FDA To Revise Recommended Dosage for Blood Thinner

FDA on Thursday plans to announce a revised label for the blood thinner warfarin that will recommend a lower initial dose for patients with certain genetic variations in an effort to "promote the use of genetic factors to predict how individuals will react to medicines," the Wall Street Journal reports.

According to the Journal, the revised label for warfarin "shows the advances in personalized medicine" but also has "led to a clash" between FDA and some physicians. The revised label will not recommend that patients undergo genetic tests before physicians prescribe warfarin, but a section labeled "Precautions" will indicate that certain variations in two genes could "increase the need for more frequent ... monitoring" of patients and the "use of lower warfarin doses."

Larry Lesko, director of clinical pharmacology at FDA, said that the agency has "substantial" evidence to support the revised label for warfarin and predicted that the label would improve the safety of the medication, which can cause bleeding in excessive doses.

However, some physicians maintain that genetic "testing hasn't been proved to reduce the risks" of warfarin and have raised concerns that "patients who don't get the tests and run into trouble will sue doctors, citing the drug's label," the Journal reports.

Medicare covers the tests, which cost between $300 and $500, but most private health insurers do not cover them.

Ann Wittkowsky, a professor at the University of Washington, said, "It would be irresponsible and potentially harmful to suggest that testing be used, or even mentioned, in the label" for warfarin. According to the Journal, in the event that "tests for warfarin sensitivity genes become commonplace, it would encourage other efforts to develop genetic tests linked to popular drugs" (Mathews, Wall Street Journal, 8/16).