title: Aspirin response and failure in cerebral infarction.
abstract: OBJECTIVE
  The purpose of this study was to assess the biological effect of aspirin as measured by the inhibition of platelet aggregation in patients taking aspirin for stroke prevention and in patients with acute stroke.
  
  
  METHODS
  We administered increasing doses of aspirin (325, 650, 975, and 1,300 mg daily) to 113 patients for stroke prevention and measured the inhibition of platelet aggregation in these patients and in 33 patients with acute stroke taking aspirin before stroke onset.
  
  
  RESULTS
  Eighty-five patients on < or = 325 and six on > or = 650 mg aspirin had complete inhibition of platelet aggregation. Increase of the dose by 325 mg in nine of the 22 patients with partial inhibition of platelet aggregation produced complete inhibition in five patients at 650 mg and in one at 975 mg. At 1,300 mg, three patients still had only partial inhibition of platelet aggregation (aspirin resistance). Of the 33 inpatients with acute stroke, 24 had platelet aggregation studies done before further administration of aspirin. Of these, 19 had complete inhibition of platelet aggregation and three had partial inhibition, with production of complete inhibition of platelet aggregation at dose escalation; one patient was aspirin-resistant and the other noncompliant.
  
  
  CONCLUSIONS
  How the inhibition of platelet aggregation relates to stroke prevention remains unclear. The ability of aspirin and the dose required to inhibit platelet aggregation may depend upon the individual.
authors.affiliation: Department of Neurology, University of Illinois, Chicago College of Medicine 60612.
authors.forename: C M
authors.initials: CM
authors.lastname: Helgason
authors.forename: K L
authors.initials: KL
authors.lastname: Tortorice
authors.forename: S R
authors.initials: SR
authors.lastname: Winkler
authors.forename: D W
authors.initials: DW
authors.lastname: Penney
authors.forename: J J
authors.initials: JJ
authors.lastname: Schuler
authors.forename: T J
authors.initials: TJ
authors.lastname: McClelland
authors.forename: L D
authors.initials: LD
authors.lastname: Brace
mesh_terms: D000368:Aged; D001241:Aspirin / Q000627:therapeutic use*; D002561:Cerebrovascular Disorders / Q000517:prevention & control*; D004305:Dose-Response Relationship, Drug; D004341:Drug Evaluation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010974:Platelet Aggregation / Q000187:drug effects*
chemical_list: D001241:Aspirin