The rationale for long-term prophylaxis of venous thromboembolism.

Prophylaxis for venous thromboembolism (VTE) after surgery has traditionally been given from the time of surgery until hospital discharge, typically ranging from 5-14 days. Recently, there has been a trend toward shorter periods of hospitalization. Furthermore, a number of prospective studies have demonstrated that a significant proportion of patients develop deep vein thrombosis (DVT) or pulmonary embolism (PE) up to 5 or 6 weeks following general or orthopedic surgery. Therefore, prolonged prophylaxis during the post-discharge period may provide clinical benefits in high-risk patients. However, the optimal duration of prophylaxis for VTE after surgery remains unclear. In elective hip replacement, four studies of prolonged prophylaxis with low-molecular-weight heparin (LMWH) for 3- 4 weeks after hospital discharge demonstrated a significant reduction in the incidence of venography-confirmed DVT. These results support the use of prolonged thromboprophylaxis in the outpatient setting. Effective outpatient prophylaxis must be safe and convenient for patients to maximize compliance and clinical benefits. Low-molecular-weight heparins are safe and effective when given at a fixed daily dose, and pharmacoeconomic studies suggest that prolonged prophylaxis with these agents may be cost-effective. Key challenges for the future include identifying the patients who require prolonged prophylaxis and determining the duration of treatment.