Warfarin

What it is

Warfarin is an oral anticoagulant. It blocks vitamin K recycling in the liver, so the clotting factors that depend on vitamin K are made in an inactive form and blood clots more slowly. It is used to treat and prevent thrombosis and to reduce stroke risk in conditions that throw clots.

A usual adult range, not a national label — the dose and the timing differ by country and by product.

Used for

• Thrombosis
• Stroke prevention

Approved uses differ by country — some of these may be off-label or unapproved where you live.

What to know while taking it

It is usually taken in the evening so a dose can be adjusted the same day the INR result arrives, and INR has to be checked regularly because the effect drifts. Vitamin K intake from greens should stay steady rather than be avoided, since it is the swings that move the INR; alcohol does the same and is not combined with it. Many common drugs shift the effect, including paracetamol, amoxicillin, azithromycin, fluconazole and omega-3 supplements, while acetylsalicylic acid, ibuprofen, diclofenac, naproxen, ketorolac and clopidogrel add bleeding risk on top and are avoided. Hemoglobin and platelets are followed alongside the INR.

When to see a doctor

Black or bloody stools, blood in urine or vomit, coughing blood, unexplained bruising, a nosebleed that will not stop, or any head injury are reasons to see a doctor at once.

Worth knowing

• Raises bleeding risk
• Keep vitamin K intake steady
• INR must be checked regularly
• Do not combine with alcohol

Markers to watch

• Hemoglobin
• Platelets

Nutrients affected

• vitaminK — absorption blocked with