While the anticoagulant warfarin can be highly effective in preventing strokes and treating venous thromboembolism, doctors have long struggled with finding the best way manage the drug therapy.

Boston University School of Medicine (BUSM) researchers now claim to have figured out the optimal dosing levels to help patients, according to a study published in December online issue of the Journal of Thrombosis and Haemostasis.

The research team analyzed warfarin use in almost 4,000 patients to determine what are the most effective levels of the drug in a patient's system under different circumstances.

"The study suggests that anticoagulation control could be improved considerably by changing the warfarin dose only when the ratio is 1.7 or lower/3.3 or higher," lead author Dr. Adam Rose, an assistant professor of medicine at BUSM, said in a university news release. "In addition to offering warfarin to as many optimal candidates as possible, we also need to optimize warfarin dose management to fully realize the benefits of anticoagulation."

Previous studies have found that doctors often do not prescribe warfarin enough or at less than optimal doses for patients who could most benefit from it. Part of the reason is not enough is known about proper dosing levels, and misuse of warfarin can put patients at a higher risk of stroke, bleeding and other medical complications.

"This lack of evidence regarding optimal management strategies probably contributes to our limited success in maintaining patients within the therapeutic range," said Rose, who is also a core investigator in the Center for Health Quality, Outcomes and Economic Research at Bedford VA Medical Center in Massachusetts. "Previous studies have clearly shown that time spent outside the therapeutic range contributes to more adverse events for patients, such as stroke and gastrointestinal hemorrhage. Therefore, increasing the time in the therapeutic range is of utmost importance."