Drug interactions
Estradiol + Fosphenytoin
Severity: Major
Estradiol and Fosphenytoin: 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
Phenytoin, the active metabolite of fosphenytoin, is a strong enzyme inducer that increases estradiol clearance and lowers its levels. This can cause loss of efficacy and breakthrough bleeding, and contraceptive failure has been reported with hormonal products.
What this interaction means in plain words
Estradiol and Fosphenytoin 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.
Estradiol belongs to Endocrine; Fosphenytoin belongs to Central Nervous System.
Why it happens
Induction of CYP3A4 and possibly P-glycoprotein by phenytoin, increasing estradiol metabolism.
What to do
Use a non-hormonal or alternative contraceptive method when contraception is needed. For menopausal therapy, monitor for reduced effect and increase the estradiol dose if required.
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 Estradiol
- Anastrozole + Estradiol Contraindicated
- Estradiol + Fezolinetant Contraindicated
- Estradiol + Ospemifene Contraindicated
- Antithrombin alfa + Estradiol Major
- Antithrombin iii + Estradiol Major
- Estradiol + Exemestane Major
Other interactions of Fosphenytoin
- Dronedarone + Fosphenytoin Contraindicated
- Fosphenytoin + Ledipasvir-sofosbuvir Contraindicated
- Fosphenytoin + Lorlatinib Contraindicated
- Fosphenytoin + Lurasidone Contraindicated
- Fosphenytoin + Ranolazine Contraindicated
- Fosphenytoin + Sofosbuvir-velpatasvir-voxilaprevir Contraindicated
Frequently asked questions
Can I take Estradiol with Fosphenytoin?
MediHelp rates the interaction as major. Estradiol and Fosphenytoin 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. Phenytoin, the active metabolite of fosphenytoin, is a strong enzyme inducer that increases estradiol clearance and lowers its levels. This can cause loss of efficacy and breakthrough bleeding, and contraceptive failure has been reported with hormonal products.
How serious is the interaction between Estradiol and Fosphenytoin?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Use a non-hormonal or alternative contraceptive method when contraception is needed. For menopausal therapy, monitor for reduced effect and increase the estradiol dose if required.
What other medicines interact with Estradiol?
MediHelp also lists interactions of Estradiol with, for example, Anastrozole, Fezolinetant, Ospemifene. The full list is on the Estradiol page.
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