Warfarin

(Best Syndication) Although the Food and Drug Administration (FDA) approved “updated labeling” for the widely used blood-thinning drug, Coumadin (aka warfarin), they stopped short of recommending genetic testing for patients. The blood thinning medicine’s “activity” is affected partially by genetic factors.

The FDA says that the new labeling will highlight “the opportunity for healthcare providers to use genetic tests to improve their initial estimate of what is a reasonable warfarin dose for individual patients.” People with different gene variations respond to the drug differently. The FDA calls the drug “difficult” to use because the “optimal dose varies and depends on many risk factors including a patient's diet, age, and the use of other medications.”

Research published in the New England Journal of Medicine, Nature and other publications have shed some light on the dosing conundrum. The VKORC1 gene explains 25% of the dose variation between patients. Particular mutations make VKORC1 less susceptible to suppression by warfarin. VKORC1 polymorphisms also explain why African Americans are relatively resistant to warfarin, while Asian Americans are more sensitive. CYP2C9 polymorphisms explain another 10%.

It is important for doctors to closely monitor patients for side effects at the beginning of the therapy. “Patients who take a dose larger than they can tolerate are at risk of life-threatening bleeding. Those who receive too low a dose are at risk of equally dangerous blood clots,” the FDA said.

Doctors should order a PT (prothrombin time) test to determine if the drug is working properly. This test will tell doctors how the blood is clotting. The results are measured in seconds and compared with the expected value in healthy people, known as the International Normalized Ratio or INR.

After insulin, Warfarin is the second most common drug used in emergency rooms. The FDA estimates that 2 million persons start taking warfarin in the United States every year to prevent blood clots, heart attacks and stroke.

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By Marsha Quinn
Best Syndication News Writer