February 18, 2009

• Lower warfarin dose required in patients with reduced kidney function

• Warfarin associated with higher risk of bleeding in patients with kidney failure

• Findings may help physicians customize warfarin management in patients with reduced kidney function

BIRMINGHAM, Ala. -- UAB (University of Alabama at Birmingham) researchers say patients with reduced kidney function and kidney failure require lower doses of warfarin, a popular blood thinning medication. These patients also may need closer monitoring to avoid serious bleeding complications, according to findings published on-line in advance of the April issue of the Journal of the American Society of Nephrology.

"Patients who require warfarin generally are older and more likely to have lower kidney function," said Nita Limdi, Pharm.D, Ph.D., MSPH, assistant professor of neurology at UAB and the study's lead author. "Forty percent of the 578 patients on warfarin who participated in the study had moderately reduced kidney function, or kidney failure. These patients required significantly lower warfarin dose to achieve the desired blood-thinning effect."

"Patients with reduced kidney function may need to be monitored more closely, to ensure desired blood-thinning effect is maintained," said Michael Allon, M.D. professor of nephrology at UAB and a study co-author. "This indicates that patient's kidney function may need to be considered in managing warfarin."

While warfarin is a very effective blood thinner, bleeding is a serious complication associated with the drug. Limdi says patients with kidney failure were at higher risk of serious bleeding, and as a result, the benefit of warfarin therapy may be different than in patients with normal kidney function.

Limdi says further research will be needed to determine the harm and benefit associated with warfarin therapy in patients with kidney failure.

"Given the lack of data on patients who developed blood clots despite being on warfarin, we hesitate to recommend the use of kidney function in making-decisions on whether to treat or not treat," Limdi said. "Perhaps ongoing and future research efforts evaluating both clotting and bleeding events will enable more balanced clinical decision making in this unique and medically challenging patient population."

The study was funded through grants from the National Heart Lung and Blood Institute and the National Institute of Neurological Disorders and Stroke.