title: Thrombotic thrombocytopenic purpura associated with clopidogrel.
abstract: BACKGROUND
  The antiplatelet drug clopidogrel is a new thienopyridine derivative whose mechanism of action and chemical structure are similar to those of ticlopidine. The estimated incidence of ticlopidine-associated thrombotic thrombocytopenic purpura is 1 per 1600 to 5000 patients treated, whereas no clopidogrel-associated cases were observed among 20,000 closely monitored patients treated in phase 3 clinical trials and cohort studies. Because of the association between ticlopidine use and thrombotic thrombocytopenic purpura and other adverse effects, clopidogrel has largely replaced ticlopidine in clinical practice. More than 3 million patients have received clopidogrel. We report the clinical and laboratory findings in 11 patients in whom thrombotic thrombocytopenic purpura developed during or soon after treatment with clopidogrel.
  
  
  METHODS
  The 11 patients were identified by active surveillance by the medical directors of blood banks (3 patients), hematologists (6), and the manufacturer of clopidogrel (2).
  
  
  RESULTS
  Ten of the 11 patients received clopidogrel for 14 days or less before the onset of thrombotic thrombocytopenic purpura. Although 10 of the 11 patients had a response to plasma exchange, 2 required 20 or more exchanges before clinical improvement occurred, and 2 had relapses while not receiving clopidogrel. One patient died despite undergoing plasma exchange soon after diagnosis.
  
  
  CONCLUSIONS
  Thrombotic thrombocytopenic purpura can occur after the initiation of clopidogrel therapy, often within the first two weeks of treatment. Physicians should be aware of the possibility of this syndrome when initiating clopidogrel treatment.
authors.affiliation: Veterans Affairs Chicago Healthcare System, Department of Medicine, the Robert H. Lurie Comprehensive Cancer Center, Northwestern University, IL 60611, USA. cbenne@nwu.edu
authors.forename: C L
authors.initials: CL
authors.lastname: Bennett
authors.forename: J M
authors.initials: JM
authors.lastname: Connors
authors.forename: J M
authors.initials: JM
authors.lastname: Carwile
authors.forename: J L
authors.initials: JL
authors.lastname: Moake
authors.forename: W R
authors.initials: WR
authors.lastname: Bell
authors.forename: S R
authors.initials: SR
authors.lastname: Tarantolo
authors.forename: L J
authors.initials: LJ
authors.lastname: McCarthy
authors.forename: R
authors.initials: R
authors.lastname: Sarode
authors.forename: A J
authors.initials: AJ
authors.lastname: Hatfield
authors.forename: M D
authors.initials: MD
authors.lastname: Feldman
authors.forename: C J
authors.initials: CJ
authors.lastname: Davidson
authors.forename: H M
authors.initials: HM
authors.lastname: Tsai
mesh_terms: D000328:Adult; D000368:Aged; D000077144:Clopidogrel; D017809:Fatal Outcome; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010951:Plasma Exchange; D010975:Platelet Aggregation Inhibitors / Q000009:adverse effects*; D011697:Purpura, Thrombotic Thrombocytopenic / Q000097:blood / Q000139:chemically induced* / Q000628:therapy; D012008:Recurrence; D013988:Ticlopidine / Q000009:adverse effects / Q000031:analogs & derivatives*
chemical_list: D010975:Platelet Aggregation Inhibitors; D000077144:Clopidogrel; D013988:Ticlopidine