Drug interactions
Fosphenytoin + Ulipristal
Severity: Major
Fosphenytoin 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
Fosphenytoin is converted to phenytoin, a strong CYP3A4 inducer, which can reduce ulipristal exposure. Emergency contraception may then fail.
What this interaction means in plain words
Fosphenytoin 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 ulipristal metabolism.
What to do
Avoid ulipristal and use a copper intrauterine device. Induction persists for weeks after stopping the inducer.
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 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 Fosphenytoin with Ulipristal?
MediHelp rates the interaction as major. Fosphenytoin 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. Fosphenytoin is converted to phenytoin, a strong CYP3A4 inducer, which can reduce ulipristal exposure. Emergency contraception may then fail.
How serious is the interaction between Fosphenytoin 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 and use a copper intrauterine device. Induction persists for weeks after stopping the inducer.
What other medicines interact with Fosphenytoin?
MediHelp also lists interactions of Fosphenytoin with, for example, Dronedarone, Ledipasvir-sofosbuvir, Lorlatinib. The full list is on the Fosphenytoin page.
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