Drug interactions
Clarithromycin + Ondansetron
Severity: Major
Clarithromycin and Ondansetron: major interaction.
Last updated Sources: UK SmPC
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 prolong the QT interval, and clarithromycin may also raise ondansetron concentrations. Together this increases the risk of torsades de pointes.
What this interaction means in plain words
Clarithromycin and Ondansetron can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Clarithromycin belongs to Anti Bacterial; Ondansetron belongs to Gastrointestinal Tract.
Why it happens
Additive QT prolongation, with CYP3A4 inhibition by clarithromycin reducing ondansetron clearance.
What to do
Use an alternative antibiotic or antiemetic when feasible. If combined, obtain an ECG, correct electrolytes and use the lowest effective ondansetron dose.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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References
- Ondansetron 4 mg film-coated tablets - SmPC sections 4.3/4.5 (class statement: antibiotics; "antibiotics (such as erythromycin)") — electronic medicines compendium (UK SmPC)
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 Clarithromycin
- Astemizole + Clarithromycin Contraindicated
- Avanafil + Clarithromycin Contraindicated
- Cisapride + Clarithromycin Contraindicated
- Clarithromycin + Colchicine Contraindicated
- Clarithromycin + Conivaptan Contraindicated
- Clarithromycin + Dihydroergotamine Contraindicated
Frequently asked questions
Can I take Clarithromycin with Ondansetron?
MediHelp rates the interaction as major. Clarithromycin and Ondansetron can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Both drugs prolong the QT interval, and clarithromycin may also raise ondansetron concentrations. Together this increases the risk of torsades de pointes.
How serious is the interaction between Clarithromycin and Ondansetron?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Use an alternative antibiotic or antiemetic when feasible. If combined, obtain an ECG, correct electrolytes and use the lowest effective ondansetron dose.
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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