title: In vitro dose response to different GPIIb/IIIa-antagonists: inter-laboratory comparison of various platelet function tests.
abstract: OBJECTIVE
  The aim of this study was to assess the inter- and intra-laboratory variation of the concentration-response to the GPIIb/IIIa-antagonists abciximab and eptifibatide on platelet aggregometry and to compare results with flow cytometric tests as well as the rapid platelet function analyser (RPFA).
  
  
  METHODS
  In five different laboratory sites, blood from three to five healthy donors was spiked with abciximab or eptifibatide, followed by the assessment of: (1) aggregometry (anticoagulant: sodium citrate 3.18% or hirudin 5 microg/ml); (2) flow cytometry (fibrinogen binding or PAC1-expression), or (3) RPFA. Dose-response curves were established on the basis of a sigmoidal Imax)-model [I=(Imax)*Cg)/(IC50g + Cg)].
  
  
  RESULTS
  For citrated blood, aggregation induced by 20 microM ADP was blocked up to 100% by both GPIIb/IIIa-antagonists, IC50 values varied between 0.11-0.22 microg/ml for eptifibatide and 1.25-2.3 microg/ml for abciximab. I(max) of the response to 5 microg/ml collagen ranged from 46% to 100%, and IC50 values varied between 0.28-0.34 microg/ml for eptifibatide and 2.3-3.8 microg/ml for abciximab. In hirudinized blood, IC50 values for eptifibatide were 1.5- to 3-fold higher than those obtained with citrated plasma. Inhibition of PAC1-expression by abciximab (IC50) 0.84 microg/ml) showed results similar those of the RPFA (approx. 1.0 microg/ml); larger differences between PAC1 and RPFA results were observed for eptifibatide. Based on aggregometry, eptifibatide concentrations for 80% inhibition varied from 0.27 to 0.55 microg/ml, and were considerably less when the RPFA was taken as basis (0.15 or 0.22 microg/ml). A similar pattern was observed for abciximab.
  
  
  CONCLUSIONS
  We found quite a low inter- and intra-laboratory variation in the in vitro pharmacodynamic characterization of GPIIb/IIIa-antagonists by aggregometry, making results of these tests obtained from different laboratories during clinical trials at least comparable. The RPFA exhibits a higher sensitivity to inhibitory GPIIb/IIIa-effects, in keeping with the "real" inhibition of the activated receptor (PAC1) as assessed with more elaborate flow cytometry.
authors.affiliation: Institute of Clinical Pharmacology, University Hospital, Theodor Stern Kai 7, D-60590, Frankfurt am Main, Germany. harder@em.uni-frankfurt.de
authors.forename: S
authors.initials: S
authors.lastname: Harder
authors.forename: U
authors.initials: U
authors.lastname: Klinkhardt
authors.forename: J
authors.initials: J
authors.lastname: Graff
authors.forename: D
authors.initials: D
authors.lastname: Westrup
authors.forename: C M
authors.initials: CM
authors.lastname: Kirchmaier
authors.forename: E
authors.initials: E
authors.lastname: Glusa
authors.forename: M A
authors.initials: MA
authors.lastname: Mascelli
authors.forename: S J
authors.initials: SJ
authors.lastname: Marciniak
authors.forename: A
authors.initials: A
authors.lastname: Just
authors.forename: W
authors.initials: W
authors.lastname: Lösche
authors.forename: H K
authors.initials: HK
authors.lastname: Breddin
mesh_terms: D000077284:Abciximab; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D019411:Clinical Laboratory Techniques / Q000592:standards* / Q000706:statistics & numerical data; D004305:Dose-Response Relationship, Drug; D000077542:Eptifibatide; D005340:Fibrinogen; D005434:Flow Cytometry / Q000379:methods / Q000592:standards; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000494:pharmacology; D008863:Microspheres; D015588:Observer Variation; D010455:Peptides / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects*; D010979:Platelet Function Tests / Q000295:instrumentation / Q000592:standards / Q000706:statistics & numerical data; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000037:antagonists & inhibitors* / Q000276:immunology
chemical_list: D000911:Antibodies, Monoclonal; D007140:Immunoglobulin Fab Fragments; D010455:Peptides; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D005340:Fibrinogen; D000077542:Eptifibatide; D000077284:Abciximab