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Chapter: Modern Pharmacology with Clinical Applications: Anticoagulant, Antiplatelet, and Fibrinolytic (Thrombolytic) Drugs

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Clinical Indications for Anticoagulant Therapy

Anticoagulant therapy provides prophylactic treatment of venous and arterial thromboembolic disorders.

CLINICAL INDICATIONS FOR ANTICOAGULANT THERAPY

Anticoagulant therapy provides prophylactic treatment of venous and arterial thromboembolic disorders. Anticoagulant drugs are ineffective against already formed thrombi, although they may prevent their fur-ther propagation. Generally accepted major indications for anticoagulant therapy with heparin and warfarin in-clude the following:

Deep Vein Thrombosis

Venous stasis resulting from prolonged bed rest, cardiac failure, or pelvic, abdominal, or hip surgery may precipi-tate thrombus formation in the deep veins of the leg or calf and may lead to fatal pulmonary embolism. Heparin may also be used prophylactically following surgery.

Arterial Embolism

Since arterial emboli formation involves platelet aggre-gation and leukocyte and erythrocyte infiltration into the fibrin network, the treatment and prophylaxis of arterial thrombi are more difficult. Arterial embolism is treated more successfully with heparin than with the oral antico-agulants. Anticoagulants are useful for prevention of sys-temic emboli resulting from valvular disease (rheumatic heart disease) and from valve replacement.

Atrial Fibrillation

Restoration of sinus rhythm in atrial fibrillation may dislodge thrombi that have developed as a result of stasis in the enlarged left atrium. The risk of stroke and systemic arterial embolism is decreased by anticoagula-tion in such patients.

Unstable Angina and Myocardial Infarction

In patients with unstable angina and severe ischemia re-quiring hospital admission, therapeutic doses of heparin along with antiplatelet therapy (discussed later) are thought to provide additive protection of the patient against myocardial reinfarction. Thrombolytic drugs are more effective than anticoagulants in treating coronary thromboembolism and in establishing reperfusion of oc-cluded arteries after an infarction. Anticoagulants in combination with antiplatelet drugs reduce the inci-dence of thrombus formation and reocclusion after coronary arterial bypass surgery and percutaneous coronary angioplasty.

Disseminated Intravascular Coagulation

Disseminated intravascular coagulation is characterized by widespread systemic activation of the coagulation system, consumption of coagulation factors, occlusion of small vessels by a coat of fibrin, and a hypocoagulation state with bleeding. In conjunction with management of the underlying factor or factors leading to the disorder and coagulation factor and platelet replacement, bleed-ing may be managed with intravenous (IV) heparin, LMWH, and antithrombin III (Thrombate).

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