Continuing Medical Education Article Platelet hyperfunction is decreased by additional aspirin loading in patients presenting with myocardial infarction on daily aspirin therapy Ingrid Fuchs, MD; Alexander O. Spiel, MD; Martin Frossard, MD; Ulla Derhaschnig, MD; Eva Riedmu ¨ ller, MD; Bernd Jilma, MD Medical Doctor (IF), Department of Clinical Pharma- cology, Medical University of Vienna, Vienna, Austria; Doctor (AOS), Department of Clinical Pharmacology, Med- ical University of Vienna, Vienna, Austria; Assistant Pro- fessor (MF), Emergency Medicine Department, Medical University of Vienna, Vienna, Austria; Specialist in Internal Medicine (MF), Critical Care Medicine, Medical University of Vienna, Vienna, Austria; Emergency Physician (MF), Medical University of Vienna, Vienna, Austria; Associate Professor for Emergency Medicine (UD), Department of Emergency Medicine, Medical University of Vienna, Vi- enna, Austria; Physician (ER), Department of Emer- gency Medicine, Medical University of Vienna, Vi- enna, Austria; and Associate Professor of Clinical Pharmacology (BJ), Medical University of Vienna, Vienna, Austria. Supported in part by Dade Behring Inc, Deerfield, IL. For information regarding this article, E-mail: bernd.jilma@meduniwien.ac.at Copyright © 2010 by the Society of Critical Care Medicine and Lippincott Williams & Wilkins DOI: 10.1097/CCM.0b013e3181de8b1e LEARNING OBJECTIVES After participating in this activity, the participant should be better able to: 1. Interpret laboratory measures of platelet function. 2. Evaluate effect of aspirin infusion on platelet function. 3. Relate the usefulness of aspirin infusion to individuals with acute coronary syndromes. Unless otherwise noted below, each faculty or staff’s spouse/life partner (if any) has nothing to disclose. The authors have disclosed that they have no financial relationships with, or financial interests in, any commercial companies pertaining to this educational activity. All faculty and staff in a position to control the content of this CME activity have disclosed that they have no financial relationship with, or financial interests in, any commercial companies pertaining to this educational activity. Visit the Critical Care Medicine Web site (www.ccmjournal.org) for information on obtaining continuing medical education credit. 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 al- ready on chronic aspirin therapy. Interventions: Patients received an intravenous infusion of 250 mg aspirin. Measurements and Main Results: Platelet function was mea- sured with a platelet function analyzer in 234 patients before and after aspirin infusion. Aspirin infusion prolonged collagen epineph- rine closure times in almost all patients. Aspirin infusion further lowered thromboxane B2 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-eleva- tion 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. (Crit Care Med 2010; 38:1423–1429) KEY WORDS: randomized controlled trial; aspirin; platelet reac- tivity; acute coronary syndrome 1423 Crit Care Med 2010 Vol. 38, No. 6