Enasidenib and Phenytoin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Phenytoin
Enasidenib
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 CYP2C19 substrate exposure and an increased risk of CYP2C19 substrate-related adverse effects
Interaction Deep Dive
Avoid concomitant use of enasidenib (a CYP2C19 inhibitor) and a CYP2C19 substrate with NTI. Concomitant use increases the exposure of CYP2C19 substrate, where small concentration changes may lead to serious adverse reactions. In the drug interaction studies, omeprazole (a sensitive CYP2C19 substrate) AUC (o to inf) and Cmax increased by 86% and 47%, respectively, following concomitant use of multiple doses of enasidenib 100 mg with a single oral dose of omeprazole 40 mg1.
Why it happens (mechanism)
Inhibition of CYP2C19-substrate metabolism by enasidenib
Literature reports
1 report — tap to read
a) In the drug interaction studies, omeprazole (a sensitive CYP2C19 substrate) AUC (o to inf) and Cmax increased by 86% and 47%, respectively, following concomitant use of multiple doses of enasidenib 100 mg with a single oral dose of omeprazole 40 mg 1.
Common questions
Can I take Enasidenib and Phenytoin together?
Increased CYP2C19 substrate exposure and an increased risk of CYP2C19 substrate-related adverse effects Always confirm with your pharmacist or prescriber before making any change.
How serious is the Enasidenib and Phenytoin 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 Enasidenib or Phenytoin 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 (1)
- Product Information: IDHIFA(R) oral tablets, enasidenib oral tablets. Bristol-Myers Squibb (per FDA), Princeton, NJ, 2023. DailyMed
Keep reading about Phenytoin
Keep reading about Enasidenib
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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