Drug interactions
Metronidazole + Ondansetron
Severity: Moderate
Metronidazole and Ondansetron: 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 have been associated with QT prolongation, so combining them may increase the risk of arrhythmia, especially with intravenous ondansetron at higher doses. The risk is greatest with hypokalemia, hypomagnesemia, or underlying heart disease.
What this interaction means in plain words
Metronidazole and Ondansetron 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.
Metronidazole belongs to Anti Parasitic; Ondansetron belongs to Gastrointestinal Tract.
Why it happens
Additive effects on cardiac repolarization leading to QTc prolongation.
What to do
Correct potassium and magnesium, keep intravenous ondansetron doses low, and obtain an ECG in patients with other QT risk factors.
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 Ondansetron
- Apomorphine + Ondansetron Contraindicated
- Ondansetron + Thioridazine Contraindicated
- Ondansetron + Vandetanib Contraindicated
- Adagrasib + Ondansetron Major
- Amiodarone + Ondansetron Major
- Amisulpride + Ondansetron Major
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 Metronidazole with Ondansetron?
MediHelp rates the interaction as moderate. Metronidazole and Ondansetron 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 have been associated with QT prolongation, so combining them may increase the risk of arrhythmia, especially with intravenous ondansetron at higher doses. The risk is greatest with hypokalemia, hypomagnesemia, or underlying heart disease.
How serious is the interaction between Metronidazole and Ondansetron?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Correct potassium and magnesium, keep intravenous ondansetron doses low, and obtain an ECG in patients with other QT risk factors.
What other medicines interact with Ondansetron?
MediHelp also lists interactions of Ondansetron with, for example, Apomorphine, Thioridazine, Vandetanib. The full list is on the Ondansetron page.
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