10 Anticoagulant therapy in venous thromboembolism

Abstract

After 50 years of clinical use, anticoagulants are still the mainstay of treatment for venous thromboembolism. The early experimental evidence that anticoagulants are of benefit in patients with pulmonary embolism came from the landmark study by Barritt and Jordon (1960). Following this, there were a number of descriptive studies supporting the use of anticoagulants in the treatment of venous thromboembolism. In the last decade, well designed randomized clinical trials became the accepted standard for making management decisions and, during this time, convincing evidence has emerged confirming and extending the effectiveness of anticoagulants in the treatment of venous thromboembolism. Hull et al (1979) and Lagerstedt et al (1985) performed randomized clinical trials which have established that patients with venous thrombosis who are treated with an initial course of intravenous heparin require continuing anticoagulant therapy for up to 3 months to prevent recurrence. In these two studies, patients randomized into inadequate treatment (5000 units heparin s.c. twice daily) (Hull et al, 1979) or no treatment (Lagerstedt et al, 1985) after an initial course of heparin, had a 29-47% incidence of recurrence compared to no recurrences in the groups randomized into oral anticoagulants. In 1986, Hull and associates demonstrated that failure to attain an adequate anticoagulant effect with heparin in patients with proximal vein thrombosis is associated with a high rate of recurrence, while clinically detectable recurrence is very low (< 2%) in patients whose activated partial thromboplastin time (APTT) and heparin levels are maintained in the therapeutic range (Hull et al, 1986).