- Key People:
- Charles H. Best
- Related Topics:
- Atryn
- heparin
- warfarin
- discoumarol
- hirudin
anticoagulant
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What are anticoagulants?
Anticoagulants are drugs that prevent blood from clotting by suppressing the synthesis or function of clotting factors normally present in the blood. They are used to prevent blood clots in veins or arteries or to prevent the enlargement of a clot circulating in the bloodstream.
There are generally two types of anticoagulants:
* Heparin, which is given by injection
* Coumarin or indandione derivatives, which are administered orallyCoumarin derivatives resemble vitamin K and interfere with vitamin K metabolism in the liver, resulting in defective clotting factors incapable of binding calcium ions. Hemorrhage is the main toxic effect during oral anticoagulant therapy, and vitamin K can be administered intravenously to stop bleeding.
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Why does the body need anticoagulants?
Anticoagulants are essential to prevent the formation of blood clots (thrombi) in veins or arteries and to prevent the enlargement of existing clots in the bloodstream. They work by suppressing the synthesis or function of clotting factors normally present in the blood. Conditions treated with anticoagulants include deep-vein thrombosis, pulmonary embolism, coronary thrombosis, and disseminated intravascular coagulation. Some coagulation disorders can be caused by vitamin K deficiencies. Coumarin derivatives, a type of anticoagulant, resemble vitamin K and interfere with its metabolism in the liver, leading to defective clotting factors.
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How do anticoagulants affect blood clotting?
Anticoagulants are drugs that prevent blood from clotting by suppressing the synthesis or function of clotting factors normally present in the blood.
Coumarin derivatives, a type of oral anticoagulant, resemble vitamin K, which is needed to synthesize clotting factors. These derivatives interfere with vitamin K metabolism in the liver, resulting in defective clotting factors that cannot bind calcium ions, which are required for coagulation.
The normal hemostatic response to damage to the vascular endothelium can be organized into four stages: (1) initial vasoconstriction, (2) aggregation of platelets on and around the lesion and the formation of a platelet plug, (3) activation of the reactions of coagulation, and (4) the activation of fibrinolysis.
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What are some examples of natural anticoagulants in the body?
Natural anticoagulants are crucial for maintaining blood fluidity in the body. Antithrombin (AT) in blood plasma blocks thrombin, a key coagulation enzyme, and other activated clotting proteins, preventing clot formation. This process is enhanced by heparin, produced by connective tissue mast cells. Protein C, a vitamin K-dependent protein, inactivates factors VIII and V when activated by thrombin, and its function is enhanced by protein S, another vitamin K-dependent protein. Additionally, plasmin, derived from plasminogen, dissolves fibrin to remove clots. Deficiencies in antithrombin, protein C, or protein S can lead to excessive clotting.
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How do artificial anticoagulants (like medications) work differently from natural ones?
Artificial anticoagulants, like heparin and coumarin derivatives, are drugs that prevent blood from clotting by suppressing the synthesis or function of clotting factors. Heparin, given by injection, enhances antithrombin III, a plasma protein that inactivates clotting proteins. Coumarin derivatives, taken orally, interfere with vitamin K metabolism in the liver, leading to defective clotting factors.
Natural anticoagulants in the body, such as antithrombin III, protein C, and protein S, regulate the clotting process by inactivating active enzymes and dissolving fibrin. These natural anticoagulants ensure that after the blood-clotting system is activated, the clotting process is contained locally to the area of tissue injury.
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Why is it important to carefully control the amount of anticoagulant in a person’s body?
Anticoagulants are drugs that prevent blood from clotting by suppressing the synthesis or function of clotting factors normally present in the blood. They are used to prevent the formation of blood clots in veins or arteries or to prevent the enlargement of a clot circulating in the bloodstream.
Conditions treated with anticoagulants include deep-vein thrombosis, pulmonary embolism, coronary thrombosis, and disseminated intravascular coagulation. Bleeding disorders are suspected when blood is seen in the skin or when a wound is delayed in clotting.
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anticoagulant, any drug that, when added to blood, prevents it from clotting. Anticoagulants achieve their effect by suppressing the synthesis or function of various clotting factors that are normally present in the blood. Such drugs are often used to prevent the formation of blood clots (thrombi) in the veins or arteries or the enlargement of a clot that is circulating in the bloodstream. Conditions commonly treated with anticoagulants include deep-vein thrombosis, in which clots form in so-called deep veins, such as those of the legs; pulmonary embolism, in which a clot obstructs the pulmonary artery or one of its branches; coronary thrombosis, in which a clot obstructs a coronary artery in the heart; and disseminated intravascular coagulation, a systemic activation of the coagulation system that leads to the consumption of coagulation factors and hemorrhage. Anticoagulants are also used in drawing and storing blood.
Anticoagulants generally are of two types: heparin, which is given by injection, and derivatives of coumarin or indandione, which are administered orally.
Heparin
Heparin, used primarily in hospitalized patients, is a mixture of mucopolysaccharides that promote the activity of antithrombin III, a blood plasma protein that inactivates thrombin (an enzyme that promotes clotting). Because it is not well absorbed from the gastrointestinal tract, heparin is given intravenously to inhibit coagulation immediately, or it is given subcutaneously. Heparin is not bound to plasma proteins, it is not secreted into breast milk, and it does not cross the placenta. The drug’s action is terminated by metabolism in the liver and excretion by the kidneys. The major side effect associated with heparin is hemorrhage; thrombocytopenia (reduced number of circulating platelets) and hypersensitivity reactions also may occur. When oral anticoagulants are given with heparin, additional anticoagulant effects occur. Heparin-induced hemorrhage may be reversed with the antagonist protamine, a positively charged protein that has a high affinity for heparin’s negatively charged molecules, thus neutralizing the drug’s anticoagulant effect.
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Oral anticoagulants
Structurally, the coumarin derivatives resemble vitamin K, an important element in the synthesis of a number of clotting factors. Interference in the metabolism of vitamin K in the liver by coumarin derivatives gives rise to clotting factors that are defective and incapable of binding calcium ions (another important element in the activation of coagulation factors at several steps in the coagulation cascade). The other group of oral anticoagulants, the synthetic indandione derivatives (e.g., anisindione), are thought to work by a similar mechanism of action.
When anticoagulants are taken orally, several hours are required for the onset of the anticoagulant effect because time is required both for their absorption from the gastrointestinal tract and for the clearance of biologically active clotting factors from the blood. Warfarin, a coumarin derivative and the most commonly used oral anticoagulant, is rapidly and almost completely absorbed.
Oral anticoagulants differ from heparin primarily in their longer duration of action, which is the result of extensive binding to plasma proteins, giving these agents relatively long plasma half-lives. Oral anticoagulants are metabolized by the liver and excreted in the urine and feces. They may cross the placenta to cause fetal abnormalities or hemorrhages in newborns; however, their appearance in breast milk apparently has no adverse effect on nursing infants.
Hemorrhage is the principal toxic effect during oral anticoagulant therapy. Vitamin K, when given intravenously to promote the synthesis of functional clotting factors, stops bleeding after several hours. Plasma that contains normal clotting factors is given to control serious bleeding. Oral anticoagulants may interact adversely with other drugs that bind to plasma proteins or are metabolized by the liver.
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