Anticoagulant agents in the management of pulmonary embolism.

The anticoagulant agents most commonly used in the prevention and treatment of pulmonary embolism (PE) are unfractionated heparin, oral anticoagulants, and low molecular weight heparins (LMWHs). Unfractionated heparin at low fixed dose is the prophylactic regimen of choice for PE in patients undergoing general surgery or with serious medical diseases (low to moderate risk patients). In high risk patients perioperative prophylaxis with LMWHs or oral anticoagulants should be adopted. Therapy of pulmonary embolism should start with an intravenous bolus dose of 5000 U heparin followed by an infusion of 1250 U/h. Then the dose should be adjusted to maintain the aPTTX2-2.5 pre-treatment value. Heparin is continued for 7-10 days and is followed by oral anticoagulants for at least 3 months. Unfractionated heparin has some pharmacological limitations, mainly due to the aspecific binding to plasma proteins that limits its anticoagulant effect and causes the heparin resistance observed in some patients with PE and the inter-subject variability of the anticoagulant effect. Other antithrombotic agents such as LMWHs and selective thrombin inhibitors (hirudin and its analogues) do not aspecifically bind to plasma proteins. They have recently been used with promising results in the prevention and treatment of PE. Their definitive value in this clinical setting will be defined by the ongoing clinical trials.