BOSTON (AP) _ For the first time, doctors have proven that long-term treatment with low doses of a standard blood thinner can reduce the risk of dangerous recurring blood clots in the legs and lungs by two-thirds.
The treatment, using the drug warfarin, was so effective that doctors say it should immediately be offered to the hundreds of thousands of people who suffer these clots each year.
``This is a very safe method for the long-term prevention of potentially fatal recurrent blood clots,'' said Dr. Paul Ridker, who directed the study at Boston's Brigham and Women's Hospital.
The federally financed study was stopped early and released Monday. The results will be published in the April 10 issue of the New England Journal of Medicine and were posted on the journal's Web site.
The American Heart Association estimates that each year, about 2 million people suffer a deep vein thrombosis, a clot in a vein deep in the leg. The result is painful swelling that becomes life threatening if the clot floats to the lungs. This complication occurs in about 600,000 people annually, killing 60,000.
More than half of all cases result from surgery or trauma, such as broken bones, and are not likely to recur. However, Ridker estimates that 750,000 people each year have a deep vein thrombosis resulting from more obscure causes, often an inherited tendency to spontaneously form unwanted clots. Almost a third of these people get another clot within eight years.
His study compared low-dose warfarin and dummy pills in people at risk for these recurring clots. It began in 1998 and was scheduled to end in 2005. However, the early results were so dramatically positive that researchers decided it would be unethical to continue giving people placeboes, so the study was stopped in December.
``This disease generally affects younger people, most of whom are otherwise healthy. The issue of how to manage it is a very, very big problem. Anything that reduces the risk is a major advance, and this is one,'' said Dr. Andrew Schafer, head of medicine at the University of Pennsylvania.
Ridker said that treatment with the generic drug, introduced in 1954, costs pennies a day.
The study was initially intended to enroll 750 people with an average follow up of four years, but it was stopped after 508 patients. Repeat clots occurred in 14 people on low-dose warfarin and 37 getting dummy pills. Four people on warfarin died, as did eight in the comparison group.
The major worry was uncontrolled bleeding, especially strokes. However, the only bleeding stroke occurred in someone in the comparison group. Five people taking warfarin and two on placeboes developed bleeding bad enough to require hospitalization, although all recovered.
The biggest drawback of warfarin is the difficulty establishing the right dose. Two people the same size, sex and age may require vastly different amounts of the medicine to achieve the same result. Doctors set the dose by repeatedly testing the drug's effect on patients' blood clotting.