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| |  ESC: Aspirin Resistance Common in Patients on Daily Preventive Therapy By Peggy Peck VIENNA, AUSTRIA -- September 4, 2003 -- Results of two studies examining platelet aggregation in patients taking daily Aspirin (acetylsalicylic acid) suggest that resistance to Aspirin is a significant phenomenon that might explain recurrent events among Aspirin users. The findings were reported here on September 1st at the European Society of Cardiology Congress 2003. Robert Gabor Kiss, MD, PhD, National Center Health Services, Budapest, Hungary, said that, 26.9% of the Hungarian population is at risk for Aspirin resistance. Thus, he noted that it is shortsighted to rely upon Aspirin for secondary prevention of cardiovascular events. Likewise, Tina Poulsen, MD, PhD, research fellow, Odense University Hospital, Odense, Denmark, and colleagues reported that analysis of blood samples taken from patients with a suspected diagnosis of myocardial infarction (MI) indicates that Aspirin resistance is present in 36% of MI patients. "Immediately on admission, we took blood samples from all patients who were on Aspirin therapy [150 mg/day] prior to admission," said Dr. Poulsen. Blood samples from 298 patients were analyzed for biochemical evidence of Aspirin activity, through the measurement of platelet aggregation. Although all of the patients were taking Aspirin, Dr. Poulsen's team noted that they could not find any evidence of Aspirin biochemical activity in 36% of the patients with confirmed MI. And in patients who did not have an acute event, 19% had no evidence of Aspirin activity. Dr. Kiss and colleagues also used a blood test to measure platelet aggregation, and found similar results. The team measured platelet reactivity in 2,275 patients -- 2,215 on Aspirin therapy 100 to 325mg/day and 60 on ticlopidine 500 mg -- and compared those results to platelet activity in blood samples taken from 150 MI or stroke survivors who were not on blood-thinning therapy. The patients were recruited at 10 participating centers. Out of 2,215 cardiovascular patients taking Aspirin alone for secondary prevention, 26.9% showed resistance, while 6.7% of 60 ticlopidine patients were resistant, Dr. Kiss said. Although both researchers said they were convinced that Aspirin resistance is real, they said it is too soon to recommend universal testing to determine Aspirin resistance. Moreover, Dr. Poulsen said that even if a patient were determined to have Aspirin resistance by platelet aggregation measures, she "would not stop the Aspirin because we really don't know if other activity of Aspirin -- for example anti-inflammatory activity -- could provide protection."
[Study titles: "Aspirin and ticlopidine resistance in cardiovascular patients. Multicenter database of 2425 patients aimed to standardize laboratory control of antiplatelet therapy". Abstract 2007 and Aspirin resistance in patients with acute myocardial infarction: is it of any clinical importance?. Abstract 2008]
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