Drug interactions
Levonorgestrel oral / ethinylestradiol / ferrous bisglycinate + Phenytoin
Severity: Major
Levonorgestrel oral / ethinylestradiol / ferrous bisglycinate and Phenytoin: 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 lowers the concentrations of contraceptive hormones, which can lead to contraceptive failure and breakthrough bleeding. This matters particularly because phenytoin is teratogenic.
What this interaction means in plain words
Levonorgestrel oral / ethinylestradiol / ferrous bisglycinate and Phenytoin 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
Induction of hepatic CYP3A4 by phenytoin increases the metabolism of ethinylestradiol and levonorgestrel.
What to do
Use a non-hormonal or non-affected method such as a copper IUD or levonorgestrel IUS instead, or add a barrier method. Continue backup contraception for 28 days after stopping phenytoin.
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 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 Levonorgestrel oral / ethinylestradiol / ferrous bisglycinate with Phenytoin?
MediHelp rates the interaction as major. Levonorgestrel oral / ethinylestradiol / ferrous bisglycinate and Phenytoin 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 lowers the concentrations of contraceptive hormones, which can lead to contraceptive failure and breakthrough bleeding. This matters particularly because phenytoin is teratogenic.
How serious is the interaction between Levonorgestrel oral / ethinylestradiol / ferrous bisglycinate and Phenytoin?
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 non-hormonal or non-affected method such as a copper IUD or levonorgestrel IUS instead, or add a barrier method. Continue backup contraception for 28 days after stopping phenytoin.
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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