Temporal Variability of Platelet Reactivity in Patients Treated with Clopidogrel or Ticagrelor

BACKGROUND AND OBJECTIVES: The degree of antiplatelet response to P2Y12 inhibitors has been associated with clinical outcomes. The aim of this study was to test the variability of platelet reactivity over time among patients treated with clopidogrel or ticagrelor. METHODS: A single-center cohort of acute coronary syndrome patients that underwent percutaneous coronary intervention (PCI) was analyzed. Platelet reactivity was measured at baseline, 48 hours after PCI, 1 month, and 6 months after clopidogrel (n=79) or ticagrelor (n=93) treatment. High on-treatment platelet reactivity (HPR) was defined as ≥47 U, assessed by multiple electrode platelet aggregometry. RESULTS: Platelet reactivity in the clopidogrel group increased over time, 38.2±21.7 U at 48 hours, 41.4±22.3 U at 1 month, and 44.7±25.5 U at 6 months (p=0.018, 48 hours to 6 months). However, platelet reactivity in the ticagrelor group was not significantly changed, 21.4±12.6 U at 48 hours, 20.0±12.2 U at 1 month, and 22.8±13.8 U at 6 months (p=0.392). A platelet reactivity change over time of more than 20U was found in 67.1% of the patients with clopidogrel group and 34.4% of ticagrelor group (p<0.001). Between 48 hours and 6 months, 43% of patients changed their responder status in the clopidogrel group, and 13% in the ticagrelor group (p<0.001). CONCLUSIONS: Although ticagrelor treatment resulted in less temporal variability of platelet reactivity than clopidogrel treatment in terms of HPR, platelet reactivity varied over time in a significant proportion of patients.