title: Aspirin non-responsiveness as measured by PFA-100 in patients with coronary artery disease.
abstract: BACKGROUND
  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).
  
  
  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(R), 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(2) 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 non-responders. A tendency to higher incidence of clinical events among non-responders was observed.
authors.affiliation: Medical Department, Central Hospital of Hedmark, Hamar N-2315, Norway. kjelande@online.no
authors.forename: Kjell
authors.initials: K
authors.lastname: Andersen
authors.forename: Mette
authors.initials: M
authors.lastname: Hurlen
authors.forename: Harald
authors.initials: H
authors.lastname: Arnesen
authors.forename: Ingebjørg
authors.initials: I
authors.lastname: Seljeflot
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000008:administration & dosage / Q000627:therapeutic use; D001241:Aspirin / Q000008:administration & dosage / Q000627:therapeutic use*; D003324:Coronary Artery Disease / Q000097:blood* / Q000188:drug therapy*; D004351:Drug Resistance; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000097:blood / Q000188:drug therapy; D010975:Platelet Aggregation Inhibitors / Q000008:administration & dosage / Q000627:therapeutic use*; D010979:Platelet Function Tests / Q000379:methods*; D014859:Warfarin / Q000008:administration & dosage / Q000627:therapeutic use
chemical_list: D000925:Anticoagulants; D010975:Platelet Aggregation Inhibitors; D014859:Warfarin; D001241:Aspirin