Drug interactions
Ketoconazole + Tamoxifen
Severity: Moderate
Ketoconazole and Tamoxifen: moderate 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 may alter tamoxifen metabolism and reduce formation of some metabolites, though the main efficacy-determining metabolite endoxifen depends mainly on CYP2D6. The clinical importance is uncertain, and both drugs can prolong the QT interval.
What this interaction means in plain words
Ketoconazole and Tamoxifen can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Ketoconazole belongs to Anti Fungals; Tamoxifen belongs to Endocrine.
Why it happens
Ketoconazole inhibits CYP3A4 and CYP2C9 metabolism of tamoxifen, with possible additive QT effects.
What to do
Monitor for changes in therapeutic response and consider an ECG in patients with QT risk factors. Choose an alternative antifungal for prolonged courses if feasible.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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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 Tamoxifen
- Amiodarone + Tamoxifen Major
- Anastrozole + Tamoxifen Major
- Bupropion + Tamoxifen Major
- Carbamazepine + Tamoxifen Major
- Cinacalcet + Tamoxifen Major
- Dacomitinib + Tamoxifen Major
Frequently asked questions
Can I take Ketoconazole with Tamoxifen?
MediHelp rates the interaction as moderate. Ketoconazole and Tamoxifen can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Ketoconazole may alter tamoxifen metabolism and reduce formation of some metabolites, though the main efficacy-determining metabolite endoxifen depends mainly on CYP2D6. The clinical importance is uncertain, and both drugs can prolong the QT interval.
How serious is the interaction between Ketoconazole and Tamoxifen?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor for changes in therapeutic response and consider an ECG in patients with QT risk factors. Choose an alternative antifungal for prolonged courses if feasible.
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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