Drug interactions
Phenytoin + Ulipristal
Severity: Major
Phenytoin and Ulipristal: major interaction.
Last updated Sources: US FDA label
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 is a CYP3A4 inducer and can substantially lower ulipristal exposure. This may make emergency contraception less effective and raise the risk of unintended pregnancy.
What this interaction means in plain words
Phenytoin and Ulipristal 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 ulipristal.
What to do
Avoid ulipristal in patients taking phenytoin, or within about 4 weeks of stopping it, and use a copper intrauterine device as emergency contraception instead.
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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References
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 Ulipristal?
MediHelp rates the interaction as major. Phenytoin and Ulipristal 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 is a CYP3A4 inducer and can substantially lower ulipristal exposure. This may make emergency contraception less effective and raise the risk of unintended pregnancy.
How serious is the interaction between Phenytoin and Ulipristal?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid ulipristal in patients taking phenytoin, or within about 4 weeks of stopping it, and use a copper intrauterine device as emergency contraception instead.
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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