Drug interactions
aspirin (acetylsalicylic acid) + warfarin
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.
Overview
Additive antithrombotic effects markedly increase bleeding risk (e.g., GI, intracranial); aspirin also impairs gastric mucosa. Combination generally avoided unless a clear indication exists.
Mechanism of action
Aspirin irreversibly inhibits platelet COX-1; warfarin reduces vitamin K–dependent clotting factors → additive anticoagulation/antiplatelet effect and GI mucosal injury.
Clinical management
Avoid routine combination. If necessary (e.g., mechanical valve, recent ACS), use lowest aspirin dose (≤81–100 mg/day), avoid other NSAIDs, consider PPI if GI risk, and monitor INR after start/stop (within 3–7 days) and for bleeding.
Drug reference
References
- Warfarin (Coumadin) Prescribing Information — FDA Label
- Warfarin: Drug information — Lexicomp
- Warfarin and other VKAs: Drug interactions — UpToDate
Frequently asked questions
Can I take aspirin (acetylsalicylic acid) with warfarin?
The interaction is rated: Major. Additive antithrombotic effects markedly increase bleeding risk (e.g., GI, intracranial); aspirin also impairs gastric mucosa. Combination generally avoided unless a clear indication exists.
How serious is the interaction between aspirin (acetylsalicylic acid) and warfarin?
The interaction is rated: Major. Evidence level: High.
How is the interaction between aspirin (acetylsalicylic acid) and warfarin managed?
Avoid routine combination. If necessary (e.g., mechanical valve, recent ACS), use lowest aspirin dose (≤81–100 mg/day), avoid other NSAIDs, consider PPI if GI risk, and monitor INR after start/stop (within 3–7 days) and for bleeding.
Why do aspirin (acetylsalicylic acid) and warfarin interact?
Aspirin irreversibly inhibits platelet COX-1; warfarin reduces vitamin K–dependent clotting factors → additive anticoagulation/antiplatelet effect and GI mucosal injury.
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