BACKGROUND: Although aspirin is beneficial in patients with unstable angina, it is a relatively weak inhibitor of platelet aggregation. The effect of Integrelin, which inhibits the platelet fibrinogen receptor glycoprotein (GP) IIb/IIIa, on the frequency and duration of Holter ischemia was evaluated in 227 patients with unstable angina. METHODS AND RESULTS: Patients received intravenous heparin and standard ischemic therapy and were randomized to receive oral aspirin and placebo Integrelin; placebo aspirin and low-dose Integrelin. 45 micrograms/kg bolus followed by a 0.5 microgram.kg-1. min-1 continuous infusion; or placebo aspirin and high-dose Integrelin, 90 micrograms/kg bolus followed by a 1.0-microgram.kg-1, min-1 constant infusion. Study drug was continued for 24 to 72 hours, and Holter monitoring was performed. Patients randomized to high-dose Integrelin experienced 0.24 +/- 0.11 ischemic episodes (mean +/- SEM) on Holter lasting 8.41 +/- 5.29 minutes over 24 hours of study drug infusion. Patients randomized to aspirin experienced a greater number (1.0 +/- 0.33, P < .05) and longer duration (26.2 +/- 9.8 minutes, P = .01) of ischemic episodes than the high-dose Integrelin group. There was no evidence of rebound ischemia after withdrawal of study drug. In 46 patients, platelet aggregation was rapidly inhibited by Integrelin in a dose-dependent fashion. The number of clinical events was small, and there were no bleeding differences in the three treatment arms. CONCLUSIONS: Intravenous Integrelin is well tolerated, is a potent reversible inhibitor of platelet aggregation, and added to full-dose heparin reduces the number and duration of Holter ischemic events in patients with unstable angina compared with aspirin.