Comparison between initial and chronic response to clopidogrel therapy after coronary stenting for acute coronary syndrome and influence on clinical outcomes.

BACKGROUND: Studies have addressed the benefit of tailored therapy based on initial response to clopidogrel loading dose. However, the appropriate timing for platelet testing remains uncertain. METHODS: The present study was performed to compare initial clopidogrel response after 600 mg loading dose and 1-month platelet response and their relationship with ischemic and bleedings events. A total of 475 patients with non-ST-segment elevation acute coronary syndrome undergoing percutaneous coronary intervention have been included in the present study. All patients were treated with 600 mg clopidogrel followed by 150 mg daily. Clopidogrel low response was defined by high on-treatment platelet reactivity (HPR) with vasoactive stimulated phosphoprotein >50%, and "hyperresponse," as platelet reactivity index vasoactive stimulated phosphoprotein (PRI VASP) <95th percentile after 600 mg. RESULTS: After 600 mg, 210 patients were identified with HPR (44%), and 23 patients (5%), with hyperresponse (PRI VASP <8%). At 1 month on 150 mg clopidogrel daily, 184 patients (39%) had HPR (39%), 14 patients (3 %) had hyperresponse, and mean PRI VASP was significantly lower (43% ± 19% vs 46% ± 21%, P = .04). At 1 month, among the 210 patients with HPR after 600 mg, 127 (60%) remained, whereas among the 265 patients responders after 600 mg, only 57 (22%) remained with HPR (60% vs 22%, P < .0001). Initial response was significantly associated with risk of stent thrombosis and bleeding complications, whereas 1-month assessment was only linked with bleeding events. CONCLUSION: In conclusion, the present study showed that initial clopidogrel response in patients with acute coronary syndrome is not a reliable predictor of response to maintenance therapy and their values for prediction of clinical outcome are likely to be different.