TUESDAY, Oct. 14 (HealthDay News) -- A new study reports that warfarin, a common treatment for atrial fibrillation, is either not prescribed by U.S. doctors as often as it could be or, when it is, not at optimal therapeutic doses.

More than 2 million people in the United States have atrial fibrillation (AF), making it a very common heart rhythm disorder. Left untreated, it can lead to other heart problems, chronic fatigue, stroke and congestive heart failure. While warfarin can be effective in managing AF, use of the anticoagulant can also cause bleeding.

The new study is based on a review of insurance claims and published in the October issue of HeartRhythm Journal. It found that less than half of almost 117,000 AF and atrial flutter patients between 1999 and 2005 were on warfarin. Of these, only 19 percent regularly had the proper amount in their blood during testing -- a fact that greatly increased the risk of stroke, arterial thromboembolism and intracranial bleeding for those testing outside the normal range.

"It appears that many doctors prescribe warfarin at a lower dose than required, or simply not at all," author Dr. Alexander Walker, of World Health Information Science Consultants in Wellesley, Mass, said in a news release from the journal's publisher. "It is important that we address this problem, because, unfortunately, it is the misuse of warfarin that can put patients at a higher risk of stroke, bleeding and other medical complications," he said.

But while warfarin is "very effective," when used at optimal levels, Walker added, "warfarin can be a difficult drug to manage."

"We will begin to see more and more alternatives to warfarin developed for the treatment of AF," he said.

More information

The U.S. National Library of Medicine has more about warfarin.