Drug reference
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.
Drug class
Cardiovascular (Anti Thrombotics)
Mechanism of action
Interferes with hepatic synthesis of vitamin K-dependent clotting factors II, VII, IX, and X, as well as proteins C and S; S-warfarin is 4 times more potent than R-warfarin Warfarin depletes functional vitamin K reserves, which in turn reduces synthesis of active clotting factors, by competitively inhibiting subunit 1 of the multi-unit vitamin K
Common side effects
- Alopecia
- Rash
- Flatulence
- Cholesterol embolus syndrome
- Intraocular hemorrhage
- Abdominal pain
Boxed warnings
- Warfarin sodium can cause major or fatal bleeding; bleeding is more likely to occur during the starting period and with a higher dose (resulting in a higher INR) Risk factors for bleeding include high intensity of anticoagulation (INR greater than 4), age 65 years or older, highly variable INRs, history of gastrointestinal bleeding, hypertension, cerebrovascular disease, serious heart disease, anemia, malignancy, trauma, renal insufficiency, concomitant drugs, and long duration of warfarin therapy Regular monitoring of INR should be performed on all treated patients; those at high risk…
Contraindications
- Pregnancy, except in women with mechanical heart valves Hemorrhagic tendencies or blood dyscrasias Recent or contemplated CNS or eye surgery or traumatic surgery resulting in large open surfaces Bleeding tendencies associated with CNS hemorrhage, cerebral aneurysms, dissecting aorta, peric…
Known interactions (33)
- amiodarone + warfarin Major
- aspirin + warfarin Major
- aspirin (acetylsalicylic acid) + warfarin Major
- chloramphenicol + warfarin Major
- ciprofloxacin + warfarin Major
- clarithromycin + warfarin Major
- clopidogrel + warfarin Major
- fluconazole + warfarin Major
- heparin + warfarin Major
- ibuprofen + warfarin Major
- ketoconazole + warfarin Major
- metronidazole + warfarin Major
- NSAID + warfarin Major
- NSAIDs + warfarin Major
- Phylloquinone + warfarin Major
- prasugrel + warfarin Major
- rifampin + warfarin Major
- trimethoprim-sulfamethoxazole + warfarin Major
- acetaminophen + warfarin Moderate
- amoxicillin/clavulanate + warfarin Moderate
- azithromycin + warfarin Moderate
- ceftixone + warfarin Moderate
- ceftriaxone + warfarin Moderate
- Gliclazide + warfarin Moderate
- hydrocortisone + warfarin Moderate
- levofloxacin + warfarin Moderate
- omega-3 fatty acids (fish oil) + warfarin Moderate
- omeprazole + warfarin Moderate
- pantoprazole + warfarin Moderate
- paracetamol + warfarin Moderate
- proton pump inhibitor + warfarin Moderate
- statin + warfarin Moderate
- Trimethoprim + warfarin Moderate
Related conditions
Frequently asked questions
What drug class is warfarin?
warfarin belongs to: Cardiovascular.
How does warfarin work?
Interferes with hepatic synthesis of vitamin K-dependent clotting factors II, VII, IX, and X, as well as proteins C and S; S-warfarin is 4 times more potent than R-warfarin Warfarin depletes functional vitamin K reserves, which in turn reduces synthesis of active clotting factors, by competitively inhibiting subunit 1 of the multi-unit vitamin K
What are the common side effects of warfarin?
Alopecia, Rash, Flatulence, Cholesterol embolus syndrome, Intraocular hemorrhage, Abdominal pain
Which drugs interact with warfarin?
amiodarone, aspirin, aspirin (acetylsalicylic acid), chloramphenicol, ciprofloxacin, clarithromycin, clopidogrel, fluconazole, heparin, ibuprofen, ketoconazole, metronidazole, NSAID, NSAIDs, Phylloquinone
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