Drug interactions
Primidone + Tamoxifen
Severity: Moderate
Primidone 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
Primidone, and its active metabolite phenobarbital, induce hepatic enzymes that convert tamoxifen to its metabolites. Exposure to tamoxifen and its active metabolite endoxifen may fall, which could weaken anti-estrogen effect.
What this interaction means in plain words
Primidone 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.
Primidone belongs to Central Nervous System; Tamoxifen belongs to Endocrine.
Why it happens
Induction of CYP3A4 and CYP2C9 by primidone/phenobarbital increases tamoxifen clearance.
What to do
Prefer a non-inducing anticonvulsant where possible. If the combination is needed, monitor for loss of tamoxifen efficacy and review the endocrine therapy plan with the oncologist.
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 Primidone
- Lorlatinib + Primidone Contraindicated
- Lurasidone + Primidone Contraindicated
- Primidone + Ranolazine Contraindicated
- Primidone + Sofosbuvir-velpatasvir-voxilaprevir Contraindicated
- Primidone + Voriconazole Contraindicated
- Abiraterone + Primidone Major
Frequently asked questions
Can I take Primidone with Tamoxifen?
MediHelp rates the interaction as moderate. Primidone 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. Primidone, and its active metabolite phenobarbital, induce hepatic enzymes that convert tamoxifen to its metabolites. Exposure to tamoxifen and its active metabolite endoxifen may fall, which could weaken anti-estrogen effect.
How serious is the interaction between Primidone 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 a non-inducing anticonvulsant where possible. If the combination is needed, monitor for loss of tamoxifen efficacy and review the endocrine therapy plan with the oncologist.
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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