BACKGROUND: Clopidogrel is commonly used in the prevention and treatment of cardiovascular events. However, despite clopidogrel treatment, some patients experience recurrent ischemic events.

CASE REPORT: We present the case of a 58-year-old man with polycythemia vera and concomitant thrombocytosis who suffered 6 episodes of cerebral infarctions and 1 myocardial infarction, despite treatment with clopidogrel. Following his last ischemic event, the antiplatelet therapy was intensified from initially clopidogrel monotherapy to dual antiplatelet therapy with aspirin 75 mg once daily and ticagrelor 90 mg twice daily. Since then, no cardiovascular event has been reported.

CONCLUSIONS: This case report illustrates that insufficient platelet inhibition with clopidogrel monotherapy in a patient with thrombocytosis may be associated with recurrent arterial thrombosis. The exact reasons for the insufficient platelet inhibition are not known, but a plausible explanation may be an accelerated platelet turnover reflected by an increased number of immature platelets in this patient.

Keywords: Blood Platelets, Platelet Aggregation, Platelet Aggregation Inhibitors, Platelet Count, Purinergic P2Y Receptor Antagonists, Thrombocytosis