Drug interactions
Primidone + Warfarin
Severity: Major
Primidone and Warfarin: major interaction.
Last updated Sources: UK SmPC
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
Primidone is metabolized to phenobarbital and is itself an enzyme inducer. It can speed warfarin clearance and lower INR, risking thrombosis, and stopping it can lead to INR rises.
What this interaction means in plain words
Primidone and Warfarin 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.
Primidone belongs to Central Nervous System; Warfarin belongs to Cardiovascular.
Why it happens
Hepatic enzyme induction, including CYP2C9, by primidone and its metabolite phenobarbital.
What to do
Check INR frequently after primidone is started, changed or stopped. Adjust warfarin to maintain the target range.
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?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Primidone and Warfarin, the additional notes, the evidence detail and the whole-prescription interaction checker.
- Full clinical management advice
- Additional notes
- Evidence detail
- Interaction checker for a whole prescription
Try Pro+ free for 7 days on the web. No card needed.
References
Other interactions of Warfarin
- Defibrotide + Warfarin Contraindicated
- Ketorolac + Warfarin Contraindicated
- Abciximab + Warfarin Major
- Acetylsalicylic acid + Warfarin Major
- Adagrasib + Warfarin Major
- Amiodarone + Warfarin Major
Other interactions of Primidone
- Lorlatinib + Primidone Contraindicated
- Lurasidone + Primidone Contraindicated
- Primidone + Ranolazine Contraindicated
- Primidone + Sofosbuvir-velpatasvir-voxilaprevir Contraindicated
- Primidone + Voriconazole Contraindicated
- Abiraterone + Primidone Major
Frequently asked questions
Can I take Primidone with Warfarin?
MediHelp rates the interaction as major. Primidone and Warfarin 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. Primidone is metabolized to phenobarbital and is itself an enzyme inducer. It can speed warfarin clearance and lower INR, risking thrombosis, and stopping it can lead to INR rises.
How serious is the interaction between Primidone and Warfarin?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Check INR frequently after primidone is started, changed or stopped. Adjust warfarin to maintain the target range.
What other medicines interact with Warfarin?
MediHelp also lists interactions of Warfarin with, for example, Defibrotide, Ketorolac, Abciximab. The full list is on the Warfarin page.
Full monographs, dosing and an interaction checker in the MediHelp app
Open the complete reference, check multi-drug interactions and use dosing tools in the MediHelp app.
