Early discontinuation of prasugrel or clopidogrel in acute coronary syndromes

BACKGROUND: In the Targeted Platelet Inhibition to Clarify the Optimal Strategy to Medically Manage Acute Coronary Syndromes (TRILOGY ACS) trial of patients with non-ST-segment elevation acute coronary syndrome managed medically without revascularization, treated with prasugrel versus clopidogrel for less than or equal to 30 months after index acute coronary syndrome, post-hoc analyses showed a divergence of treatment effect in favor of prasugrel after 12 months. Potential influential factors, including a potential late treatment effect after early study drug discontinuation in the intention-to-treat analysis, have not been explored. PATIENTS AND METHODS: We carried out an exploratory, post-hoc analysis of 1436 patients who received at least one dose of the study drug and discontinued the drug 7-365 days after randomization. Kaplan-Meier event rates were evaluated starting at the landmark timepoint of study discontinuation through 2 years of follow-up, and were compared between prasugrel and clopidogrel. RESULTS: The unadjusted rates of the primary composite endpoint of cardiovascular death, myocardial infarction, or stroke were 20.1 versus 24.4% in the prasugrel versus clopidogrel groups (log-rank P=0.069). Similar findings were observed for cardiovascular death (13.3 vs. 18.0%, log-rank P=0.022), and cardiovascular death or myocardial infarction (19.3 vs. 23.3%, log-rank P=0.042). In multivariable analyses, there were no significant differences in the adjusted risk of these outcomes between the prasugrel and clopidogrel groups. CONCLUSION: In this hypothesis-generating analysis, high rates of ischemic events were observed after study drug discontinuation, with a lower frequency of events among patients treated with prasugrel versus clopidogrel that did not persist after multivariable adjustment. This analysis highlights the complexities of ascertaining downstream effects of antithrombotic therapies after drug discontinuation.