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Warfarin, also known by the brand names Coumadin among others, is an anticoagulant normally used in the prevention of thrombosis and thromboembolism, the formation of blood clots in the blood vessels and their migration elsewhere in the body, respectively. It was initially introduced in 1948 as a pesticide against rats and mice, and is still used for this purpose, although more potent poisons such as brodifacoum have since been developed. In the early 1950s, warfarin was found to be effective and relatively safe for preventing thrombosis and thromboembolism in many disorders. It was approved for use as a medication in 1954, and has remained popular ever since. Warfarin is the most widely prescribed oral anticoagulant drug in North America.〔 Despite its effectiveness, treatment with warfarin has several shortcomings. Many commonly used medications interact with warfarin, as do some foods (particularly leaf vegetable foods or "greens," since these typically contain large amounts of vitamin K1) and its activity has to be monitored by blood testing for the international normalized ratio (INR) to ensure an adequate yet safe dose is taken. A high INR predisposes patients to an increased risk of bleeding, while an INR below the therapeutic target indicates the dose of warfarin is insufficient to protect against thromboembolic events. Warfarin and related 4-hydroxycoumarin-containing molecules decrease blood coagulation by inhibiting vitamin K epoxide reductase, an enzyme that recycles oxidized vitamin K1 to its reduced form after it has participated in the carboxylation of several blood coagulation proteins, mainly prothrombin and factor VII. Despite being labeled a vitamin K antagonist,〔 warfarin does not antagonize the action of vitamin K1, but rather antagonizes vitamin K1 recycling, depleting active vitamin K1.〔Holford NH. Clinical pharmacokinetics and pharmacodynamics of warfarin. Understanding the dose-effect relationship. Clin Pharmacokinet 1986; 11: 483–504.〕 Thus, the pharmacologic action may always be reversed by fresh vitamin K1. When administered, these drugs do not anticoagulate blood immediately. Instead, onset of their effect requires about two to three days before remaining active clotting factors have had time to naturally disappear in metabolism, and the duration of action of a single dose of warfarin is 2 to 5 days. Reversal of warfarin's effect by discontinuing its use, or by administering vitamin K1, requires a similar period of time. Warfarin is a synthetic derivative of dicoumarol, a 4-hydroxycoumarin-derived mycotoxin anticoagulant originally discovered in spoiled sweet clover-based animal feeds. Dicoumarol, in turn, is derived from coumarin, a sweet-smelling but coagulation-inactive chemical found naturally in "sweet" clover (to which it gives its odor and name), tonka beans (also known as "cumaru" from which coumarin's name derives), and many other plants. The name 'warfarin' stems from its discovery at the University of Wisconsin, incorporating the acronym for the organization that funded the key research, "WARF" for the Wisconsin Alumni Research Foundation and the ending "-arin", indicating its link with coumarin. ==Medical uses== Warfarin is used to decrease the tendency for thrombosis or as secondary prophylaxis (prevention of further episodes) in those individuals who have already formed a blood clot (thrombus). Warfarin treatment can help prevent formation of future blood clots and help reduce the risk of embolism (migration of a thrombus to a spot where it blocks blood supply to a vital organ).〔(【引用サイトリンク】url=http://www.drugs.com/monograph/coumadin.html )〕 Warfarin is best suited for anticoagulation (clot formation inhibition) in areas of slowly running blood (such as in veins and the pooled blood behind artificial and natural valves) and in blood pooled in dysfunctional cardiac atria. Thus, common clinical indications for warfarin use are atrial fibrillation, the presence of artificial heart valves, deep venous thrombosis, and pulmonary embolism (where the embolized clots first form in veins). Warfarin is also used in antiphospholipid syndrome. It has been used occasionally after heart attacks (myocardial infarctions), but is far less effective at preventing new thromboses in coronary arteries. Prevention of clotting in arteries is usually undertaken with antiplatelet drugs, which act by a different mechanism from warfarin (which normally has no effect on platelet function). 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「warfarin」の詳細全文を読む スポンサード リンク
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