Erdafitinib and Phenytoin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Phenytoin
Erdafitinib
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
Reduced erdafitinib exposure
Interaction Deep Dive
Avoid coadministration of erdafitinib with a strong inducer of CYP3A4 as significant reduction in erdafitinib plasma concentrations and efficacy may result. Erdafitinib mean ratios for Cmax and AUC(inf) were 78% and 45%, respectively, when erdafitinib was coadministered with carBAMazepine (a strong CYP3A4 and weak CYP2C9 inducer) relative to erdafitinib alone1.
Why it happens (mechanism)
Induction of CYP3A4-mediated erdafitinib metabolism
Literature reports
1 report — tap to read
a) Erdafitinib mean ratios for Cmax and AUC(inf) were 78% and 45%, respectively, when erdafitinib was coadministered with carBAMazepine (a strong CYP3A4 and weak CYP2C9 inducer) relative to erdafitinib alone 1.
Common questions
Can I take Erdafitinib and Phenytoin together?
Reduced erdafitinib exposure Always confirm with your pharmacist or prescriber before making any change.
How serious is the Erdafitinib 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 Erdafitinib 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: BALVERSA(R) oral tablets, erdafitinib oral tablets. Janssen Products LP (per FDA), Horsham, PA, 2024. DailyMed
Keep reading about Phenytoin
Keep reading about Erdafitinib
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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