title: Evaluation of clopidogrel resistance in ischemic stroke patients.
abstract: OBJECTIVE
  Clopidogrel has potent antiplatelet effects, but recent interest has focused on clopidogrel resistance, in which platelet function is not inhibited despite taking the drug. This study evaluated clopidogrel resistance in ischemic stroke patients.
  
  
  METHODS
  After taking oral clopidogrel 75 mg/day for ≥1 week, platelet aggregometry was performed by turbidimetry in all patients, and by a screen filtration pressure method using whole blood in 37 patients. Using turbidimetry, resistance was defined as platelet maximum aggregation rate ≥34% with aggregation-inducing agent ADP 1 µmol/L, or ≥66% with ADP 4 µmol/L. Using the screen filtration pressure method, resistance was defined as a minimum concentration of ≤3 µmol/L ADP to induce secondary aggregation of platelets.
  
  
  METHODS
  This study was conducted in 72 patients (52 men, 20 women; mean age, 69 ± 8 years; range, 50-84 years) with non-cardiogenic ischemic cerebrovascular disease.
  
  
  RESULTS
  Based on turbidimetry, the rate of clopidogrel resistance was 8.3% with ADP 1 µmol/L and 18.1% with 4 µmol/L. Based on the screen filtration pressure, the rate of clopidogrel resistance was 8.1%. The differences between turbidimetry and screen filtration pressure methods, regarding the measurement of the presence of resistance in the same patient, were observed.
  
  
  CONCLUSIONS
  Clopidogrel resistance varies greatly depending on the method of measuring platelet aggregation and the definition of resistance. Rates of 8-18% were obtained using our methods and criteria.
authors.affiliation: Department of Neurology, Saitama International Medical Center, Saitama Medical University, Japan. tfukuoka@saitama-med.ac.jp
authors.forename: Takuya
authors.initials: T
authors.lastname: Fukuoka
authors.forename: Daisuke
authors.initials: D
authors.lastname: Furuya
authors.forename: Hidetaka
authors.initials: H
authors.lastname: Takeda
authors.forename: Tomohisa
authors.initials: T
authors.lastname: Dembo
authors.forename: Harumitu
authors.initials: H
authors.lastname: Nagoya
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kato
authors.forename: Ichiro
authors.initials: I
authors.lastname: Deguchi
authors.forename: Hajime
authors.initials: H
authors.lastname: Maruyama
authors.forename: Yohsuke
authors.initials: Y
authors.lastname: Horiuchi
authors.forename: Norio
authors.initials: N
authors.lastname: Tanahashi
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000368:Aged; D000369:Aged, 80 and over; D002545:Brain Ischemia / Q000097:blood / Q000188:drug therapy*; D000077144:Clopidogrel; D004351:Drug Resistance; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D009391:Nephelometry and Turbidimetry; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000008:administration & dosage / Q000627:therapeutic use*; D020521:Stroke / Q000097:blood / Q000188:drug therapy*; D013988:Ticlopidine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000627:therapeutic use
chemical_list: D010975:Platelet Aggregation Inhibitors; D000244:Adenosine Diphosphate; D000077144:Clopidogrel; D013988:Ticlopidine