Thrombotic thrombocytopenic purpura (TTP): TTP has been reported rarely following use of clopidogrel, sometimes after a short exposure (<2 weeks). TTP is a serious potentially fatal condition and requires urgent referral to a hematologist for prompt treatment. It is characterized by thrombocytopenia, microangiopathic hemolytic anemia (schistocytes [fragmented RBCs] seen on peripheral blood smear), neurological findings, renal dysfunction, and fever. TTP was not seen during clopidogrel's clinical trials, which included over 17,500 clopidogrel-treated patients. In worldwide post marketing experience, however, TTP has been reported at a rate of about four cases per million patients exposed, or about 11 cases per million patient-years. The background rate is thought to be about four cases per million person-years (See Adverse Reactions).
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