Risk-benefit assessment of anticoagulant therapy.

Thromboembolic disease is a common medical condition which, if untreated, carries a significant risk of morbidity and mortality. Treatment with anticoagulant therapy, while clearly beneficial, may expose patients to potentially serious side effects. A thoughtful risk-benefit assessment is therefore crucial before initiating therapy. Thromboembolic disease involves syndromes of both the venous and arterial circulation, and its pathogenesis is best understood by considering the elements of Virchow's Triad. This model defines the risk factors for venous thromboembolism and allows us to classify surgical and medical patients into low, moderate and high risk groups. Similar analysis allows risk assessment for patients prone to cardiogenic embolism resulting from nonvalvular atrial fibrillation, ischaemic heart disease, rheumatic heart disease and valvular prostheses. All anticoagulant therapy is prophylactic. Primary prophylaxis involves instituting anticoagulant therapy in patients at risk, before thromboembolism occurs, while secondary prophylaxis involves treating patients with established disease. The 2 major anticoagulants, heparin and warfarin, differ in their mechanism of action, mode of administration and methods of monitoring. Either may be used as primary or secondary prophylaxis. Heparin, because it acts immediately, is the drug of choice for the short term treatment of thromboembolic disease. Warfarin is the drug of choice for long term oral maintenance therapy. The principal complication of heparin therapy is haemorrhage, although thrombocytopenia and osteoporosis may also occur; the complications of warfarin include haemorrhage and skin necrosis. The risks of complications vary with the underlying thromboembolic disease. After the benefits of treatment are weighed against the risks of complications, recommendations for therapy can be established. The use of anticoagulants in pregnancy is especially complex. Here heparin is probably the preferred agent since, unlike warfarin, it does not cross the placenta and is nonteratogenic.