Drug interactions
Etonogestrel + Fosphenytoin
Severity: Major
Etonogestrel and Fosphenytoin: 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 strong enzyme inducer and substantially lowers progestin exposure, with reported contraceptive failures. The implant should not be relied upon alone.
What this interaction means in plain words
Etonogestrel and Fosphenytoin 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.
Etonogestrel belongs to Endocrine; Fosphenytoin belongs to Central Nervous System.
Why it happens
Strong induction of CYP3A4 by phenytoin accelerates etonogestrel clearance.
What to do
Use a copper IUD, levonorgestrel IUD or DMPA instead, or add condoms during therapy and for several weeks after stopping.
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 Etonogestrel
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 Etonogestrel with Fosphenytoin?
MediHelp rates the interaction as major. Etonogestrel and Fosphenytoin 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 strong enzyme inducer and substantially lowers progestin exposure, with reported contraceptive failures. The implant should not be relied upon alone.
How serious is the interaction between Etonogestrel and Fosphenytoin?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Use a copper IUD, levonorgestrel IUD or DMPA instead, or add condoms during therapy and for several weeks after stopping.
What other medicines interact with Etonogestrel?
MediHelp also lists interactions of Etonogestrel with, for example, Amobarbital, Armodafinil, Bosentan. The full list is on the Etonogestrel page.
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