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BACKGROUND: The safety of omitting up-front treatment with aspirin during primary percutaneous coronary intervention (PCI) in patients with ST-segment elevation myocardial infarction (STEMI) remains unclear.

METHODS: We conducted a multicenter, open-label, randomized trial in Japan involving patients with STEMI who were undergoing primary PCI. Patients were randomly assigned in a 1:1 ratio before PCI to receive low-dose prasugrel monotherapy or dual antiplatelet therapy (DAPT) with aspirin and low-dose prasugrel for 12 months. The primary outcome was a composite of death from any cause, stroke, or myocardial infarction at 12 months, which was assessed for noninferiority with a prespecified noninferiority margin of 1.50 for the 95% confidence interval of the hazard ratio. The major secondary outcome was major bleeding (defined as a bleeding event of Bleeding Academic Research Consortium [BARC] type 3 [nonfatal major bleeding] or 5 [fatal bleeding]) at 12 months, which was assessed for superiority if noninferiority was established for the primary outcome.

RESULTS: A total of 2216 patients were included in the full analysis population; 1109 were assigned to receive monotherapy and 1107 to receive DAPT. At 12 months, death from any cause, stroke, or myocardial infarction had occurred in 124 patients (Kaplan-Meier estimate, 11.0%) in the monotherapy group and in 94 patients (Kaplan-Meier estimate, 8.5%) in the DAPT group (hazard ratio, 1.34; 95% confidence interval [CI], 1.02 to 1.75; P = 0.40 for noninferiority). Major bleeding had occurred in 61 patients (Kaplan-Meier estimate, 5.6%) in the monotherapy group and in 92 patients (Kaplan-Meier estimate, 8.4%) in the DAPT group (hazard ratio, 0.66; 95% CI, 0.47 to 0.91). The percentages of patients with definite or probable stent thrombosis and serious adverse events appeared to be similar in the two groups.

CONCLUSIONS: Among patients with STEMI who were undergoing primary PCI, low-dose prasugrel monotherapy initiated before PCI was not noninferior to DAPT for 12 months with respect to a composite of death from any cause, stroke, or myocardial infarction at 12 months. (Funded by Boston Scientific Japan; PREMIUM ClinicalTrials.gov number, NCT05709626.).

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