Comparison of Two Forms of the Anticlotting Drug Heparin for Treatment of Blood Clots in the Legs

Summaries for Patients are a service provided by Annals to help patients better understand the complicated and often mystifying language of modern medicine.

Summaries for Patients are presented for informational purposes only. These summaries are not a substitute for advice from your own medical provider. If you have questions about this material, or need medical advice about your own health or situation, please contact your physician.

The summary below is from the full report titled "Subcutaneous Enoxaparin Once or Twice Daily Compared with Intravenous Unfractionated Heparin for Treatment of Venous Thromboembolic Disease." It is in the 6 February 2001 issue of Annals of Internal Medicine (volume 134, pages 191-202). The authors are G Merli, TE Spiro, C-G Olsson, U Abildgaard, BL Davidson, A Eldor, D Elias, A Grigg, D Musset, GM Rodgers, AA Trowbridge, RD Yusen, and K Zawilska, for the Enoxaparin Clinical Trial Group.

What is the problem and what is known about it so far?

Deep venous thrombosis (DVT) is a condition in which blood clots form in the large leg veins, causing pain and swelling. It is important to treat DVT because clots can break off and travel through the bloodstream to the lungs, a potentially deadly condition called pulmonary embolism. DVT is most commonly treated with blood thinners, usually starting with standard heparin given intravenously (through a small tube inserted into a vein) for 5 to 10 days, followed by warfarin, a pill that is generally taken for at least 3 months. A new type of blood thinner called low-molecular-weight heparin has recently become available. Treatment with low-molecular-weight heparin is more convenient since it can simply be injected under the skin once or twice a day. In addition, unlike patients receiving standard heparin, patients receiving low-molecular-weight heparin do not need frequent blood tests to guide dose changes. Several studies have suggested that low-molecular-weight heparin is an effective treatment for DVT. However, those studies were small, did not include patients who had DVT plus pulmonary embolism, and used two injections per day rather than one.

Why did the researchers do this particular study?

To find out whether once-a-day injections of enoxaparin (a particular type of low-molecular-weight heparin) were as effective in the treatment of DVT (with or without pulmonary embolism) as intravenous heparin or twice-a-day injections of enoxaparin.

Who was studied?

The study included 900 patients with DVT cared for at 74 hospitals in 16 countries. Of the 900 patients, 287 also had pulmonary embolism.

How was the study done?

As soon as DVT was diagnosed, patients were randomly assigned to receive either standard heparin intravenously, two 1-milligram injections of enoxaparin per day, or one 1.5-milligram injection of enoxaparin per day. Patients also began taking oral blood thinners within 72 hours of entering the study.

What did the researchers find?

Symptoms of DVT returned with equal frequency in the three treatment groups; no difference was noted in the frequency of bleeding complications with the three types of treatment.

What were the limitations of the study?

Some patients with DVT would have been too sick to be eligible for the study, so it is unclear whether these results would apply to all patients with this condition. Of the 900 patients, only 740 completed enough of the study to be included in the analysis.

What are the implications of the study?

In the treatment of DVT (with or without pulmonary embolism), injection of enoxaparin once or twice daily appears to be as effective as intravenous heparin and does not cause more bleeding complications.