Drug Interaction Report

Ketoconazole Topical and Cimetidine: Interaction Details

A pharmacist-reviewed analysis of the Ketoconazole Topical and Cimetidine 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

Cimetidine

Tagamet
+

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
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 546 documented Ketoconazole Topical interactions, 380 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
delayed
Evidence
probable
Severity
Major

What happens

Reduced ketoconazole exposure and reduced efficacy of ketoconazole

Interaction Deep Dive

Caution is advised when using cimetidine together with ketoconazole, as coadministration may reduce ketoconazole exposure leading to a loss of ketoconazole therapeutic effect. If concomitant use is required, administer ketoconazole with an acidic beverage such as non-diet cola and monitor antifungal activity closely. An increase in ketoconazole dosage may be necessary1. Clinical studies demonstrated that concurrent administration of ketoconazole with cimetidine significantly decreased the AUC of ketoconazole 23.

Why it happens (mechanism)

Changes in gastric pH; reduced ketoconazole absorption

Literature reports

1 report — tap to read

a) The area under the plasma concentration-time curve for ketoconazole was reduced by 65% when administered two hours after cimetidine therapy. In the same study, concomitant administration of ketoconazole in an acid solution two hours after cimetidine therapy increased absorption by 52% 23.

Common questions

Can I take Ketoconazole Topical and Cimetidine together?

Reduced ketoconazole exposure and reduced efficacy of ketoconazole Always confirm with your pharmacist or prescriber before making any change.

How serious is the Ketoconazole Topical and Cimetidine interaction?

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

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.

Questions for your pharmacist

  • Does my dose of Ketoconazole Topical or Cimetidine 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: Ketoconazole oral tablet, ketoconazole oral tablet. Taro Pharmaceuticals U.S.A. Inc. (per DailyMed), Hawthorne, NY, 2024. DailyMed
  2. Blum RA, D'Andrea DT, Florentino BM, et al: Increased gastric pH and the bioavailability of fluconazole and ketoconazole. Ann Intern Med 1991; 114:755-757. PubMed
  3. Van der Meer JWM, Keuning JJ, Scheijgrond HW, et al: The influence of gastric acidity on the bioavailability of ketoconazole. J Antimicrob Chemother 1980; 6:552-554.
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Cimetidine

Keep reading about Cimetidine

All Cimetidine interactions (83)
Also serious with: Dofetilide Colchicine Octreotide Injection Meloxicam Injection
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:

Cimetidine + Activated Charcoal Pu-erh Tea St. John's Wort Adrafinil African Wild Potato Banderol Beer Bitter Melon + 87 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.