Warfarin and Felbamate: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Warfarin
Felbamate
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
An increased risk of bleeding
Interaction Deep Dive
One case has been reported in which concurrent use of felbamate in a patient stabilized on warfarin resulted in a significant rise in international normalized ratio (INR) (from an average range of 2.5 to 3.5 to a peak of 18.2)1. Anticoagulation in the INR range of 2.5 to 3.5 was reestablished at about half the warfarin dose taken previously.
Why it happens (mechanism)
Decreased warfarin metabolism
Common questions
Can I take Warfarin and Felbamate together?
An increased risk of bleeding Always confirm with your pharmacist or prescriber before making any change.
How serious is the Warfarin and Felbamate interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Warfarin or Felbamate 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 anything you'd monitor while I'm on both?
References (1)
- Tisdel KA, Israel DS, & Kolb KW: Warfarin-felbamate interaction: first report. Ann Pharmacother 1994; 28:805. PubMed
Keep reading about Warfarin
Keep reading about Felbamate
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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