End points in studies on the prevention of deep vein thrombosis.

Clinically overt events are of obvious relevance for the outcome of patients. There is unanimous consensus of clinicians that these events should be prevented in clinical practice. In clinical trials on the prevention of deep vein thrombosis, symptomatic objectively confirmed venous thromboembolism is the most important outcome to be measured. However, because of the difficulties related to the measurement of clinically overt events, venography is the most commonly used method for end-point measurement in clinical trials on the prevention of venous thromboembolism. The limitations of venography leave a great need for the development of accurate noninvasive methods to be used as alternatives to venography. The end point must be tailored to the phase of the clinical trial. In phase I/II clinical trials, that are designed to evaluate the effectiveness of thromboprophylactic agents, it still is necessary to use the most accurate method for the diagnosis of deep vein thrombosis and to perform bilateral venography. When a new pharmacologic agent is compared with the gold standard agent, the use of symptomatic end points should be preferable.