The U.S. Food and Drug Administration today cleared for marketing a new genetic test that will help physicians assess whether a patient may be especially sensitive to the blood-thinning drug warfarin (Coumadin), which is used to prevent potentially fatal clots in blood vessels.
One-third of patients receiving warfarin metabolize it quite differently than expected and experience a higher risk of bleeding. Research has shown that some of the unexpected response to warfarin depends on variants of two genes, CYP2C9 and VKORC1. The Nanosphere Verigene Warfarin Metabolism Nucleic Acid Test detects some variants of both genes.
"Today's action offers physicians the first FDA cleared genetic test for warfarin sensitivity, which is another step in our commitment to personalized medicine,” said Daniel Schultz, M.D., director, FDA's Center for Devices and Radiological Health. “With this test, physicians may be able to use genetic information along with other clinical information to treat their patients.”
Warfarin can be a difficult drug to use because the optimal dose varies depending on many risk factors, including a patient's diet, age, and the use of other medications. Rapidly achieving the correct dose is important. Patients who receive doses that are higher than needed to correctly thin the blood are at risk of life-threatening bleeding. Those who receive doses that are too low may remain at risk of life-threatening blood clots.
Warfarin is the second most common drug, after insulin, implicated in emergency room visits for adverse drug events.
In August, FDA approved updated labeling for Coumadin, the brand name version of warfarin, explaining that people with variations of the genes CYP2C9 and VKORC1 may respond differently to the drug. Manufacturers of generic warfarin are adding similar information to their products' labeling.