Secondary prophylaxis with oral anticoagulant therapy - adapted from the New England Journal of Medi

Date: Oct, 1995

Although secondary prophylaxis with oral anticoagulants is used routinely to prevent recurrence of deep venous thrombosis and pulmonary embolism, the optimal duration of therapy is uncertain. Schulman and colleagues compared the effectiveness of six weeks of oral anticoagulant therapy with that of six months of therapy for secondary prophylaxis.

A total of 897 patients with a first episode of venous thromboembolism were included in the study. Oral anticoagulation consisted of treatment with warfarin or dicumarol, with a targeted international normalized ratio of 2.0 to 2.85.

Of the 123 recurrences of venous thromboembolism during the two years of followup, 80 occurred in the 443 patients who received six weeks of therapy (for an incidence of 18.1 percent) and 43 occurred among the 454 patients who received six months of therapy (for an incidence of 9.5 percent). The two groups did not differ significantly in mortality or in the incidence of major hemorrhage.

The authors conclude that six months of prophylactic oral anticoagulation after a first episode of venous thromboembolism reduces the rate of recurrence by half, compared with six weeks of therapy.

In a related editorial, Hirsh points out that data from prospective trials indicate that the risk of recurrent pulmonary embolism is lower among patients with a reversible risk factor, such as surgery or trauma, compared with those with a permanent risk factor, such as cancer or idiopathic deep venous thrombosis. Hirsh suggests that it may be reasonable for patients with reversible risk factors to receive six weeks of therapy and for those with idiopathic venous thrombosis or a permanent risk factor to receive up to six months of therapy. (New England Journal of Medicine, June 22, 1995, vol.332, pp. 1661, 1710.)

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