WESTPORT, CT (Reuters Health) – Fondaparinux, a new synthetic pentasaccharide that selectively inhibits activated factor X, is more effective than enoxaparin in preventing venous thromboembolism after hip and knee surgery, according to the results of two studies conducted by the same research group. Both papers appear in the November 1st issue of The New England Journal of Medicine.

In the first report, lead author Dr. Bengt I. Eriksson from Sahlgrenska University Hospital-?stra, Gצteborg, Sweden, and colleagues randomly assigned 1711 patients undergoing surgery following fracture to the upper third of the femur to subcutaneous fondaparinux 2.5 mg once daily for 5 days, or to 40 mg enoxaparin once daily for 5 days. Fondaparinux was initiated after surgery and enoxaparin was initiated before surgery.

After 11 days, the incidence of venous thromboembolism was 8.3% in the fondaparinux group compared with 19.1% in the enoxaparin group (p < 0.001). Patients who received fondaparinux had a 56.4% reduction in venous thromboembolism risk, the research team reports.

There were no significant differences between the groups in mortality or clinically relevant bleeding, Dr. Eriksson and colleagues note.

In the second study, lead author Dr. Kenneth A. Bauer from Beth Israel Deaconess Medical Center, Boston, and colleagues randomized 1049 patients who underwent elective knee surgery to 2.5 mg fondaparinux once daily or 30 mg enoxaparin twice daily. The patients were treated for up to 9 days, with subcutaneous treatment starting no later than 12 hours after the procedure.

Patients who received fondaparinux had significantly fewer episodes of venous thromboembolism (12.5%) compared with patients who received enoxaparin (27.8%), for a 55.2% risk reduction in the fondaparinux group (p < 0.001), Dr. Bauer's group reports.

Although there were more episodes of major bleeding in the fondaparinux group (p = 0.006), there were no significant differences in bleeding that led to death, reoperation or that affected a critical organ in either group, the investigators note.

For patients undergoing hip or knee surgery, Dr. Bauer's group concludes that fondaparinux is significantly more effective in preventing venous thromboembolism.

"In the operating room, in the intensive care unit, and in patients with renal failure…unfractionated heparin is still the agent of choice, given its short half-life, easy reversibility, and extrarenal metabolism," Dr. David L. Diuguid from the College of Physicians and Surgeons of Columbia University, New York, comments in a journal editorial.

"However, there are clear advantages to the newer agents, and we should use them appropriately, especially in the area of prophylaxis against venous thromboembolism," he adds.

N Engl J Med 2001;345:1298-1310,1340-1341.