Warfarin

Warfarin is an anticoagulant medication that can be given orally. It works by decreasing levels of activity vitamin K in the blood. Vitamin K is necessary for the synthesis of many coagulation factors, and by blocking their production, coagulation slows down.

Warfarin is a derivative of coumarin[?], a plant chemical found in low levels in licorice, lavender and various other species. As well as its use as an anticoagulant, warfarin-like compounds are used as rat poison.

Warfarin is slower acting than another common anticoagulant heparin, though it has a number of advantages. Heparin must be given by injection, so this cannot be done by the patient. Warfarin has a long half-life and needs only be given once a day. As well as these problems, heparin can also cause thrombocytopenia[?] (a decrease in platelets), which may cause bleeding. For these main reasons, hospitalised patients are usually given heparin initially, and are then moved on to warfarin.

Warfarin, too, does have side effects. It has a very narrow therapeutic range[?], which means the levels in the blood that are effective are close to the levels that cause bleeding. This means it is easy to over- or under-coagulate the patient. Warfarin's effects must be closely monitored, this is done by using the INR[?].

There are many drug-drug interactions with warfarin, and its metabolism varies greatly between patients. This makes finding the correct dosage difficult.

Warfarin cannot be given to pregnant women, especially in the first trimester, as it is a teratogen.

If an overdose of warfarin is made, the effects can be reverse by giving a vitamin K injection, or if necessary fresh frozen plasma[?] infusion to replace coagulation proteins.

Warfarin is given to people with a thrombosis tendency. This can prevent growth or embolism of a thrombus.