Toremifene 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
Toremifene
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 toremifene exposure and an increased risk of QT interval prolongation, ventricular tachycardia or torsade de pointes
Interaction Deep Dive
Concomitant use of oral ketoconazole together with a CYP3A4 substrate known to prolong the QT interval, such as toremifene is contraindicated, as it may increase toremifene exposure, increasing the risk for QT prolongation and life-threatening ventricular tachyarrhythmias, including torsades de pointes1, which may result in syncope, seizure, and/or death. Interrupt toremifene therapy if possible during use of ketoconazole (a CYP3A4 inhibitor), and If interruption of treatment with toremifene is not possible, closely monitor patients for prolongation of QT interval 2.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated metabolism of toremifene; additive QT interval prolongation
Literature reports
1 report — tap to read
a) In a study of 18 healthy subjects, concomitant use of toremifene (a CYP3A4 substrate) 80 mg once daily with ketoconazole (a strong CYP3A4 inhibitor) 200 mg twice daily resulted in an increase in Cmax and AUC of toremifene by 1.4-fold and 2.9-fold, respectively 2.
Common questions
Can I take Toremifene and Ketoconazole Topical together?
Increased toremifene exposure and an increased risk of QT interval prolongation, ventricular tachycardia or torsade de pointes Always confirm with your pharmacist or prescriber before making any change.
How serious is the Toremifene 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 Toremifene 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 (2)
- Product Information: Ketoconazole oral tablet, ketoconazole oral tablet. Taro Pharmaceuticals U.S.A. Inc. (per DailyMed), Hawthorne, NY, 2024. DailyMed
- Product Information: Toremifene Citrate oral tablets, toremifene citrate oral tablets. Novadoz Pharmaceuticals LLC. (per DailyMed), Piscataway, NJ, 2025. DailyMed
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