Objective: Currently 162-325 mg aspirin is recommended for the treatment of acute coronary syndrome. We tested the effect of an additional loading dose of 250 mg aspirin at the onset of acute coronary syndrome in patients who were already on chronic therapy with 100 mg aspirin.
Design: This was a prospective trial in patients presenting with symptoms suggestive of acute coronary syndrome that included a randomized, double-blind, placebo-controlled trial subgroup.
Setting: An emergency department in a tertiary care center.
Patients: Consecutive patients with symptoms suggestive of acute coronary syndrome were enrolled, including a cohort already on chronic aspirin therapy.
Interventions: Patients received an intravenous infusion of 250 mg aspirin.
Measurements and main results: Platelet function was measured with a platelet function analyzer in 234 patients before and after aspirin infusion. Aspirin infusion prolonged collagen epinephrine closure times in almost all patients. Aspirin infusion further lowered thromboxane B(2) levels in patients with acute coronary syndrome who were on chronic aspirin therapy before admission. Concomitantly, collagen epinephrine closure times increased by 22% from 223 secs (95% confidence interval, 192-255 secs) before to 273 secs (95% confidence interval, 252-294 secs) after aspirin infusion (p < .01). Eleven patients with ST-elevation myocardial infarction on daily aspirin therapy (53%) displayed platelet hyperfunction (collagen epinephrine closure times <193 secs). Additional aspirin infusion further decreased platelet function in these patients with ST-elevation myocardial infarction (30% prolongation of collagen epinephrine closure times; p < .01), and only two patients with ST-elevation myocardial infarction still displayed platelet hyperfunction (p = .02).
Conclusion: Aspirin loading in the emergency room further reduced thromboxane B(2) levels and further inhibited platelet function in many patients with acute coronary syndrome already on 100 mg aspirin.