Drug interactions
Phenindione + Phenytoin
Severity: Major
Phenindione 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
Phenindione may raise phenytoin levels, and phenytoin can change anticoagulant response, first potentiating and later reducing it. This makes INR control unpredictable and risks bleeding or thrombosis.
What this interaction means in plain words
Phenindione 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
Phenytoin displaces anticoagulants from protein binding and inhibits then induces their metabolism, while the anticoagulant may inhibit phenytoin metabolism.
What to do
Monitor INR frequently when starting, changing or stopping phenytoin, and adjust the anticoagulant dose. Check phenytoin levels for toxicity.
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 Phenindione with Phenytoin?
MediHelp rates the interaction as major. Phenindione 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. Phenindione may raise phenytoin levels, and phenytoin can change anticoagulant response, first potentiating and later reducing it. This makes INR control unpredictable and risks bleeding or thrombosis.
How serious is the interaction between Phenindione 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: Monitor INR frequently when starting, changing or stopping phenytoin, and adjust the anticoagulant dose. Check phenytoin levels for toxicity.
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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