FDA Okays Gene Test to Identify High Risk Warfarin (Coumadin) Patients

ROCKVILLE, Md., Sept. 19 -- The FDA has approved a genetic test to identify patients who have a higher risk of bleeding with warfarin (Coumadin).

The Nanosphere Verigene Warfarin Metabolism Nucleic Acid Test detects variants of two genes, CYP2CP and VKORC1, that affect warfarin metabolism and increase the risk of serious bleeding.

The FDA said the test was not intended as a substitute for other measures of clotting time including comparison to International Normalized Ratio (INR), but should be used along with clinical evaluation and other tools.

Last month the FDA changed the labeling for warfarin to include language explaining that people with variations of the genes CYP2C9 and VKORC1 may respond differently to the drug.

About a third of patients on warfarin metabolize it differently, the FDA release noted, possibly because of those genetic variations.

Daniel Schultz, M.D., director of the FDA's Center for Devices and Radiological Health, said the Nanosphere test is the first FDA-approved genetic test for warfarin sensitivity. The approval, he said, was "another step in our commitment to personalized medicine."

Warfarin, which is a difficult drug to use because optimal dose depends upon a number of factors including patient's diet, age, and use of other drugs, is second only to insulin as a cause of emergency room visits for adverse drug events.

The FDA cleared the test based on results of a study, conducted by the manufacturer, of hundreds of DNA samples as well as on a broad range of published literature. In a three-site study, the test was accurate in all cases where the it yielded a result, but 8% of the tests could not identify which genetic variants were present.