The rate of brain hemorrhages associated with blood thinning drugs quintupled during the 1990s, according to a new study. In people over age 80, the rate increased more than tenfold.

The increase is largely caused by greater use of the drug warfarin, which is commonly prescribed to prevent blood clotting and ischemic stroke, the most common type of stroke caused by interrupted blood flow to the brain.

The use of warfarin increased after studies showed it reduced the risk of stroke caused by blood clots for people with atrial fibrillation, a condition that produces irregular heart rhythm and becomes more common as people age.

"Warfarin is highly effective in preventing ischemic stroke among people with atrial fibrillation," said study author Matthew L. Flaherty, M.D., of the University of Cincinnati. "For many people, the benefits of preventing ischemic stroke continue to outweigh the risk of a hemorrhagic stroke.

For the study, published in the January 9, 2007 issue of Neurology, researchers identified all patients in the greater Cincinnati area hospitalized with a first-time brain hemorrhage during three years: 1988, 1993-94 and 1999. In 1988, the annual rate of intracerebral hemorrhages associated with use of blood thinning drugs was .8 cases per 100,000 people. In 1999, the rate was 4.4 cases per 100,000 people. For people age 80 and older, the rate increased from 2.5 in 1988 to 45.9 in 1999.

"Our findings should not discourage the use of warfarin when it's appropriate," said Dr. Flaherty, "Doctors can use these findings to make sure they are weighing the risks and benefits of warfarin use for their patients. For researchers, these results may stimulate efforts to develop safer alternatives to warfarin and better treatments for people with brain hemorrhages."