Drug interactions
Fosamprenavir + Tamoxifen
Severity: Moderate
Fosamprenavir 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
Fosamprenavir (as amprenavir) inhibits CYP3A4 and may alter tamoxifen metabolism. Tamoxifen's active metabolite endoxifen depends mainly on CYP2D6, so the net clinical effect on efficacy is uncertain. Tamoxifen could also modestly affect antiretroviral levels.
What this interaction means in plain words
Fosamprenavir 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.
Why it happens
CYP3A4 inhibition alters tamoxifen N-demethylation, changing metabolite profile.
What to do
Prefer an alternative antiretroviral if feasible. If combined, monitor for tamoxifen toxicity or reduced efficacy and clinical response.
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 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 Fosamprenavir with Tamoxifen?
MediHelp rates the interaction as moderate. Fosamprenavir 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. Fosamprenavir (as amprenavir) inhibits CYP3A4 and may alter tamoxifen metabolism. Tamoxifen's active metabolite endoxifen depends mainly on CYP2D6, so the net clinical effect on efficacy is uncertain. Tamoxifen could also modestly affect antiretroviral levels.
How serious is the interaction between Fosamprenavir 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: Prefer an alternative antiretroviral if feasible. If combined, monitor for tamoxifen toxicity or reduced efficacy and clinical response.
What other medicines interact with Tamoxifen?
MediHelp also lists interactions of Tamoxifen with, for example, Amiodarone, Anastrozole, Bupropion. The full list is on the Tamoxifen page.
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