Drug interactions
Tamoxifen + Terbinafine
Severity: Major
Tamoxifen and Terbinafine: 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
Tamoxifen requires CYP2D6 to form endoxifen, its most active metabolite. Terbinafine blocks this activation and may reduce the antiestrogenic effect, potentially compromising breast cancer treatment.
What this interaction means in plain words
Tamoxifen and Terbinafine 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.
Tamoxifen belongs to Endocrine; Terbinafine belongs to Anti Fungals.
Why it happens
Terbinafine inhibits CYP2D6, decreasing conversion of tamoxifen to endoxifen.
What to do
Avoid terbinafine in patients on tamoxifen and use an antifungal that does not inhibit CYP2D6, such as topical therapy where suitable or fluconazole with caution.
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 Terbinafine
- Terbinafine + Thioridazine Contraindicated
- Desipramine + Terbinafine Major
- Eliglustat + Terbinafine Major
- Flecainide + Terbinafine Major
- Imipramine + Terbinafine Major
- Maprotiline + Terbinafine Major
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 Tamoxifen with Terbinafine?
MediHelp rates the interaction as major. Tamoxifen and Terbinafine 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. Tamoxifen requires CYP2D6 to form endoxifen, its most active metabolite. Terbinafine blocks this activation and may reduce the antiestrogenic effect, potentially compromising breast cancer treatment.
How serious is the interaction between Tamoxifen and Terbinafine?
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 terbinafine in patients on tamoxifen and use an antifungal that does not inhibit CYP2D6, such as topical therapy where suitable or fluconazole with caution.
What other medicines interact with Terbinafine?
MediHelp also lists interactions of Terbinafine with, for example, Thioridazine, Desipramine, Eliglustat. The full list is on the Terbinafine page.
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