Almost half of stroke patients may be aspirin resistant

25th Jun 2004

VANCOUVER (Reuters Health) - The results of a small study suggest that almost half of patients hospitalized after a stroke or transient ischemic attack (TIA) that are caused by a blocked blood vessel do not develop anti-clotting effects with aspirin therapy.

Dr. Mark Alberts, of Northwestern University Medical School, Chicago, reported at the 5th World Stroke Congress that 47 percent of stroke or TIA patients showed "aspirin resistance," which was defined as a clotting time of 171 seconds or less.

The study involved 59 patients (average age 64 years) who had been taking aspirin for at least three days before they had a stroke or TIA. The patients were tested at the time of hospital diagnosis, before treatment with additional anticlotting therapy.

The researchers used a machine that measures the clotting time of a blood sample that is pumped through a membrane, a test design that mimics the behavior of circulating blood. The results, Alberts said, are available in "about 5 minutes -- and the test costs only $15 to $20."

Sixty-three percent of patients were taking 325 mg/day of aspirin, and 37 percent were using 81 mg. Aspirin resistance was more common in patients taking low-dose aspirin. The results were normal in 73 percent of patients on the low-dose aspirin versus 32 percent of patients taking high-dose aspirin.

There also was a trend towards more resistance in patients taking enteric-coated aspirin compared with those taking uncoated aspirin (73 percent versus 39 percent).

The results suggest that "dose-adjusted antiplatelet therapy is where the field is heading," Alberts concluded. "One size fits all therapy doesn't work for aspirin."

By M. Mary Conroy.

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