Known brand names include Jantoven and Coumadin.
An oral blood thinner that slows clot formation. It prevents and treats clots in the legs and lungs and prevents stroke from atrial fibrillation or artificial heart valves. Regular INR blood tests guide the dose.
Warfarin blocks an enzyme the body uses to recycle vitamin K. The body needs vitamin K to finish making several clotting proteins so they can work. With less recycled vitamin K, fewer working clotting proteins are made, and blood takes longer to clot. It also lowers proteins C and S, two natural proteins that help keep clotting in check.
Some blood-thinning effect usually starts within 24 hours, but the full effect can take 72 to 96 hours. A single dose keeps acting for 2 to 5 days, so the effect builds as daily doses overlap and lingers after the last one. Other drugs, changes in diet, and other factors can change how strongly it works. Because it slows clotting, its main danger is bleeding, which can be major or fatal.
Warfarin is a blood thinner taken as a pill that lowers the blood's ability to clot. It prevents and treats clots in the veins and clots that travel to the lungs, called pulmonary embolism. It also prevents clots in people with atrial fibrillation, a type of irregular heartbeat, or with a replaced heart valve. After a heart attack, it lowers the risk of death, another heart attack, and clot-related events such as stroke.
Its use in children rests on adult data and smaller observational studies, because well-controlled trials in children have not been done. People 60 or older tend to respond more strongly to it. Once a clot has formed, the aim is to keep it from growing and to prevent new clots and their complications. It has no direct effect on a clot that is already there, and it does not undo tissue damage from a blocked blood supply.
Easy bruising, nosebleeds, bleeding gums, and heavier periods are what people notice most. The label treats major bleeding as the main danger, especially in the first month. It also warns about rare skin death, painful purple toes, kidney injury, and gangrene in a limb when it is started during a certain immune reaction to heparin.
This is the boxed warning, the warning the FDA label prints first.
Bleeding risk. Warfarin can cause major or fatal bleeding. Monitor INR regularly in everyone. Drugs, diet, and other factors change the INR, and patients must be taught how to prevent and report bleeding.
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