Fondaparinux or Enoxaparin for Deep Venous Thrombosis?

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The summary below is from the full report titled "Fondaparinux or Enoxaparin for the Initial Treatment of Symptomatic Deep Venous Thrombosis. A Randomized Trial." It is in the 1 June 2004 issue of Annals of Internal Medicine (volume 140, pages 867-873). The authors are H.R. Büller, B.L. Davidson, H. Decousus, A. Gallus, M. Gent, F. Piovella, M.H. Prins, G. Raskob, A.E.M. Segers, R. Cariou, O. Leeuwenkamp, and A.W.A. Lensing, for The Matisse Investigators.

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

A blood clot inside the deep veins of the legs causes deep venous thrombosis (DVT). Pieces of the clot can break off, travel to the lungs, and cause serious and even fatal complications. Doctors usually give blood thinners to patients with DVT for several months to prevent pieces of clots from breaking loose and to stop new clots from forming. Vitamin K antagonists (warfarin, also known by the brand name Coumadin) are blood thinners that can be taken by mouth, but they take about a week to adequately thin blood and block clotting. Thus, patients with DVT must take other blood thinners during the first several days after a vitamin K antagonist is given. For many years, doctors initiated therapy for DVT with a blood-thinning drug known as unfractionated heparin. They gave this drug through a needle in a vein for a few days while patients started vitamin K antagonist therapy in the hospital. More recently, doctors have been using another preparation of heparin, low-molecular-weight heparin (LMWH), or drugs that selectively block clotting (factor Xa inhibitor). Both LMWH and factor Xa inhibitors can be injected under the skin, can be given at home, and do not require close monitoring of the dose. Several studies show that both drugs are safe and effective for treating DVT, but we do not know whether one is better than the other.

Why did the researchers do this particular study?

To see whether fondaparinux (factor Xa inhibitor) and enoxaparin (LMWH) have similar safety and efficacy for treating DVT.

Who was studied?

2205 adults with symptomatic DVT from 154 centers worldwide.

How was the study done?

The researchers randomly assigned 2205 patients with DVT to receive either fondaparinux once daily or enoxaparin twice daily. Both drugs were injected under the skin for at least 5 days. The patients and their doctors did not know who received which drug. All patients were also given blood thinner pills (vitamin K antagonists) for 3 months. During that time, doctors routinely checked for complications, such as bleeding, and also for evidence of new or repeated clots in the legs, lungs, or both.

What did the researchers find?

About 1% of the patients in each group had a major bleeding complication during the first week or so of treatment. About 4% in each group had repeated clots within 3 months. About 3% to 4% in each group died during follow-up. Most of the deaths were due to causes other than the clots or bleeding.

What were the limitations of the study?

Most patients received initial treatment in the hospital.

What are the implications of the study?

Fondaparinux and enoxaparin have similar safety and efficacy for initial treatment of patients with DVT.