anticoagulant

anticoagulant

[an-tee-koh-ag-yuh-luhnt, an-tahy-]
anticoagulant, any of several substances that inhibit blood clot formation (see blood clotting). Some anticoagulants, such as the coumarin derivatives bishydroxycoumarin (Dicumarol) and warfarin (Coumadin) inhibit synthesis of prothrombin, a clot-forming substance, and other clotting factors. The coumarin derivatives compete with vitamin K, which is a necessary substance in prothrombin formation (see vitamin). They are only effective after the body's existing supply of prothrombin is depleted. Another anticoagulant, heparin, is a polysaccharide (see carbohydrate) found naturally in many cells. It acts in several ways: by preventing prothrombin formation; by preventing formation of fibrin, another clotting substance; and by decreasing the availability of a third clotting factor, thrombin. Heparin is obtained by extracting it from animal tissues. Anticoagulants are used to treat blood clots, which appear especially frequently in veins of the legs and pelvis in bedridden patients. Therapy helps to reduce the risk of clots reaching the lung, heart, or other organs. Heparin causes an instantaneous increase in blood-clotting time, and its effect lasts several hours.

Substance that prevents blood from clotting by suppressing the synthesis or function of various clotting factors (see coagulation). Anticoagulants are given to prevent thrombosis and used in drawing and storing blood. There are two main types of anticoagulants: heparin and vitamin K antagonists (e.g., warfarin). The latter have longer-lasting effects, interfering in the liver's metabolism of vitamin K to cause production of defective clotting factors. Anticoagulant therapy carries a high risk of uncontrollable hemorrhage.

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