Antiplatelet effect of aspirin in patients with cerebrovascular disease

Stroke. 2004 Jan;35(1):175-8. doi: 10.1161/01.STR.0000106763.46123.F6. Epub 2003 Dec 11.


Background and purpose: Aspirin is used commonly to prevent ischemic strokes and other vascular events. Although aspirin is considered safe and effective, it has limited efficacy with a relative risk reduction of 20% to 25% for ischemic stroke. We sought to determine if aspirin as currently used is having its desired antiplatelet effects.

Methods: We ascertained patients with cerebrovascular disease who were taking only aspirin as an antiplatelet agent. Platelet function was evaluated using a platelet function analyzer (PFA-100). PFA test results were correlated with aspirin dose, formulation, and basic demographic factors.

Results: We ascertained 129 patients, of whom 32% were taking an enteric-coated aspirin preparation and 32% were taking low-dose (< or =162 mg/d) aspirin. For the entire cohort, 37% of patients had normal PFA-100 results, indicating normal platelet function. For the patients taking low-dose aspirin, 56% had normal PFAs compared with 28% of those taking > or =325 mg/d of aspirin, while 65% of patients taking enteric-coated aspirin had normal PFAs compared with 25% taking an uncoated preparation (P<0.01 for both comparisons). Similar results were obtained if PFA results were analyzed using mean closure times (low-dose aspirin, 183 sec; high-dose aspirin, 233 sec; enteric-coated, 173 sec; uncoated, 235 sec; P<0.01 for comparisons). Older patients and women were less likely to have a therapeutic response to aspirin, independent of aspirin dose or formulation.

Conclusions: A significant proportion of patients taking low-dose aspirin or enteric-coated aspirin have normal platelet function as measured by the PFA-100 test. If these results correlate with clinical events, they have broad implications in determining how aspirin is used and monitored.

Publication types

  • Clinical Trial

MeSH terms

  • Age Factors
  • Aspirin / pharmacology*
  • Aspirin / therapeutic use
  • Blood Platelets / drug effects*
  • Cerebrovascular Disorders / drug therapy*
  • Cohort Studies
  • Dose-Response Relationship, Drug
  • Drug Resistance
  • Female
  • Humans
  • Inpatients
  • Ischemic Attack, Transient / drug therapy
  • Male
  • Middle Aged
  • Odds Ratio
  • Outpatients
  • Platelet Aggregation Inhibitors / pharmacology*
  • Platelet Aggregation Inhibitors / therapeutic use
  • Platelet Function Tests
  • Prospective Studies
  • Stroke / drug therapy
  • Tablets, Enteric-Coated / pharmacology*
  • Tablets, Enteric-Coated / therapeutic use


  • Platelet Aggregation Inhibitors
  • Tablets, Enteric-Coated
  • Aspirin