The Design of Venous Thromboembolism Prophylaxis Trials: Is Enoxaparin More Effective Than Fondaparinux?

The aim of thromboprophylaxis is to minimise the incidence of clinically relevant venous thromboembolism (VTE) but in many trials designed to determine the efficacy of thromboprophylactic agents, asymptomatic VTE is included in the primary endpoint. Since asymptomatic events occur much more frequently than symptomatic events, they dominate the results. Data from trials comparing the thromboprophylactic efficacy of enoxaparin and fondaparinux in orthopaedic surgical patients are used to demonstrate that asymptomatic and symptomatic endpoints may yield different conclusions. There was no difference between these agents in the incidence of symptomatic VTE. Efficacy and safety results of thromboprophylactic studies are affected by other aspects of trial design such as the dose of each agent and the timing of treatment initiation and endpoint assessment. Such factors should be considered when designing clinical trials and evaluating their results.