FDA Updates Prescription Guidelines for Blood Thinner

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Lesko noted that genetic tests for the gene variants can cost $125 to $500. The tests may not be readily available in some parts of the United States, he said.

Dr. Janet Woodcock, the FDA's deputy commissioner and chief medical officer, noted during the teleconference that there isn't enough data to make genetic testing a mandate when prescribing warfarin.

"We have to test how good it will be to use genetic information versus the current methods, which are not perfectly satisfactory, but work to initiate warfarin therapy. Then we will have an answer to that question," Woodcock said.

Warfarin is the second most common drug to blame for emergency room visits for adverse drug events, after insulin, the FDA said.

Currently, patients need to have several blood tests over several weeks to determine their optimal warfarin dose.

Patients taking warfarin need to have their blood checked monthly to see if the drug is working properly. The test is called the PT -- or prothrombin time -- test, which evaluates the blood's ability to clot. The results are measured in seconds and compared with the expected value in healthy people.

The changes to the label will be made by manufacturers of warfarin, the generic version of Coumadin. Bristol-Myers Squibb Co., of Princeton, N.J., is the manufacturer of Coumadin, the FDA said.

More information

For more on warfarin, visit the U.S. National Library of Medicine.