FRIDAY, Sept. 7 (HealthDay News) -- A new gene-based dosing formula for the anti-clotting drug warfarin should make it easier to prescribe the correct dose of the blood thinner, researchers say.
Up to this point, doctors have had to engage in a trial-and-error process over several weeks that left patients at risk of hemorrhaging from low doses or developing blood clots with too-high doses.
"We already knew these genes affected warfarin dosing, but we didn't know how to use that information clinically," researcher Dr. Brian Gage, medical director of Barnes-Jewish Hospital's Blood Thinner Clinic, said in a prepared statement. "But with this study, we've established a simple way to combine these genetic factors with clinical factors in a dosing algorithm."
Gage and colleagues developed the formula based on study participants who had undergone hip replacement or knee surgery. The study team focused on two genes, VKORC1 and CYP2C9, which are known to affect the way warfarin operates inside the body.
Using the new method, physicians head to a Web-based tool to calculate a patient's initial dosage more accurately.
Writing in the September issue of Blood, Gage and colleagues said the calculated dose will cut down on the number of dose changes patients will need before the amount is correct.
The method follows on the heels of an Aug. 16 requirement by the U.S. Food and Drug Administration that labeling for warfarin include information about the effect of the two genes. The FDA also called for studies to determine the correct dosage for people with each genetic variation. This is the first study to address that request.
Warfarin, sold under the brand name Coumadin, prevents blood clots and reduces the risk of stroke in patients with atrial fibrillation, artificial heart valves, deep venous thrombosis and pulmonary emboli. It is also used to prevent clots in people who recently had certain orthopedic surgeries.
To learn more about blood clots, visit Deep Vein Thrombosis: What You Should Know.
-- Madeline Vann
SOURCE: Washington University School of Medicine, news release, Aug. 30, 2007
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