Ethosuximide and Carbamazepine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Carbamazepine
Ethosuximide
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 succinimide (ethosuximide, phensuximide) exposure and potential loss of efficacy
Interaction Deep Dive
Concomitant use of carBAMazepine (a CYP3A4 inducer) and succinimides (CYP3A4 substrates) may cause decreased succinimide levels (ethosuximide, phensuximide). It may be necessary to monitor the concentrations of succinimides and adjust the dosage23. Two studies have documented that ethosuximide levels are altered during carBAMazepine therapy, including decreased steady-state plasma concentrations, decreased half-life, and increased clearance 14.
Why it happens (mechanism)
Induction of CYP3A4-mediated succinimide metabolism by carBAMazepine
Literature reports
2 reports — tap to read
a) In a study of 22 volunteers, the effects of chronic epileptic medication on the pharmacokinetics of ethosuximide were evaluated. The study consisted of 10 epileptic patients undergoing chronic treatment with carBAMazepine, phenytoin, or PHENobarbital, and 12 healthy control subjects taking no chronic medications. Each subject received a single 500 mg oral dose of ethosuximide after an overnight fast. Patients on chronic epileptic therapy had a decreased mean ethosuximide half-life of 29 hours compared to 53.7 hours for control subjects. Patients on chronic epileptic therapy also had higher oral clearance values and slightly decreased apparent volume of distribution values compared to control patients 1.
b) Ethosuximide levels were shown to be altered by carBAMazepine therapy. Concomitant therapy with carBAMazepine 200 mg daily and ethosuximide 250 mg twice daily resulted in a lowering of ethosuximide steady-state plasma concentrations. The clearance of ethosuximide was shown to increase with a concomitant decrease in serum half-life 4.
Common questions
Can I take Ethosuximide and Carbamazepine together?
Reduced succinimide (ethosuximide, phensuximide) exposure and potential loss of efficacy Always confirm with your pharmacist or prescriber before making any change.
How serious is the Ethosuximide and Carbamazepine 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 "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Ethosuximide or Carbamazepine 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 (4)
- Giaccone M, Bartoli A, Gatti G, et al: Effect of enzyme inducing anticonvulsants on ethosuximide pharmacokinetics in epileptic patients. Br J Clin Pharmacol 1996; 41:575-579. DOI
- Product Information: Tegretol(R)-XR oral extended-release tablets, carbamazepine oral extended-release tablets. Novartis Pharmaceuticals Corporation (per FDA), East Hanover, NJ, 2023. DailyMed
- Product Information: Tegretol(R) oral chewable tablets, oral tablets, oral suspension, carbamazepine oral chewable tablets, oral tablets, oral suspension. Novartis Pharmaceuticals Corporation (per FDA), East Hanover, NJ, 2023. DailyMed
- Warren JW, Benmaman JD, Wannamaker BB, et al: Kinetics of a carbamazepine-ethosuximide interaction. Clin Pharmacol Ther 1980; 28:646-650. PubMed
Keep reading about Carbamazepine
Keep reading about Ethosuximide
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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