Quinidine and Ketoconazole Topical: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Ketoconazole Topical
Quinidine
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.
What happens
Increased quiNIDine exposure, increased risk of serious cardiovascular events and an increased risk of QT interval prolongation
Interaction Deep Dive
Concurrent use of ketoconazole and quiNIDine (class 1A antiarrhythmic with a narrow therapeutic index) is contraindicated, as this may result in increased quiNIDine exposure, increased risk of QT interval or QTc prolongation, and risk of torsades de pointes. Under no circumstances quiNIDine be coadministered with ketoconazole tablets, and up to one week after discontinuation of treatment with ketoconazole1. QuiNIDine levels rise when ketoconazole is coadministered 2. A single case report describes the association of ketoconazole with increased quiNIDine exposure, but no symptoms of quiNIDine toxicity were observed 3.
Why it happens (mechanism)
Additive QT interval prolongation; inhibition of CYP3A4-mediated metabolism of quiNIDine; additive QT interval prolongation
Literature reports
1 report — tap to read
a) Concomitant administration of ketoconazole 200 mg daily and quiNIDine 300 mg 4 times daily resulted in increased quiNIDine exposure from 2.7 mg/L to 6.9 mg/L in a 77-year-old man with leukemia who was being treated for chronic atrial fibrillation and candidal esophagitis. No symptoms related to quiNIDine toxicity were observed, and no new irregularities in heart rhythm were noted. It is suggested that ketoconazole may inhibit quiNIDine metabolism, and that close monitoring of quiNIDine plasma levels be undertaken in quiNIDine-treated patients when ketoconazole is added to the regimen 3.
Common questions
Can I take Quinidine and Ketoconazole Topical together?
Increased quiNIDine exposure, increased risk of serious cardiovascular events and an increased risk of QT interval prolongation Always confirm with your pharmacist or prescriber before making any change.
How serious is the Quinidine and Ketoconazole Topical 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.
Questions for your pharmacist
- Does my dose of Quinidine or Ketoconazole Topical 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)
- Product Information: Ketoconazole oral tablet, ketoconazole oral tablet. Taro Pharmaceuticals U.S.A. Inc. (per DailyMed), Hawthorne, NY, 2024. DailyMed
- Product Information: Quinaglute(R), quinidine gluconate. Berlex Laboratories, Wayne, NJ, 1999. DailyMed
- McNulty RM, Lazor JA, & Sketch M: Transient increase in plasma quinidine concentrations during ketoconazole-quinidine therapy. Clin Pharm 1989; 8:222-225.
Keep reading about Ketoconazole Topical
Keep reading about Quinidine
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