title: Responsiveness to aspirin in patients with unstable angina pectoris by whole blood aggregometry.
abstract: OBJECTIVE
  To evaluate aspirin responsiveness in patients with unstable angina pectoris (UAP) by whole blood aggregometry. Another goal was to differentiate aspirin-resistant patients into pharmacokinetic or pharmacodynamic type.
  
  
  METHODS
  We measured platelet aggregation by determining impedance values in 70 normal volunteers and 104 UAP patients on aspirin (100 mg/day > or = 7 days) in four inducing conditions [1 microg/ml collagen, 2 microg/ml collagen, 5 micromol/l adenosine diphosphate (ADP) and 10 micromol/l ADP]. We calculated a cut-off value based on data from normal volunteers to define aspirin responsiveness in cases. Then, the correlation and agreement between the results in the four conditions was analysed to choose a preferred inducing condition for identification of aspirin resistance. Aliquots from all samples were incubated with 0.1 mmol/l aspirin and measured again for aspirin-resistant classification.
  
  
  RESULTS
  Aspirin resistance was observed in 38 patients (36.5%), 51 patients (49.0%), 67 patients (64.4%) and 67 patients (64.4%), respectively, for 1 microg/ml collagen, 2 microg/ml collagen, 5 micromol/l ADP and 10 micromol/l ADP among 104 patients. Collagen at low concentration was suggested as a preferred agent for detecting aspirin inhibitory effect according to the coefficient of sensitivity. After incubation, only three among 38 aspirin-resistant patients showed normal platelet aggregation and were classified into pharmacodynamic type.
  
  
  CONCLUSIONS
  In the presence of collagen at low concentration (1 microg/ml), the prevalence of aspirin resistance is about 36.5% in UAP patients, and according to a classification specific for resistant patients, most of the aspirin 'resistance' is just because of pharmacokinetic issues.
authors.affiliation: Institute of Cardiovascular Science, Xinqiao Hospital, Third Military Medical University, Chongqing, China.
authors.forename: J B
authors.initials: JB
authors.lastname: Li
authors.forename: H M
authors.initials: HM
authors.lastname: Dong
authors.forename: Z
authors.initials: Z
authors.lastname: Jian
authors.forename: X J
authors.initials: XJ
authors.lastname: Wu
authors.forename: X H
authors.initials: XH
authors.lastname: Zhao
authors.forename: S Y
authors.initials: SY
authors.lastname: Yu
authors.forename: L
authors.initials: L
authors.lastname: Huang
mesh_terms: D000368:Aged; D000789:Angina, Unstable / Q000097:blood / Q000188:drug therapy*; D001241:Aspirin / Q000493:pharmacokinetics* / Q000627:therapeutic use; D004351:Drug Resistance / Q000502:physiology*; D017097:Electric Impedance; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010974:Platelet Aggregation / Q000187:drug effects*; D010975:Platelet Aggregation Inhibitors / Q000493:pharmacokinetics* / Q000627:therapeutic use
chemical_list: D010975:Platelet Aggregation Inhibitors; D001241:Aspirin