Researchers have identified two genes likely to develop dangerous bleeding in patients after taking the anticoagulant warfarin, according the New England Journal of Medicine Thursday.

Some 2 million Americans take warfarin after a heart attack, stroke or major surgery. Doses must be carefully adjusted to prevent blood clots without causing excessive bleeding, the researcher said.

Ute Schwarz and colleagues at Vanderbilt University School of Medicine in Tennessee started with low doses of the drug for people who had certain variants of VKORC1 and CYP2C9.

They looked at the DNA of 297 patients who had just started taking warfarin and found that two genes already implicated in dangerous responses to warfarin can predict who will have a more immediate reaction.

But Schwarz's team found that variations in a different gene called VKORC1 were key for predicting how people would react to their initial doses of warfarin.

(Xinhua/Agencies March 6, 2008)