Drug Interaction Report

Azithromycin and Ondansetron: Interaction Details

A pharmacist-reviewed analysis of the Azithromycin and Ondansetron interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Jul 11, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Ondansetron

No brand names on record
+

Azithromycin

AzaSite Zithromax Zithromax® Zithromax® Single Dose Packets Zithromax® Tri-Paks® Zithromax® Z-Paks® Zmax®
Dr. Brian Staiger, PharmD, BCPS
Medically reviewed by
Dr. Brian Staiger, PharmD, BCPS
Updated Jul 11, 2026
Editorial policy · Data sources
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Interaction severity
Major
Potentially serious — often needs a change or close monitoring.
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.

Of 299 documented Azithromycin interactions, 264 are rated major — including this one.
Worried about symptoms right now? Contact your pharmacist or prescriber, or call Poison Control at 1-800-222-1222 (US). Call 911 for an emergency.
Onset
unspecified
Evidence
theoretical
Severity
Major

What happens

An increased risk of QT interval prolongation

Interaction Deep Dive

Both azithromycin and ondansetron have been associated with QT interval prolongation23. Due to the potential for additive effects on the QT interval, ECG monitoring is recommended if concurrent therapy is required 3 and also consider the risk of QT prolongation which can be fatal 1.

Why it happens (mechanism)

Additive QT interval prolongation

Common questions

Can I take Azithromycin and Ondansetron together?

An increased risk of QT interval prolongation Always confirm with your pharmacist or prescriber before making any change.

How serious is the Azithromycin and Ondansetron interaction?

It is rated major. Potentially serious — often needs a change or close monitoring.

How quickly could this interaction happen?

The documented onset is "unspecified". The timing of this interaction is not well characterized.

How strong is the evidence for this interaction?

The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.

Questions for your pharmacist

  • Does my dose of Azithromycin or Ondansetron 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 a safer alternative to one of these medications for me?

References (3)

  1. Product Information: ZMAX(R) oral extended-release suspension, azithromycin oral extended-release suspension. Pfizer Inc (per FDA), New York, NY, 2021. DailyMed
  2. Product Information: ZITHROMAX(R) intravenous injection, azithromycin intravenous injection. Pfizer Labs (per FDA), New York, NY, 2016. DailyMed
  3. Product Information: ZOFRAN ODT(R) oral disintegrating tablets, ondansetron oral disintegrating tablets. GlaxoSmithKline (per FDA), Research Triangle Park, NC, 2011. DailyMed
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Ondansetron

Keep reading about Ondansetron

All Ondansetron interactions (84)
Also serious with: Ketoconazole Topical Palonosetron Injection Capmatinib Morphine Injection
Azithromycin

Keep reading about Azithromycin

All Azithromycin interactions (299) Azithromycin drug information
Also serious with: Pimozide Mesoridazine Levoketoconazole Colchicine
Beyond drug–drug

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:

Ondansetron + Activated Charcoal Grapefruit Lithium St. John's Wort 1,3-dmaa 5-htp Acacia Rigidula Acetyl-l-carnitine + 187 more
Azithromycin + Activated Charcoal American Hellebore Arsenic Cesium Ephedra Grapefruit Oleander Sida Cordifolia + 84 more

major · moderate · minor — check everything you take with our drug–supplement interaction checker.

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This information is for education, not a substitute for professional medical advice. Do not start, stop, or change any medication without talking to your pharmacist or prescriber.