Drug Interaction Report

Ketoconazole Topical and Erythromycin: Interaction Details

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

AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Erythromycin

Erythrocin Stearate
+

Ketoconazole Topical

Extina® Foam Ketozole® Cream Kuric Nizoral AD® Shampoo Nizoral® Cream Nizoral® Shampoo Xolegel®
Dr. Brian Staiger, PharmD, BCPS
Medically reviewed by
Dr. Brian Staiger, PharmD, BCPS
Updated Aug 8, 2026
Editorial policy · Data sources
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Interaction severity
Contraindicated
These should generally not be used together.
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 546 documented Ketoconazole Topical interactions, 127 are rated contraindicated — 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
delayed
Evidence
probable
Severity
Contraindicated

What happens

Increased erythromycin exposure, an increased ketoconazole exposure and an increased risk of QT interval prolongation

Interaction Deep Dive

Coadministration of ketoconazole (a strong CYP3A4 inhibitor that may prolong the QT interval) with CYP3A4 substrates that are known to prolong the QT interval, such as erythromycin is contraindicated as it may cause increased CYP3A4 substrates exposure, increasing the risk for QT interval prolongation and result in life-threatening ventricular tachyarrhythmias such as torsade de pointes1. Similar inhibition of erythromycin metabolism (a CYP3A4 substrate) is expected with concurrent therapy involving ketoconazole, a CYP3A4 inhibitor 2.

Why it happens (mechanism)

Inhibition of CYP3A4-mediated metabolism of erythromycin; inhibition of CYP3A4-mediated metabolism of ketoconazole; additive QT interval prolongation

Common questions

Can I take Ketoconazole Topical and Erythromycin together?

Increased erythromycin exposure, an increased ketoconazole exposure and an increased risk of QT interval prolongation Always confirm with your pharmacist or prescriber before making any change.

How serious is the Ketoconazole Topical and Erythromycin interaction?

It is rated contraindicated. These should generally not be used together.

How quickly could this interaction happen?

The documented onset is "delayed". Effects tend to build up gradually over days to weeks.

How strong is the evidence for this interaction?

The evidence is graded "probable". Good supporting evidence, though not definitively proven.

From our Q&A

Real reader questions about these medications, each personally answered by our pharmacist:

Questions for your pharmacist

  • Does my dose of Ketoconazole Topical or Erythromycin 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 (2)

  1. Product Information: Ketoconazole oral tablet, ketoconazole oral tablet. Taro Pharmaceuticals U.S.A. Inc. (per DailyMed), Hawthorne, NY, 2024. DailyMed
  2. Ray WA, Murray KT, Meredith S, et al: Oral erythromycin and the risk of sudden death from cardiac causes. N Engl J Med 2004; 351(11):1089-1096. DOI
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Erythromycin

Keep reading about Erythromycin

All Erythromycin interactions (186)
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Ketoconazole Topical

Keep reading about Ketoconazole Topical

All Ketoconazole Topical interactions (546) Ketoconazole Topical drug information
Also serious with: Colchicine Conivaptan Crizotinib Dabrafenib
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:

Erythromycin + Activated Charcoal American Hellebore Arsenic Beer Cesium Ephedra Grapefruit Oleander + 196 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.