Warfarin at a glance
Medicine class
Vitamin K antagonist anticoagulant.
Monitoring
Regular INR blood tests check its anticoagulant effect and guide prescribing.
Administration
Follow your current anticoagulant instructions. Tablets and oral suspension may be taken with or without food.
Safety record
Carry your anticoagulant alert card and show it before medical or dental treatment.
What is Warfarin used for?
Selected UK products are licensed for:
Preventing systemic embolism in rheumatic heart disease and atrial fibrillation.
Preventing embolism after insertion of a prosthetic heart valve.
Preventing and treating venous thrombosis and pulmonary embolism.
Transient attacks of cerebral ischaemia; this appears in the selected tablet information but not the selected oral-suspension information.
How does Warfarin work?
Warfarin interferes with vitamin K recycling in the liver, reducing production of active clotting factors II, VII, IX and X. This makes clots less likely to form or extend but does not directly dissolve an established clot.
Warfarin preparations and strengths
Oral suspension
Route: Oral
Strengths: 1 mg/1 mL
Tablet
Route: Oral
Strengths: 0.5 mg, 5 mg
How to take Warfarin
Follow the current instructions in your anticoagulant record rather than an old label. It may be taken with or without food. Keep your intake of vitamin K-containing foods reasonably consistent and ask before making major dietary changes or starting medicines, supplements or herbal remedies.
Measure oral suspension with the supplied device, not a household spoon.
The selected tablet’s score line is not intended for dividing it.
Carry your anticoagulant alert card and tell doctors, dentists and pharmacists that you take warfarin.
Warfarin side effects
Common or expected effects
- Bruising or bleeding more easily, including nosebleeds, bleeding gums or heavier menstrual bleeding.
- Minor bleeding taking longer to stop.
Get urgent medical advice
- Major or internal bleeding, including blood in urine, black stools, or vomiting or coughing blood.
- Sudden severe headache, confusion, slurred speech, weakness, seizures or loss of consciousness.
- Painful red, purple, blue or black skin changes, including skin necrosis, purple-toe syndrome or calciphylaxis.
- Severe allergic reaction with swelling or breathing difficulty.
Warfarin in pregnancy
Warfarin is usually avoided during pregnancy because it can cause fetal abnormalities or bleeding. The selected suspension is contraindicated throughout pregnancy, while the selected tablet information specifies the first and third trimesters. Pregnancy exposure needs prompt specialist review. Tell the prescriber immediately if pregnant, planning pregnancy or pregnancy is possible, but do not stop warfarin without medical advice.
Warfarin while breastfeeding
Warfarin can generally be used while breastfeeding and is the preferred oral anticoagulant when clinically appropriate because milk transfer is negligible and no infant adverse effects have been reported. Seek advice for unexplained infant bruising or blood in urine, stools or vomit. Specialist assessment is particularly important for premature or unwell infants.
Warfarin interactions
Warfarin has a narrow therapeutic range. Check all medicine changes with the prescriber, anticoagulant clinic or pharmacist because additional INR monitoring may be needed.
NSAIDs and aspirin
Ibuprofen, aspirin and related medicines can increase bleeding risk; combine only when specifically directed.
Other anticoagulants or antiplatelet medicines
Heparins, rivaroxaban, dabigatran or clopidogrel can substantially increase bleeding risk.
Miconazole and other azole antifungals
They may markedly increase warfarin’s effect and INR, causing serious bleeding.
Common questions about Warfarin
Answers are fully visible for fast scanning and source review.
Why do I need INR blood tests?
INR shows how long your blood takes to clot and helps the anticoagulant service keep warfarin’s effect within the range selected for your condition.
Can I eat green vegetables?
Yes. Keep the amount reasonably consistent because sudden changes in vitamin K-rich foods can alter anticoagulant control.
Can I drink alcohol?
Sources
These sources were used to prepare and review this medicine page.
Prepared and reviewed by the iatroX editorial team.