Drug interactions
Fosphenytoin + Mifepristone
Severity: Major
Fosphenytoin and Mifepristone: 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, induces CYP3A4 and may substantially lower mifepristone exposure. This could lead to loss of mifepristone efficacy. Labeling advises against coadministration with CYP3A4 inducers.
What this interaction means in plain words
Fosphenytoin and Mifepristone 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 belongs to Central Nervous System; Mifepristone belongs to Endocrine.
Why it happens
Phenytoin induces CYP3A4, increasing mifepristone clearance.
What to do
Avoid concurrent use and consider an alternative anticonvulsant. If unavoidable, monitor for reduced mifepristone effect and check phenytoin levels.
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 Mifepristone
- Apixaban + Mifepristone Contraindicated
- Argatroban + Mifepristone Contraindicated
- Cisapride + Mifepristone Contraindicated
- Cortisone + Mifepristone Contraindicated
- Cyclosporin + Mifepristone Contraindicated
- Dabigatran etexilate + Mifepristone Contraindicated
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 Mifepristone?
MediHelp rates the interaction as major. Fosphenytoin and Mifepristone 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, induces CYP3A4 and may substantially lower mifepristone exposure. This could lead to loss of mifepristone efficacy. Labeling advises against coadministration with CYP3A4 inducers.
How serious is the interaction between Fosphenytoin and Mifepristone?
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 concurrent use and consider an alternative anticonvulsant. If unavoidable, monitor for reduced mifepristone effect and check phenytoin levels.
What other medicines interact with Mifepristone?
MediHelp also lists interactions of Mifepristone with, for example, Apixaban, Argatroban, Cisapride. The full list is on the Mifepristone page.
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