Heparin is an anticoagulant drug which is used for the prophylaxis and treatment of venous thromboembolism and for the treatment of some cases of arterial thromboembolism. Venous thromboembolism is the commonest preventable cause of death in hospitalized patients, and the best approach to reduce its morbidity and mortality is the use of safe, effective, prophylaxis in patients at high risk. The use of low doses of heparin given s.c. (5000 units, 8 hourly)) has been shown in prospective clinical trials to be effective prophylaxis against venous thrombosis and nonfatal and fatal pulmonary embolism in patients undergoing general abdominothoracic surgery, without producing dangerous bleeding. Low-dose heparin, however, is not totally effective in patients undergoing hip surgery and suprapubic prostatectomy. The lack of benefit in these patients may be related to the intensity of the provocation to thrombosis. The use of heparin in large doses to treat thrombosis is associated with hemorrhagic complications in up to 30% of patients. There is evidence that continuous i.v. heparin is associated with fewer hemorrhagic complications than intermittent i.v. heparin, but the frequency is not related to the dose or to the use of laboratory monitoring. Hemorrhagic complications occur more frequently in elderly patients and in females and is more common following surgical operations. The frequency of recurrent venous thromboembolism is low in patients on therapeutic doses of heparin, and there is no difference in the frequency of recurrence in patients receiving heparin by continuous i.v. or intermittent i.v. administration.
