Metronidazole with Carbamazepine Interaction Details

Brand Names Associated with Metronidazole

Brand Names Associated with Carbamazepine

Medical Content Editor Dr. Brian Staiger, PharmD
Last updated Jan 04, 2024

Interaction Effect

Increased carbamazepine serum concentrations and potential carbamazepine toxicity

Interaction Summary

Significantly increased carbamazepine serum concentrations and CNS toxicity have been reported in a patient receiving concurrent metronidazole. 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.

Severity

Moderate

Onset

Delayed

Evidence

Probable

How To Manage Interaction

When metronidazole and carbamazepine are coadministered, monitor carbamazepine serum concentrations and observe patients for signs and symptoms of carbamazepine toxicity (nausea, dizziness, diplopia, CNS effects). Doses of carbamazepine may need to be adjusted when metronidazole is added to or withdrawn from therapy.

Mechanism Of Interaction

Unknown but may involve inhibition of carbamazepine metabolism by metronidazole

Literature Reports

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 Cefazolin was added and trimethoprim/sulfamethoxazole withdrawn.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 .

Metronidazole Overview

• Metronidazole capsules and tablets are used to treat infections of the reproductive system, gastrointestinal (GI) tract, skin, heart, bone, joint, lung, blood, nervous system, and other areas of the body. Metronidazole capsules and tablets are also used to treat sexually transmitted diseases (STDs). Metronidazole extended-release (long-acting) tablets are used to treat bacterial vaginosis (an infection caused by too much of certain types of harmful bacteria in the vagina) in women. Metronidazole is in a class of medications called nitroimidazole antimicrobials. It works by stopping the growth of bacteria.

• Antibiotics will not work for colds, flu, or other viral infections. Using antibiotics when they are not needed increases your risk of getting an infection later that resists antibiotic treatment.

Carbamazepine Overview

• Carbamazepine is used alone or in combination with other medications to control certain types of seizures in people with epilepsy. It is also used to treat trigeminal neuralgia (a condition that causes facial nerve pain). Carbamazepine extended-release capsules (Equetro brand only) are also used to treat episodes of mania (frenzied, abnormally excited or irritated mood) or mixed episodes (symptoms of mania and depression that happen at the same time) in patients with bipolar I disorder (manic-depressive disorder; a disease that causes episodes of depression, episodes of mania, and other abnormal moods). Carbamazepine is in a class of medications called anticonvulsants. It works by reducing abnormal electrical activity in the brain.

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Definitions

Severity Categories

Contraindicated

These drugs, generally, should not be used together simultaneously due to the high risk of severe adverse effects. Combining these medications can lead to dangerous health outcomes and should be strictly avoided unless otherwise instructed by your provider.

Major

This interaction could result in very serious and potentially life-threatening consequences. If you are taking this drug combination, it is very important to be under close medical supervision to minimize severe side effects and ensure your safety. It may be necessary to change a medication or dosage to prevent harm.

Moderate

This interaction has the potential to worsen your medical condition or alter the effectiveness of your treatment. It's important that you are monitored closely and you potentially may need to make adjustments in your treatment plan or drug dosage to maintain optimal health.

Minor

While this interaction is unlikely to cause significant problems, it could intensify side effects or reduce the effectiveness of one or both medications. Monitoring for changes in symptoms and your condition is recommended, and adjustments may be made if needed to manage any increased or more pronounced side effects.

Onset

Rapid: Onset of drug interaction typically occurs within 24 hours of co-administration.

Delayed: Onset of drug interaction typically occurs more than 24 hours after co-administration.

Evidence

Level of documentation of the interaction.

Established: The interaction is documented and substantiated in peer-reviewed medical literature.

Theoretical: This interaction is not fully supported by current medical evidence or well-documented sources, but it is based on known drug mechanisms, drug effects, and other relevant information.

How To Manage The Interaction

Provides a detailed discussion on how patients and clinicians can approach the identified drug interaction as well as offers guidance on what to expect and strategies to potentially mitigate the effects of the interaction. This may include recommendations on adjusting medication dosages, altering the timing of drug administration, or closely monitoring for specific symptoms.

It's important to note that all medical situations are unique, and management approaches should be tailored to individual circumstances. Patients should always consult their healthcare provider for personalized advice and guidance on managing drug interactions effectively.

Mechanism Of Interaction

The theorized or clinically determined reason (i.e., mechanism) why the drug-drug interaction occurs.

Disclaimer: The information provided on this page is for informational purposes only and should not be considered medical advice. Always consult with a qualified healthcare professional regarding your specific circumstances and medical conditions.

Where Does Our Information Come From?

Information for our drug interactions is compiled from several drug compendia, including:

• Gold Standard Drug Database
• Micromedex
• Lexicomp
• DrugBank

The prescribing information for each drug, as published on DailyMED, is also used. 

Individual drug-drug interaction detail pages contain references specific to that interaction. You can click on the reference number within brackets '[]' to see what reference was utilized.

The information posted is fact-checked by HelloPharmacist clinicians and reviewed quarterly.