In Reply In response to the 1-year primary analysis of the STOPDAPT-2 trial, Dr Tan commented on the appropriateness of the noninferiority margin and the actual timing of aspirin discontinuation in the 1-month DAPT group.1
In the STOPDAPT-2 trial, the relative 50% noninferiority margin on the hazard ratio scale was chosen based on the feasibility of patient enrollment and the margins adopted in previous major trials,2,3 although the margin was larger than those in some other recent trials (20% and 38%).4,5 However, in trials with low expected event rates such as the STOPDAPT-2 trial, the absolute difference in the event rate between the 2 groups would be reasonably small, even with the relative 50% noninferiority margin, if the 1-sided upper 97.5% confidence limit for the event rate in the 1-month DAPT group was within this noninferiority margin. Furthermore, the 1-month DAPT group was actually superior to the 12-month DAPT group, which makes the discussion of the noninferiority margin less clinically important. The actual event rate in the 12-month DAPT group was lower than anticipated, which reduced the statistical power for the noninferiority analysis (77% for the observed event rate of 3.7%). If the noninferiority margin had been defined in absolute terms, the lower event rate would have made the noninferiority margin inappropriately large, leading to difficulty in study interpretation.6 However, we amended the protocol to change the noninferiority margin from an absolute to a relative margin (50% on the hazard ratio scale) to avoid an inappropriately large noninferiority margin in case the actual event rate was lower than anticipated.
Watanabe H, Kimura T. 1 vs 12 Months of Dual Antiplatelet Therapy for Patients After Percutaneous Coronary Intervention—Reply. JAMA. 2019;322(17):1715–1716. doi:https://doi.org/10.1001/jama.2019.14250
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