Futibatinib and Fosphenytoin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Fosphenytoin
Futibatinib
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 futibatinib exposure and reduced efficacy
Interaction Deep Dive
Avoid concomitant use of futibatinib (CYP3A substrate) with strong CYP3A inducers as it may reduce the exposure of futibatinib, which may reduce the efficacy of futibatinib. In a drug interaction study, coadministration of multiple doses of rifAMPin (a strong CYP3A inducer) decreased single-dose futibatinib Cmax by 53% and AUC by 64%1.
Why it happens (mechanism)
Induction of CYP3A-mediated metabolism of futibatinib
Literature reports
1 report — tap to read
a) In a drug interaction study, coadministration of multiple doses of rifAMPin (a strong CYP3A inducer) decreased single-dose futibatinib Cmax by 53% and AUC by 64% 1.
Common questions
Can I take Futibatinib and Fosphenytoin together?
Reduced futibatinib exposure and reduced efficacy Always confirm with your pharmacist or prescriber before making any change.
How serious is the Futibatinib and Fosphenytoin 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 "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
Questions for your pharmacist
- Does my dose of Futibatinib or Fosphenytoin 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: LYTGOBI® oral tablets, futibatinib oral tablets. Taiho Oncology Inc (per FDA), Princeton, NJ, 2025. DailyMed
Keep reading about Fosphenytoin
Keep reading about Futibatinib
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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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