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Vitamin K antagonists (VKA) are a group of substances that reduce blood clotting by reducing the action of vitamin K. They are used as rodenticides and as anticoagulant medications in the prevention of thrombosis. == Mechanism of action == These drugs deplete the active form of the vitamin by inhibiting the enzyme vitamin K epoxide reductase and thus the recycling of the inactive vitamin K epoxide back to the active reduced form of vitamin K. The drugs are structurally similar to vitamin K and act as competitive inhibitors of the enzyme. The term "vitamin K antagonist" is a misnomer, as the drugs do not directly antagonise the action of vitamin K in the pharmacological sense, but rather the recycling of vitamin K. Vitamin K is required for the proper production of certain proteins involved in the blood clotting process. For example, it is needed to carboxylate specific glutamic acid residues on prothrombin. Without these residues carboxylated, the protein will not form the appropriate conformation of thrombin, which is needed to produce the fibrin monomers that are polymerized to form clots. The action of this class of anticoagulants may be reversed by administering vitamin K for the duration of the anticoagulant's residence in the body, and the daily dose needed for reversal is the same for all drugs in the class. However, in the case of the second generation "super warfarins" intended to kill warfarin resistant rodents, the time of vitamin K administration may need to be prolonged to months, in order to combat the long residence time of the poison. The vitamin K antagonists can cause birth defects (teratogens). 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「Vitamin K antagonist」の詳細全文を読む スポンサード リンク
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