Drug interactions
Warfarin + Zafirlukast
Severity: Major
Warfarin and Zafirlukast: 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
Zafirlukast inhibits CYP2C9, the main enzyme that clears S-warfarin, and can raise the INR with increased risk of bleeding. Labeling and case reports describe enhanced anticoagulation with this combination.
What this interaction means in plain words
Warfarin and Zafirlukast 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.
Warfarin belongs to Cardiovascular; Zafirlukast belongs to Respiratory.
Why it happens
Zafirlukast inhibits CYP2C9-mediated metabolism of S-warfarin, increasing warfarin exposure.
What to do
Check the INR more frequently when starting or stopping zafirlukast and reduce the warfarin dose as needed. Educate the patient about bleeding signs.
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 Zafirlukast
- Pimozide + Zafirlukast Contraindicated
- Lomitapide + Zafirlukast Major
- Nilotinib + Zafirlukast Major
- Apalutamide + Zafirlukast Moderate
- Carbamazepine + Zafirlukast Moderate
- Conivaptan + Zafirlukast Moderate
Other interactions of Warfarin
- Defibrotide + Warfarin Contraindicated
- Ketorolac + Warfarin Contraindicated
- Abciximab + Warfarin Major
- Acetylsalicylic acid + Warfarin Major
- Adagrasib + Warfarin Major
- Amiodarone + Warfarin Major
Frequently asked questions
Can I take Warfarin with Zafirlukast?
MediHelp rates the interaction as major. Warfarin and Zafirlukast 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. Zafirlukast inhibits CYP2C9, the main enzyme that clears S-warfarin, and can raise the INR with increased risk of bleeding. Labeling and case reports describe enhanced anticoagulation with this combination.
How serious is the interaction between Warfarin and Zafirlukast?
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 the INR more frequently when starting or stopping zafirlukast and reduce the warfarin dose as needed. Educate the patient about bleeding signs.
What other medicines interact with Zafirlukast?
MediHelp also lists interactions of Zafirlukast with, for example, Pimozide, Lomitapide, Nilotinib. The full list is on the Zafirlukast page.
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