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Recurrence of Venous Thromboembolism after Treatment with Unfractionated Heparin

TO THE EDITOR: The study by de Valk and colleagues [1] satisfactorily achieved the authors' stated goal of [defining] the optimal dose of danaparoid for further clinical testing in the treatment of venous thromboembolism. Their conclusion of superior efficacy, however, is based on a comparison with a sub-standard regimen for administering unfractionated heparin. Adequate dosing requires the use of a formal nomogram such as that of Raschke and colleagues [2]. Furthermore, therapeutic prolongation of the activated partial thromboplastin time must occur within 24 hours of the initiation of treatment [3]. The lack of an appropriate nomogram suggests that the target activated partial thromboplastin time was not achieved [4]. Consequently, the heparin recipients in de Valk and colleagues' study would be expected to have unacceptably high recurrence rates of deep venous thrombosis. Appropriately, achieving an acceptable international normalized ratio was required by de Valk and coworkers before cessation of heparin. However, the authors did not indicate that the necessary concurrent administration of oral anticoagulant and heparin for 3 to 5 days [5] had occurred. This essential aspect of treatment may have been only marginally achieved, given that initiation of therapy with oral anticoagulants was delayed for the initial 48 hours and that heparin was stopped after as few as 5 days of treatment. This factor may have adversely influenced recurrence rates. Stuart Keith Sutton, MD Health Services Association of Central New York Syracuse, NY 13224-1396