warfarin

Warfarin

Warfarin, sold under the brand name Coumadin among others, is used as an anticoagulant medication. It is commonly used to prevent deep vein thrombosis and pulmonary embolism, and to protect against stroke in people who have atrial fibrillation, valvular heart disease, or artificial heart valves. Warfarin may sometimes be prescribed following a ST-segment elevation myocardial infarction and orthopedic surgery. It is usually taken by mouth, but may also be administered intravenously. The common side effect, a natural consequence of reduced clotting, is bleeding. Less common side effects may include areas of tissue damage, and purple toes syndrome. Use is not recommended during pregnancy. The effects of warfarin are typically monitored by checking prothrombin time (INR) every one to four weeks. Many other medications and dietary factors can interact with warfarin, either increasing or decreasing its effectiveness. The effects of warfarin may be reversed with phytomenadione (vitamin K1), fresh frozen plasma, or prothrombin complex concentrate. Warfarin decreases blood clotting by blocking vitamin K epoxide reductase, an enzyme that reactivates vitamin K1. Without sufficient active vitamin K1, the plasma concentrations of clotting factors II, VII, IX, and X are reduced and thus have decreased clotting ability. The anticlotting protein C and protein S are also inhibited, but to a lesser degree. It is wrongly described as a "vitamin K antagonist". This term is incorrect. Warfarin does not antagonize the action of vitamin K1, but rather antagonizes vitamin K1 recycling, depletin...