Drug interactions
Ketoconazole + Toremifene
Severity: Major
Ketoconazole and Toremifene: major interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Ketoconazole raises toremifene exposure, which increases the risk of dose-related QT prolongation and torsades de pointes. Both drugs also carry intrinsic QT-prolonging potential, so the effects can be additive.
What this interaction means in plain words
Ketoconazole and Toremifene can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Ketoconazole belongs to Anti Fungals; Toremifene belongs to Endocrine.
Why it happens
Ketoconazole strongly inhibits CYP3A4, the main enzyme metabolizing toremifene, and both drugs also prolong the QT interval.
What to do
Avoid the combination where possible and use a non-interacting antifungal. If it cannot be avoided, obtain a baseline and follow-up ECG, correct potassium and magnesium, and consider reducing the toremifene dose.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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Other interactions of Ketoconazole
- Alfuzosin + Ketoconazole Contraindicated
- Alprazolam + Ketoconazole Contraindicated
- Avanafil + Ketoconazole Contraindicated
- Conivaptan + Ketoconazole Contraindicated
- Dihydroergotamine intranasal + Ketoconazole Contraindicated
- Dihydroergotamine + Ketoconazole Contraindicated
Other interactions of Toremifene
- Amiodarone + Toremifene Contraindicated
- Dronedarone + Toremifene Contraindicated
- Nilotinib + Toremifene Contraindicated
- Pimozide + Toremifene Contraindicated
- Quinidine + Toremifene Contraindicated
- Ribociclib + Toremifene Contraindicated
Frequently asked questions
Can I take Ketoconazole with Toremifene?
MediHelp rates the interaction as major. Ketoconazole and Toremifene can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Ketoconazole raises toremifene exposure, which increases the risk of dose-related QT prolongation and torsades de pointes. Both drugs also carry intrinsic QT-prolonging potential, so the effects can be additive.
How serious is the interaction between Ketoconazole and Toremifene?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid the combination where possible and use a non-interacting antifungal. If it cannot be avoided, obtain a baseline and follow-up ECG, correct potassium and magnesium, and consider reducing the toremifene dose.
What other medicines interact with Ketoconazole?
MediHelp also lists interactions of Ketoconazole with, for example, Alfuzosin, Alprazolam, Avanafil. The full list is on the Ketoconazole page.
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