Aspirin non-responsiveness as measured by PFA-100 in patients with coronary artery disease

Introduction: The purpose of the present study was to study the concept of aspirin resistance or non-responsiveness by investigating the response to long-term aspirin therapy in patients with a former acute myocardial infarction (AMI). Materials and methods: Patients with an AMI (n = 202) randomly assigned to aspirin 160 mg/day (n = 71), aspirin 75 mg/day and warfarin (INR 2.0-2.5) (n = 58) or warfarin (INR 2.8-4.2) (n=73) were evaluated by the PFA-100, biochemical variables and clinical events after a mean treatment period of 4 years. Results: The limit for being an aspirin non-responder was defined as the 95th percentile value in the warfarin alone group (196 s) with the epinephrine cartridge. In patients on aspirin alone 25/71 (35%) were non-responders and on the combination 23/58 (40%). With the adenosine diphosphate (ADP) cartridge only minor differences were found. The levels of thromboxane B, in both aspirin groups, in responders as well as in non-responders, were extremely low compared to the warfarin alone group. Evaluating both aspirin groups together (n = 129), the levels of soluble P-selectin were significantly higher in non-responders as compared to responders (p = 0.012). During the observation period of 4 years with limited number of events, there was a tendency for higher event rates in non-responders as compared to responders (36% vs. 24%, p = 0.28). Conclusions: In our evaluation of the PFA-100 R a considerable number of post-AMI patients seemed to be non-responders to long-term aspirin therapy in doses of 75 and 160 mg/day. Circulating levels of P-selectin were higher in the nonresponders. A tendency to higher incidence of clinical events among non-responders was observed. (C) 2003 Elsevier Science Ltd. All rights reserved.