May 20 (HealthDay News) -- A combination of aspirin and the anti-clotting drug dipyridamole reduces blockages and extends the useful life of new artery-vein access grafts used for kidney dialysis, new research has found.

When arteriovenous (AV) grafts fail, it is often due to stenosis -- a narrowing of blood vessels -- at the graft site, and subsequent clotting. If the AV graft is blocked, it can't be used for dialysis, and this is a major cause of declining health in dialysis patients, according to background information in a U.S. National Institute of Diabetes and Digestive and Kidney Diseases news release about the study.

In the study from the Dialysis Access Consortium, 649 patients with new AV grafts at 13 sites in the United States were randomly assigned to the combination treatment or placebo. The researchers found that the combination treatment decreased the rate of loss of primary unassisted graft patency (the useful life of a graft before it's blocked for the first time) by 18 percent and the rate of developing significant stenosis by 28 percent.

"Our trial results show that we now have a drug therapy that significantly prolongs the viability of AV grafts. This is an important step forward as we proceed to develop therapies to improve dialysis patients' quality of life," lead author Dr. Bradley S. Dixon, of the University of Iowa College of Medicine in Iowa City, said in the news release.

The study, which was supported by Boehringer Ingelheim Pharmaceuticals, Inc., appears in the May 21 issue of the New England Journal of Medicine.

"This drug combination provides a modest but important new therapy to keep AV grafts in good working order so patients can get the dialysis they need. But clearly, more research is needed to extend the useful life of AV grafts," Dr. Griffin P. Rodgers, director of the U.S. National Institute of Diabetes and Digestive and Kidney Diseases, said in the news release. The institute also supported the study.

Kidney failure affects more than half a million people in the United States, and 70 percent of them are on dialysis, according to background information in the news release.

SOURCE: U.S. National Institute of Diabetes and Digestive and Kidney Diseases, news release, May 20, 2009