Greater inhibitory effects of bivalirudin compared with unfractionated heparin plus eptifibitide on thrombin-induced platelet activation.
OBJECTIVE
The effects of antithrombotic agents on the activation of platelets by thrombin were determined in blood from patients (n=12) with symptomatic coronary artery disease.


METHODS
Blood obtained immediately before cardiac catheterization was incubated in vitro with therapeutic concentrations of unfractionated heparin (1.2 and 2.0 U/ml) alone and in combination with eptifibatide (unfractionated heparin 1.2 U/ml+eptifibatide, 1.7 microg/ml) or bivalirudin (8 and 14 microg/ml). An activated clotting time was determined. Platelet activation was induced with thrombin (0, 5, 15, and 40 U/ml) and assessed with the use of flow cytometry. Fibrin polymerization was prevented by the peptide Gly-Pro-Arg-Pro. The activation of glycoprotein IIb-IIIa and surface expression of P-selectin were identified with antibodies (PAC-1 and anti-CD62).


RESULTS
The activated clotting time was 258+/-13 s with 1.2 U/ml unfractionated heparin alone, 396+/-8 s with unfractionated heparin+eptifibatide, and 348+/-9 s with 8 microg/ml bivalirudin. The binding of PAC-1 (reflecting the potential to aggregate) was decreased most effectively by bivalirudin (percentage of platelets binding PAC-1 in response to 15 U/ml thrombin-unfractionated heparin=54+/-7%, unfractionated heparin+eptifibatide=12+/-4%, bivalirudin=1+/-0.3% of platelets, P<0.05 for bivalirudin compared with unfractionated heparin or unfractionated heparin+eptifibatide and unfractionated heparin+eptifibatide compared with unfractionated heparin). Bivalirudin prevented thrombin-induced surface expression of P-selectin more effectively than unfractionated heparin alone or unfractionated heparin+eptifibatide (percentage of platelets expressing P-selectin in response to 15 U/ml thrombin-unfractionated heparin alone=74+/-5%, unfractionated heparin+eptifibatide=53+/-7%, bivalirudin=1+/-0.3%, P<0.05 for bivalirudin compared with unfractionated heparin or unfractionated heparin+eptifibatide).


CONCLUSIONS
Comparison between pharmacologic concentrations shown to be therapeutic demonstrated that bivalirudin inhibited thrombin-induced activation of platelets to a greater extent than unfractionated heparin alone or in combination with eptifibatide.
Schneider
David J
DJ
Department of Medicine, Cardiology Unit and Cardiovascular Research Institute, University of Vermont, Burlington, Vermont, USA. david.schneider@uvm.edu
Keating
Friederike
F
Sobel
Burton E
BE
D004359:Drug Therapy, Combination; D000077542:Eptifibatide; D005343:Fibrinolytic Agents / Q000494:pharmacology*; D005434:Flow Cytometry; D006493:Heparin / Q000494:pharmacology*; D006629:Hirudins / Q000494:pharmacology*; D066298:In Vitro Techniques; D010446:Peptide Fragments / Q000494:pharmacology*; D010455:Peptides / Q000494:pharmacology*; D015539:Platelet Activation / Q000187:drug effects*; D011994:Recombinant Proteins / Q000494:pharmacology; D013917:Thrombin / Q000187:drug effects*; D014914:Whole Blood Coagulation Time
D005343:Fibrinolytic Agents; D006629:Hirudins; D010446:Peptide Fragments; D010455:Peptides; D011994:Recombinant Proteins; D006493:Heparin; D013917:Thrombin; D000077542:Eptifibatide; C074619:bivalirudin