Drug interactions
Idelalisib + Tamoxifen
Severity: Moderate
Idelalisib 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
Idelalisib is a strong CYP3A4 inhibitor and may alter tamoxifen metabolism, but tamoxifen's activation to endoxifen is mainly via CYP2D6 and exposure effects are uncertain. Idelalisib itself has serious toxicities, and the net interaction is unclear.
What this interaction means in plain words
Idelalisib 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.
Idelalisib belongs to Oncology; Tamoxifen belongs to Endocrine.
Why it happens
Idelalisib inhibits CYP3A4, reducing tamoxifen conversion to N-desmethyltamoxifen; clinical significance is not well established.
What to do
Monitor for reduced tamoxifen efficacy and for liver toxicity; consider alternative endocrine therapy if concerns arise.
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
Other interactions of Idelalisib
- Alfuzosin + Idelalisib Contraindicated
- Cisapride + Idelalisib Contraindicated
- Dihydroergotamine + Idelalisib Contraindicated
- Dronedarone + Idelalisib Contraindicated
- Eletriptan + Idelalisib Contraindicated
- Eplerenone + Idelalisib Contraindicated
Frequently asked questions
Can I take Idelalisib with Tamoxifen?
MediHelp rates the interaction as moderate. Idelalisib 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. Idelalisib is a strong CYP3A4 inhibitor and may alter tamoxifen metabolism, but tamoxifen's activation to endoxifen is mainly via CYP2D6 and exposure effects are uncertain. Idelalisib itself has serious toxicities, and the net interaction is unclear.
How serious is the interaction between Idelalisib 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 reduced tamoxifen efficacy and for liver toxicity; consider alternative endocrine therapy if concerns arise.
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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