FRIDAY, Aug. 17 (HealthDay News) -- The U.S. Food and Drug Administration has approved new labeling for warfarin and the brand-name version of the drug, Coumadin, that explain how a patient's genetic makeup may affect their reaction to treatment. Patients with certain variants of the CYP2C9 and VKORC1 genes can have an unexpected response to the initial dose.
Warfarin is prescribed to 2 million people a year and it is the second-most common cause of adverse drug reaction-associated hospital admissions in the United States, after insulin.
Because of genetic variations, one-third of patients on warfarin do not metabolize the drug as expected. The consequences for those who take a dose higher than they can tolerate can include life-threatening bleeding, while those taking too low a dose run the risk of dangerous blood clots. Genetic testing prior to beginning treatment enables health care providers to provide a better initial estimate of the optimum dose for a patient.
"Although genetic testing can currently identify who has these genetic variants, more studies are needed to explore the precise starting dose for these patients," said Larry Lesko, Ph.D., director of the FDA's Office of Clinical Pharmacology, in a statement. "FDA has been working with other government agencies and organizations to develop such studies under the auspices of our three-year-old Critical Path Initiative, which addresses the challenges of moving promising medical products from discovery to patient use."
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