title: Prevalence and risk factors for aspirin and clopidogrel resistance in cerebrovascular stenting.
abstract: OBJECTIVE
  The prevalence of antiplatelet drug resistance among patients who undergo cerebrovascular stent placement is unknown. We aimed to assess the feasibility of monitoring antiplatelet drug effects in a single-center cohort undergoing cerebrovascular stent placement.
  
  
  METHODS
  We prospectively collected medical, laboratory, and radiographic data on patients who underwent cerebrovascular stent placement. We used the rapid platelet function assay-aspirin (RPFA-ASA) to calculate aspirin reaction units (ARU) and the P2Y12 assay to calculate P2Y12 reaction units and percentage platelet inhibition. Aspirin resistance was defined as ARU > 550, whereas clopidogrel resistance was defined as percentage platelet inhibition < 40%.
  
  
  RESULTS
  Among 76 patients, stent indications were the following: wide-neck aneurysm (57, 75.0%), symptomatic intracranial stenosis (12, 15.7%), carotid stenosis (5, 6.6%), and vertebral stenosis (2, 2.6%). For aspirin, the median dosage per week was 1300 mg and median ARU was 410. Among 71 patients on aspirin, 3 patients (4.2%) were resistant; there was a significant inverse correlation between aspirin dose and ARU (r = -0.31, P = .01). Among 55 patients on clopidogrel, the median dosage per week was 525 mg with a mean platelet inhibition of 43.2%. Twenty-eight patients (51.9%) were clopidogrel-resistant. In a multivariable linear regression model, age older than 55 years (b = -16.3, P = .020) and diabetes (b = -26.8, P = .015) were inversely related to percentage platelet inhibition.
  
  
  CONCLUSIONS
  Using point-of-care tests, we found that aspirin resistance is relatively uncommon, whereas clopidogrel resistance occurred in half of patients undergoing cerebrovascular stent placement. Further studies should focus on ideal doses, timing, and duration of antiplatelet therapy for cerebrovascular stent placement.
authors.affiliation: Rush University Medical Center, Department of Neurological Sciences, Chicago, IL 60612, USA. Shyam_Prabhakaran@rush.edu
authors.forename: S
authors.initials: S
authors.lastname: Prabhakaran
authors.forename: K R
authors.initials: KR
authors.lastname: Wells
authors.forename: V H
authors.initials: VH
authors.lastname: Lee
authors.forename: C A
authors.initials: CA
authors.lastname: Flaherty
authors.forename: D K
authors.initials: DK
authors.lastname: Lopes
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001241:Aspirin / Q000627:therapeutic use*; D001807:Blood Vessel Prosthesis / Q000706:statistics & numerical data*; D002561:Cerebrovascular Disorders / Q000453:epidemiology* / Q000601:surgery*; D000077144:Clopidogrel; D015331:Cohort Studies; D015897:Comorbidity; D004351:Drug Resistance; D005260:Female; D006083:Graft Occlusion, Vascular / Q000453:epidemiology* / Q000517:prevention & control*; D006801:Humans; D007087:Illinois / Q000453:epidemiology; D015994:Incidence; D008297:Male; D008875:Middle Aged; D010975:Platelet Aggregation Inhibitors / Q000627:therapeutic use; D018570:Risk Assessment / Q000379:methods; D012307:Risk Factors; D015607:Stents / Q000706:statistics & numerical data*; D013988:Ticlopidine / Q000031:analogs & derivatives* / Q000627:therapeutic use
chemical_list: D010975:Platelet Aggregation Inhibitors; D000077144:Clopidogrel; D013988:Ticlopidine; D001241:Aspirin