Background: Long term outcomes of antiplatelet monotherapy in patients who receive percutaneous coronary intervention (PCI) are unknown. The HOST-EXAM Extended study reports the post-trial follow-up results of the original HOST-EXAM trial. Methods: From March 2014 through May 2018, 5438 patients who maintained dual antiplatelet therapy without clinical events for 12±6 months after PCI with drug-eluting stents (DES) were randomly assigned in a 1:1 ratio to receive clopidogrel 75mg once daily or aspirin 100mg once daily. The primary endpoint (a composite of all-cause death, nonfatal myocardial infarction (MI), stroke, readmission due to acute coronary syndrome (ACS), and BARC type ≥3 bleeding), secondary thrombotic endpoint (cardiac death, non-fatal MI, ischemic stroke, readmission due to ACS, and definite or probable stent thrombosis), bleeding endpoint (BARC type ≥2 bleeding) were analyzed during the extended follow-up period. Analysis was performed on the per-protocol population (2431 patients in the clopidogrel group and 2286 patients in the aspirin group). Results: During median follow-up of 5.8 years (interquartile range, 4.8 and 6.2 years), the primary endpoint occurred in 12.8% and 16.9% in the clopidogrel and aspirin groups, respectively (hazard ratio [HR] 0.74, 95% confidence interval [CI] 0.63 to 0.86, p<0.001). The clopidogrel group had a lower risk for the secondary thrombotic endpoint (7.9% vs. 11.9%; HR 0.66, 95% CI 0.55 to 0.79, p<0.001) and secondary bleeding endpoint (4.5% vs. 6.1%; HR 0.74, 95% CI 0.57 to 0.94, p=0.016). There was no significant difference in the incidence of all-cause death between the two groups (6.2% vs. 6.0%; HR 1.04, 95% CI 0.82 to 1.31, p=0.742). Landmark analysis at 2 years showed that the beneficial effect of clopidogrel was consistent throughout the follow-up period. Conclusions: During an extended follow-up of over 5 years after randomization, clopidogrel monotherapy as compared with aspirin monotherapy was associated with lower rates of the composite net clinical outcome in patients without clinical events for 12±6 months after PCI with DES.

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