Methsuximide and Felbamate: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Felbamate
Methsuximide
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 concentrations of methsuximide active metabolites
Interaction Deep Dive
Concentrations of normethsuximide were increased after felbamate was added to therapy in 3 patients treated with methsuximide. The dose of methsuximide was decreased. The cause of the increase in normethsuximide concentrations is not known1.
Why it happens (mechanism)
Unknown
Common questions
Can I take Methsuximide and Felbamate together?
Increased concentrations of methsuximide active metabolites Always confirm with your pharmacist or prescriber before making any change.
How serious is the Methsuximide 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.
Questions for your pharmacist
- Does my dose of Methsuximide 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)
- Glue P, Banfield CR, Perhach JL, et al: Pharmacokinetic interactions with felbamate in vitro-in vivo correlation. Clin Pharmacokinet 1997; 33:214-224. PubMed
Keep reading about Felbamate
Keep reading about Methsuximide
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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