title: Prevalence of ex vivo high on-treatment platelet reactivity on antiplatelet therapy after transient ischemic attack or ischemic stroke on the PFA-100(®) and VerifyNow(®).
abstract: BACKGROUND
  The prevalence of ex vivo high on-treatment platelet reactivity (HTPR) to commonly prescribed antiplatelet regimens after transient ischemic attack (TIA) or ischemic stroke is uncertain.
  
  
  METHODS
  Platelet function inhibition was simultaneously assessed with modified light transmission aggregometry (VerifyNow; Accumetrics Inc, San Diego, CA) and with a moderately high shear stress platelet function analyzer (PFA-100; Siemens Medical Solutions USA, Inc, Malvern, PA) in a pilot, cross-sectional study of TIA or ischemic stroke patients. Patients were assessed on aspirin-dipyridamole combination therapy (n = 51) or clopidogrel monotherapy (n = 25).
  
  
  RESULTS
  On the VerifyNow, HTPR on aspirin was identified in 4 of 51 patients (8%) on aspirin-dipyridamole combination therapy (≥ 550 aspirin reaction units on the aspirin cartridge). Eleven of 25 (44%) patients had HTPR on clopidogrel (≥ 194 P2Y12 reaction units on the P2Y12 cartridge). On the PFA-100, 21 of 51 patients (41%) on aspirin-dipyridamole combination therapy had HTPR on the collagen-epinephrine (C-EPI) cartridge. Twenty-three of 25 patients (92%) on clopidogrel had HTPR on the collagen-adenosine diphosphate (C-ADP) cartridge. The proportion of patients with antiplatelet HTPR was lower on the VerifyNow than PFA-100 in patients on both regimens (P < .001).
  
  
  CONCLUSIONS
  The prevalence of ex vivo antiplatelet HTPR after TIA or ischemic stroke is markedly influenced by the method used to assess platelet reactivity. The PFA-100 C-ADP cartridge is not sensitive at detecting the antiplatelet effects of clopidogrel ex vivo. Larger prospective studies with the VerifyNow and with the PFA-100 C-EPI and recently released Innovance PFA P2Y cartridges (Siemens Medical Solutions USA, Inc) in addition to newer tests of platelet function are warranted to assess whether platelet function monitoring predicts clinical outcome in ischemic cerebrovascular disease.
authors.affiliation: Department of Neurology, The Adelaide and Meath Hospital, incorporating the National Children's Hospital, Trinity College Dublin, Ireland.
authors.forename: Justin A
authors.initials: JA
authors.lastname: Kinsella
authors.forename: W Oliver
authors.initials: WO
authors.lastname: Tobin
authors.forename: Dermot
authors.initials: D
authors.lastname: Cox
authors.forename: Tara
authors.initials: T
authors.lastname: Coughlan
authors.forename: Ronan
authors.initials: R
authors.lastname: Collins
authors.forename: Desmond
authors.initials: D
authors.lastname: O'Neill
authors.forename: Raymond P
authors.initials: RP
authors.lastname: Murphy
authors.forename: Dominick J H
authors.initials: DJ
authors.lastname: McCabe
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001241:Aspirin / Q000494:pharmacology / Q000627:therapeutic use; D000068342:Aspirin, Dipyridamole Drug Combination; D001792:Blood Platelets / Q000187:drug effects; D002545:Brain Ischemia / Q000188:drug therapy*; D000077144:Clopidogrel; D003430:Cross-Sectional Studies; D004176:Dipyridamole / Q000494:pharmacology / Q000627:therapeutic use; D004338:Drug Combinations; D005260:Female; D006801:Humans; D002546:Ischemic Attack, Transient / Q000188:drug therapy*; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000627:therapeutic use*; D010979:Platelet Function Tests; D020521:Stroke / Q000188:drug therapy*; D013988:Ticlopidine / Q000031:analogs & derivatives / Q000494:pharmacology / Q000627:therapeutic use
chemical_list: D000068342:Aspirin, Dipyridamole Drug Combination; D004338:Drug Combinations; D010975:Platelet Aggregation Inhibitors; D004176:Dipyridamole; D000077144:Clopidogrel; D013988:Ticlopidine; D001241:Aspirin