Drug interactions
Conjugated estrogens + Phenytoin
Severity: Moderate
Conjugated estrogens and Phenytoin: 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
Phenytoin induces estrogen metabolism and can reduce estrogen levels, causing loss of symptom control in hormone therapy. If used for contraception, efficacy may be lost, increasing the risk of unintended pregnancy.
What this interaction means in plain words
Conjugated estrogens and Phenytoin 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
Phenytoin induces CYP3A4 and other hepatic enzymes, increasing estrogen clearance.
What to do
Monitor for recurrence of menopausal symptoms or breakthrough bleeding and increase the estrogen dose if needed. Use a non-hormonal or alternate contraceptive method when contraception is needed.
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 Phenytoin
- Artemether / lumefantrine + Phenytoin Contraindicated
- Bictegravir + Phenytoin Contraindicated
- Cabotegravir + Phenytoin Contraindicated
- Doravirine + Phenytoin Contraindicated
- Elbasvir / grazoprevir + Phenytoin Contraindicated
- Elvitegravir / cobicistat / emtricitabine / tenofovir df + Phenytoin Contraindicated
Frequently asked questions
Can I take Conjugated estrogens with Phenytoin?
MediHelp rates the interaction as moderate. Conjugated estrogens and Phenytoin 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. Phenytoin induces estrogen metabolism and can reduce estrogen levels, causing loss of symptom control in hormone therapy. If used for contraception, efficacy may be lost, increasing the risk of unintended pregnancy.
How serious is the interaction between Conjugated estrogens and Phenytoin?
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 recurrence of menopausal symptoms or breakthrough bleeding and increase the estrogen dose if needed. Use a non-hormonal or alternate contraceptive method when contraception is needed.
What other medicines interact with Phenytoin?
MediHelp also lists interactions of Phenytoin with, for example, Artemether / lumefantrine, Bictegravir, Cabotegravir. The full list is on the Phenytoin page.
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