New way to regulate blood thinner found

Genetic profile used to set dose

A new system for predicting the proper dose of the blood thinner warfarin could help doctors do a better job of preventing dangerous blood clots and serious bleeding, researchers reported yesterday.

Some patients needed more than twice the weekly dose than others did, the study showed, and the new test better predicted who needed more and who needed less.

Correct dosing of warfarin is crucial. The drug, which is sold under brand names including Coumadin, can prevent blood clots. But too high a dose can cause a patient to bleed to death, while too low a dose can cause strokes or heart attacks as clots form.

The international research team led by Dr. Teri Klein of Stanford University in California took clinical and genetic information from 4,043 patients to create a computer model to predict who would need a higher or lower dose.

The new approach, called pharmacogenetics, uses patients' genetic variations to predict their response to drugs.

Writing in the New England Journal of Medicine, the researchers said they tested the new method on 1,009 other people.

They said the computer model more accurately identified patients who required 21 milligrams of warfarin or less per week and those who required 49 milligrams or more per week.

About 30 million prescriptions for the drug are written in the United States each year and repeated testing to assess clotting time is needed to find the right dose.

The safest dose for one person may be 10 times higher than the best dose for someone else.

The National Institutes of Health is about to launch a large-scale test with 1,200 volunteers to see whether the new system works better.