Metronidazole and Carbamazepine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Carbamazepine
Metronidazole
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 carbamazepine serum concentrations and potential carbamazepine toxicity
Interaction Deep Dive
Significantly increased carbamazepine serum concentrations and CNS toxicity have been reported in a patient receiving concurrent metronidazole1. The mechanism was thought to be inhibition by metronidazole of cytochrome P450 aromatic oxidative metabolism of carbamazepine. Further study is needed to validate this interaction.
Why it happens (mechanism)
Unknown but may involve inhibition of carbamazepine metabolism by metronidazole
Literature reports
1 report — tap to read
a) A 49-year-old woman was seen in the ER with left quadrant pain thought to be caused by diverticulitis. She was using carbamazepine 1000 mg daily for bipolar disorder. Her other medications included conjugated estrogens and alprazolam. Her carbamazepine serum concentration at 12 hours was 9 mcg/mL (38 mcmol/L). She was then started on metronidazole 250 mg three times a day and trimethoprim/sulfamethoxazole double strength twice a day. Two days later she was admitted for worsening symptoms. Her metronidazole was increased to 500 mg intravenously every eight hours. Cefazolin was added and trimethoprim/sulfamethoxazole withdrawn. Two days later she reported nausea, dizziness, and diplopia. At that time, her 10-hour carbamazepine serum concentration was 14.3 mcg/mL (60.5 mcmol/L), a 60% increase over the previous 9 mcg/mL (38 mcmol/L). The mechanism of this interaction was thought to be inhibition of the hepatic cytochrome P450 enzyme system by metronidazole 1.
Common questions
Can I take Metronidazole and Carbamazepine together?
Increased carbamazepine serum concentrations and potential carbamazepine toxicity Always confirm with your pharmacist or prescriber before making any change.
How serious is the Metronidazole 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 "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 Metronidazole 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 (1)
- Patterson BD: Possible interaction between metronidazole and carbamazepine (letter). Ann Pharmacother 1994; 28:1303-1304. PubMed
Keep reading about Carbamazepine
Keep reading about Metronidazole
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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