphenytoin (prodrug of phenytoin) exposure and an increased risk of phenytoin or fosphenytoin toxicity (ataxia, hyperreflexia, nystagmus, tremor)
Interaction Deep Dive
Use caution with coadministration of miconazole and phenytoin or fosphenytoin (prodrug of phenytoin), as concurrent use may lead to increased exposure of phenytoin or fosphenytoin and an increased risk of adverse effects1. Consider phenytoin or fosphenytoin dose adjustments when miconazole is added to or withdrawn from a patient's regimen 12. In a case report of a patient stabilized on phenytoin, the phenytoin levels increased when miconazole and flucytosine were added to the therapy. The increase in the phenytoin level was attributed to the addition of miconazole 5. Monitor patients for signs of phenytoin or fosphenytoin toxicity (ataxia, hyperreflexia, nystagmus, tremor) when receiving miconazole concurrently 4.
Why it happens (mechanism)
Inhibition of CYP2C9-mediated metabolism of phenytoin
Literature reports
1 report — tap to read
a) In a case report of a patient stabilized on phenytoin, the phenytoin levels increased when miconazole and flucytosine were added to the therapy. The increase in the phenytoin level was attributed to the addition of miconazole 5.
Common questions
Can I take Phenytoin and Miconazole together?
Increased phenytoin or fosphenytoin (prodrug of phenytoin) exposure and an increased risk of phenytoin or fosphenytoin toxicity (ataxia, hyperreflexia, nystagmus, tremor) Always confirm with your pharmacist or prescriber before making any change.
How serious is the Phenytoin and Miconazole interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
Questions for your pharmacist
- Does my dose of Phenytoin or Miconazole need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (5)
- Product Information: Dilantin-125(R) oral suspension, phenytoin oral suspension. Parke-Davis (per FDA), New York, NY, 2014. DailyMed
- Product Information: FOSPHENYTOIN SODIUM intravenous and intramuscular injection, fosphenytoin sodium intravenous and intramuscular injection. SAGENT Pharmaceuticals (per Dailymed), Schaumburg, IL, 2024. DailyMed
- Product Information: PHENYTOIN SODIUM intravenous and intramuscular injection, phenytoin sodium intravenous and intramuscular injection. Acella Pharmaceuticals, LLC (per Dailymed), Alpharetta, GA, 2024. DailyMed
- Product Information: PHENYTOIN SODIUM oral extended-release capsules, phenytoin sodium oral extended-release capsules. Sun Pharmaceutical Industries, Inc. (per Dailymed), Cranbury, NJ, 2023. DailyMed
- Rolan PE, Somogyi AA, Drew MJ, et al: Phenytoin intoxication during treatment with parenteral miconazole. Br Med J 1983; 287:1760. PubMed
Keep reading about Phenytoin
Keep reading about Miconazole
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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