Drug interactions
Phenytoin + Progesterone intravaginal
Severity: Major
Phenytoin and Progesterone intravaginal: 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 induces hepatic and intestinal CYP3A4 and can lower progesterone concentrations. This may reduce efficacy in luteal support or endometrial protection, with a risk of treatment failure.
What this interaction means in plain words
Phenytoin and Progesterone intravaginal 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.
Why it happens
Phenytoin induces CYP3A4, increasing the metabolic clearance of progesterone.
What to do
Consider a non-inducing antiseizure drug if clinically possible. If both are required, monitor for loss of progestogenic effect (breakthrough bleeding, pregnancy outcome, endometrial status) and use non-hormonal contraception where contraception is intended.
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 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 Phenytoin with Progesterone intravaginal?
MediHelp rates the interaction as major. Phenytoin and Progesterone intravaginal 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 induces hepatic and intestinal CYP3A4 and can lower progesterone concentrations. This may reduce efficacy in luteal support or endometrial protection, with a risk of treatment failure.
How serious is the interaction between Phenytoin and Progesterone intravaginal?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Consider a non-inducing antiseizure drug if clinically possible. If both are required, monitor for loss of progestogenic effect (breakthrough bleeding, pregnancy outcome, endometrial status) and use non-hormonal contraception where contraception is intended.
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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