Abstract 14968: Switching Elderly Patients With High On-treatment Platelet Reactivity From Clopidogrel to Prasugrel

Introduction: In the subgroup of elderly patients (pts) from the TRITON-TIMI 38 (TRial to Assess Improvement in Therapeutic Outcomes by Optimizing Platelet InhibitioN with Prasugrel-Thrombolysis In Myocardial Infarction 38) study, prasugrel 10 mg reduced ischemic events versus clopidogrel 75 mg, but increased bleeding leading to a controversial overall benefit of the prasugrel 10 mg dose in this population. Hypothesis: The study aimed to assess the consequences on platelet inhibition and clinical outcomes of switching elderly pts with high on-treatment platelet reactivity (HTPR) from clopidogrel to prasugrel after an acute coronary syndrome (ACS). Methods: Platelet reactivity was measured at discharge with the VerifyNow P2Y12 assay (Accumetrics, San Diego, California) in 59 elderly ACS pts (age > 75 years) treated with clopidogrel (tailored group). Patients with HTPR were switched from clopidogrel 75 mg to prasugrel 10 mg. The rate of pts with HTPR (P2Y12 reaction units (PRU) > 235, and low on-treatment platelet reactivity (LPR) (PRU Results: On a regimen of clopidogrel 75 mg, the rate of patients with HTPR was 33.9 % (n=20/59), whereas 13.6 % (n=8) had LPR. Among the 33 patients switched to prasugrel, on-treatment platelet reactivity decreased from 287± 35 on a regimen of clopidogrel to 116±71 on a regimen of prasugrel. After switching, the rate of patients with HTPR was 10% whereas the rate of LPR was 41%. In the taylored group, incidence rates (for 100 person-years) of major ischemic events and (major or minor) bleeding events were respectively 26.1 and 39.9 and were not significantly different compared with incidence rates observed in patients from the standard treatment cohort (respectively p=0.59 and p=0.08). Conclusions: HTPR is frequent in elderly patients treated with clopidogrel 75 mg. Early switching from clopidogrel 75 mg to prasugrel 10 mg reduces the number of patients with HTPR but also lead to increase the number of patients with LPR with unknown consequences on clinical outcome.