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DNA Tests to Determine Warfarin Dose
"Everyone we've talked to unanimously was in," said Epstein, who expects the reduction in medical costs will be triple the test price of a few hundred dollars per patient.
He noted a couple dozen companies already are developing commercial tests for variations in the two genes crucial in warfarin dosing, the ones in the new studies. However, sales have been slow for the only government-approved testing device, Roche's Amplichip, which covers numerous gene variations.
  Mayo Clinic technician Paul Heimgartner performs computer analysis of "genetic signatures" to predict how individuals metabolize and respond to the anti-coagulant drug warfarin, which in turn helps doctors find the correct dose for the individual, in Rochester, Minn., Dec. 13, 2006. (AP Photo,Christina Paolucci). (Christina Paolucci - AP) |
A November 2006 report by the American Enterprise Institute-Brookings Joint Center predicts using genetic information to prescribe warfarin would save an estimated $1.1 billion in U.S. health care spending each year, while preventing about 17,000 strokes and 85,000 serious bleeding incidents.
Bleeding complications alone kill about 8,000 people a year and are the No. 2 reason for medication-related ER visits, said Dr. Elizabeth Nabel, director of the National Heart, Lung, and Blood Institute. Still, warfarin is far better at preventing clots than aspirin or drugs like Plavix, which only affect part of the clotting system, she said.
But patients on warfarin must have blood drawn and tested repeatedly to see if it clots too fast or too slow, initially every week or more often.
"Most hospitals have a warfarin clinic, where people come in for adjustments," she noted.
So along with the Food and Drug Administration, her institute now is planning one or two large studies on personalizing warfarin dosing. The FDA also is poised to alter the package insert for warfarin to note that gene variations in some patients mean they need a lower dose than normal.
Meanwhile, five Harvard Medical School teaching hospitals just began a study including 500 warfarin patients to try to boost the percentage getting the optimal dose. Only about 60 percent do now, said Dr. Samuel Goldhaber, a Harvard cardiologist and professor.
At the Marshfield Clinic Research Foundation in Wisconsin, a new study will compare results for 250 patients getting warfarin through standard trial and error with 250 getting doses that are genetically based, said Dr. Michael Caldwell, who started the personalized medicine program there in 2000.
And in the one-year Medco project, DNA from more than 1,000 patients' blood samples will be shipped to the Mayo Clinic, which will do the genetic testing and send the results directly to the patient's doctor. Medco, which manages prescription benefits for one in five Americans, plans to use the results to speed up adoption of the strategy, according to Epstein.
The studies will produce different, but complementary information that can be pooled for a complete picture, Goldhaber said.
Dr. Franklyn Prendergast, director of Mayo's Center for Individualized Medicine, cautioned against assuming the results will be positive, because blood-clotting is a very complicated process.
