FDA: Genetic Test Can Improve Coumadin Dosing
The FDA has approved new labeling for the blood-thinning drug warfarin (Coumadin) to inform people that their genetic makeup may affect how they respond to the drug, according to an August 16, 2007 press release.
Warfarin interferes with the blood's ability to clot, and is used after a heart attack to reduce the risk of dying or having another heart attack or stroke. It may also be used to prevent blood clots in patients with a rapid, irregular heart beat ( atrial fibrillation), mechanical heart valves, or blood clots in the lungs or veins of the lower legs.
According to the FDA, about 2 million people per year start taking warfarin. It's important that each person gets exactly the right dose of the drug: too little, and it won't prevent blood clots; too much, and it can cause dangerous bleeding. Getting the right dose is difficult because each person responds differently. As many as one third of patients respond very differently than expected to warfarin, and it's the second most common cause (after insulin) of emergency room visits because of medication problems.
It is already known that age, diet, body size, high blood pressure, extent of heart disease, and some other medications can affect how a person reacts to warfarin. This latest labeling change reflects the knowledge that a person's genetic makeup also plays a part. People with variations in two specific genes (CYP2C9 and VKORC1) may need to start with lower doses than people without these variations. A genetic test is available that shows what variants a person has, enabling doctors to make a better estimate of the correct dose, meaning patients are less likely to experience dangerous side effects. The FDA stops short of requiring the genetic test for all patients starting warfarin.
Warfarin is one of five drugs for which the FDA has approved adding labels that mention genetic variations. These changes are just the tip of the iceberg: researchers continue to discover more about the roles specific genes play in determining whether or not a person develops heart disease and how he or she responds to treatment. As more becomes known and doctors are able to tailor therapies to an individual's unique medical history and genetic makeup, it's likely that increasing numbers of treatment and drug choices will be influenced by the results of genetic tests.
U.S. Food & Drug Administration. “FDA Approves Updated Warfarin (Coumadin) Prescribing Information.” August 16, 2007. Available at: http://www.fda.gov/cder/drug/infopage/warfarin/qa.htm. Accessed August 21, 2007.
U.S. Food & Drug Administration. “Questions and Answers on New Labeling for Warfarin (marketed as Coumadin).” August 16, 2007. Available at: http://www.fda.gov/cder/drug/infopage/warfarin/qa.htm. Accessed August 21, 2007.