Role of clopidogrel loading dose in patients with ST-segment elevation myocardial infarction undergoing primary angioplasty: results from the HORIZONS-AMI (harmonizing outcomes with revascularization and stents in acute myocardial infarction) trial.

OBJECTIVES: Our aim was to determine whether a 600-mg loading dose of clopidogrel compared with 300 mg results in improved clinical outcomes in patients with ST-segment elevation myocardial infarction (STEMI) undergoing primary percutaneous coronary intervention (PCI).

BACKGROUND: A 600-mg loading dose of clopidogrel compared with 300 mg provides more rapid and potent inhibition of platelet activation.

METHODS: In the HORIZONS-AMI (Harmonizing Outcomes With Revascularization and Stents in Acute Myocardial Infarction) trial, 3,602 patients with STEMI undergoing primary PCI were randomized to bivalirudin (n = 1,800) or unfractionated heparin plus a glycoprotein IIb/IIIa inhibitor (n = 1,802). Randomization was stratified by thienopyridine loading dose, which was determined before random assignment.

RESULTS: Patients in the 600-mg (n = 2,158) compared with the 300-mg (n = 1,153) clopidogrel loading dose group had significantly lower 30-day unadjusted rates of mortality (1.9% vs. 3.1%, p = 0.03), reinfarction (1.3% vs. 2.3%, p = 0.02), and definite or probable stent thrombosis (1.7% vs. 2.8%, p = 0.04), without higher bleeding rates. Compared with unfractionated heparin plus a glycoprotein IIb/IIIa inhibitor, bivalirudin monotherapy resulted in similar reductions in net adverse cardiac event rates within the 300-mg (15.2% vs. 12.3%) and 600-mg (10.4% vs. 7.3%) clopidogrel loading dose subgroups (p(interaction) = 0.41). By multivariable analysis, a 600-mg clopidogrel loading dose was an independent predictor of lower rates of 30-day major adverse cardiac events (hazard ratio: 0.72 [95% confidence interval: 0.53 to 0.98], p = 0.04).

CONCLUSIONS: In patients with STEMI undergoing primary PCI with contemporary anticoagulation regimens, a 600-mg loading dose of clopidogrel may safely reduce 30-day ischemic adverse event rates compared with a 300-mg loading dose. (Harmonizing Outcomes With Revascularization and Stents in Acute Myocardial Infarction [HORIZONS-AMI]; NCT00433966).