Drug interactions
Fosphenytoin + Medroxyprogesterone
Severity: Major
Fosphenytoin and Medroxyprogesterone: 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
Fosphenytoin is converted to phenytoin, a potent enzyme inducer that speeds hormonal steroid metabolism. This may lower medroxyprogesterone concentrations and risks contraceptive failure or loss of therapeutic effect.
What this interaction means in plain words
Fosphenytoin and Medroxyprogesterone 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; Medroxyprogesterone belongs to Endocrine.
Why it happens
Phenytoin induces CYP3A4 and other hepatic enzymes, increasing clearance of medroxyprogesterone.
What to do
For contraception, consider a non-enzyme-inducer-affected method such as a copper IUD or levonorgestrel IUD, or add barrier methods. Shorter injection intervals are not well established, so confirm the plan with a specialist.
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 Medroxyprogesterone
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 Medroxyprogesterone?
MediHelp rates the interaction as major. Fosphenytoin and Medroxyprogesterone 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 potent enzyme inducer that speeds hormonal steroid metabolism. This may lower medroxyprogesterone concentrations and risks contraceptive failure or loss of therapeutic effect.
How serious is the interaction between Fosphenytoin and Medroxyprogesterone?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: For contraception, consider a non-enzyme-inducer-affected method such as a copper IUD or levonorgestrel IUD, or add barrier methods. Shorter injection intervals are not well established, so confirm the plan with a specialist.
What other medicines interact with Medroxyprogesterone?
MediHelp also lists interactions of Medroxyprogesterone with, for example, Bosentan, Brigatinib, Eslicarbazepine. The full list is on the Medroxyprogesterone page.
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