Study: Longer drug treatment prevents recurrent clots

Web posted March 25, 1999

By Linda A. Johnson
Associated Press

People recovering from dangerous blood clots in their legs need to take clot-preventing drugs for much longer than the standard three months to prevent a recurrence, a study found.

Painful clots in a vein deep inside the leg strike more than 40,000 Americans each year, and at least 15 percent have another such clot, often just months later. Such clots can kill within hours if a large enough piece breaks off, travels to the heart and becomes lodged in a lung vein.

Doctors usually treat patients with such deep-vein clots with blood-thinning intravenous medicine for a week, then have them take an inexpensive clot-preventing pill, warfarin, for three months.

But after that, these patients still run an increased risk of another clot, unless the original one was due to a reversible condition, such as an injury, surgery or immobilization.

Canadian researchers compared the three-month treatment with a longer course and found a 95 percent reduction in the risk of another clot among patients who had been on warfarin for an average of 13 months.

The study was supposed to run for more than two years but was cut short because the extended treatment proved so effective that doctors couldn't justify taking the other patients off warfarin. About 5 percent of recurrent clots are fatal.

The 1994-97 study was led by Dr. Clive Kearon, a professor of medicine at McMaster University in Hamilton, Ontario, and was published in Thursday's New England Journal of Medicine.

Among the 83 patients treated with warfarin for three months and then given dummy pills, 17 had another life-threatening leg clot during the study and three of them died.

Of the 79 people receiving the longer warfarin treatment, one died and one had another clot, although that was after the patient stopped taking warfarin because it had caused serious internal bleeding. Two other patients getting the longer warfarin treatment also suffered major internal bleeding.

That is the biggest risk with warfarin, a 50-year-old drug also known as Coumadin. But generally, a clot is considered a deadlier risk than bleeding.

Dr. Robert W. Hobson II, director of vascular surgery at New Jersey Medical School in Newark, said patients with deep-vein clots now ``should know that if somebody has told them three months on Coumadin is enough, it isn't.'' He generally keeps his patients on the drug for four to six months.

Kearon and other scientists are now doing more studies to determine the ideal dose and duration of treatment.

In an accompanying editorial, Dr. Andrew I. Schafer of Baylor College of Medicine in Houston said this is an important study that should make doctors start treating deep-vein clots ``as a chronic rather than acute disease.''