Drug interactions
Isoniazid + Metronidazole
Severity: Moderate
Isoniazid and Metronidazole: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Both drugs can cause peripheral neuropathy and neuropsychiatric effects such as confusion, psychosis or seizures. Used together, particularly in patients with other risk factors, these toxicities may be additive.
What this interaction means in plain words
Isoniazid and Metronidazole can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Isoniazid belongs to Anti Bacterial; Metronidazole belongs to Anti Parasitic.
Why it happens
Additive neurotoxicity; isoniazid interferes with pyridoxine metabolism and metronidazole has direct neurotoxic potential.
What to do
Monitor for new paresthesias, mood or behavioral change and give pyridoxine supplementation with isoniazid. Stop or replace metronidazole if neurotoxic symptoms emerge.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Isoniazid
Other interactions of Metronidazole
- Ethanol + Metronidazole Contraindicated
- Metronidazole + Pimozide Contraindicated
- Amiodarone + Metronidazole Major
- Disulfiram + Metronidazole Major
- Ergotamine + Metronidazole Major
- Lomitapide + Metronidazole Major
Frequently asked questions
Can I take Isoniazid with Metronidazole?
MediHelp rates the interaction as moderate. Isoniazid and Metronidazole can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Both drugs can cause peripheral neuropathy and neuropsychiatric effects such as confusion, psychosis or seizures. Used together, particularly in patients with other risk factors, these toxicities may be additive.
How serious is the interaction between Isoniazid and Metronidazole?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor for new paresthesias, mood or behavioral change and give pyridoxine supplementation with isoniazid. Stop or replace metronidazole if neurotoxic symptoms emerge.
What other medicines interact with Isoniazid?
MediHelp also lists interactions of Isoniazid with, for example, Bacillus calmette-guerin substrain tice, Benzhydrocodone / acetaminophen, Carbamazepine. The full list is on the Isoniazid page.
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