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Warfarin Adds No Benefit to Aspirin Therapy After MI

Kate Traynor

Research conducted by the Department of Veterans Affairs (VA) indicates that combination therapy with low-dose aspirin and warfarin does not offer a clinical benefit over standard aspirin therapy after a myocardial infarction.

Known as the Combination Hemotherapy and Mortality Prevention Study, the six-year investigation sought to determine whether treatment with two antithrombotics would yield more benefits for survivors of myocardial infarction than standard therapy with one agent.

The VA researchers found that the frequencies of death, repeat myocardial infarction, and stroke did not markedly differ between the group of patients who received aspirin 81 mg/day and an adjusted dosage of warfarin sodium and those who took aspirin 162 mg/day. But the 2,522 patients who took both aspirin and warfarin were more likely than the 2,537 patients who used aspirin alone to have had a bleeding episode during therapy. The warfarin dosage was adjusted to maintain an International Normalized Ratio of 1.5–2.5.

Study participation was open to men and women who had been screened at any of 78 VA medical centers within 14 days after an acute myocardial infarction and had a life expectancy of at least two years. Patients who were at high risk for bleeding, were hypersensitive to the effects of warfarin, or had been treated with high dosages of aspirin or a nonsteroidal antiinflammatory drug were ineligible for the study. The results of the study appear in the Feb. 5 issue of Circulation.

During the study, which ran from Oct. 20, 1992, through Sept. 30, 1998, about 17 percent of the members of each group died. Thirteen percent of the patients in each group had another myocardial infarction. Some 3 percent of each group had a stroke.

Two percent of the patients in the aspirin-only group and 3.4 percent of the combination therapy group had a major bleeding episode that led to death, hospitalization, or a transfusion. Most of these bleeding episodes involved the gastrointestinal tract. Minor hemorrhaging occurred in 3 percent of the aspirin-only group and 13.8 percent of the patients who took aspirin and warfarin.

According to the study team, adherence to therapy was high during the follow-up period, which lasted at least 2.7 years for half of the patients. Overall, aspirin users adhered to their assigned therapy during 86 percent of the follow-up period, and people in the combination therapy group did so 71 percent of the time.