Clopidogrel is increasingly being used for the secondary prevention of ischemic stroke according to the updated guidelines on acute stroke management. Failure to achieve a drug response is referred to as clopidogrel resistance. Similarly, a higher activation of platelets during clopidogrel therapy—high on-treatment platelet reactivity—is equivalent to a reduced effectiveness of a therapy. Clopidogrel resistance is considered to be a common and multifactorial phenomenon that significantly limits the efficacy of antiplatelet agents. The aim of the current study is to review the latest literature data to identify the prevalance and predictors of clopidogrel high on-treatment platelet reactivity among stroke subjects and to establish the potential impact on clinical outcomes and prognosis. Clinical databases were searched by two independent researchers to select relevant papers on the topic, including all types of articles. Several important predictors contributing to clopidogrel resistance were identified, including genetic polymorphisms, the concomitant use of other drugs, or vascular risk factors, in particular nonsmoking and diabetes. Clopidogrel high on-treatment platelet reactivity has a negative impact on the clinical course of stroke, worsens the early- and long-term prognoses, and increases the risk of recurrent vascular events. Platelet function testing should be considered in selected stroke individuals, especially those predisposed to clopidogrel resistance, for whom an improvement in the efficacy of antiplatelet therapy is essential. This particular group may become the greatest beneficiaries of the modification of existing therapy based on platelet function monitoring.
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