title: Effects of tirofiban on haemostatic activation in vitro.
abstract: BACKGROUND
  Thrombin plays a critical role in normal haemostasis and pathological thrombosis. Heparin has long been a mainstay choice of antithrombotic regimen in cardiac patients, but persistent thrombin generation seems to occur during heparin therapy. Because platelets are integral to primary haemostasis and clot formation, we evaluated the use of tirofiban (Aggrastat),a platelet inhibitor, as a therapy to improve heparin sensitivity and delay thrombin formation.
  
  
  METHODS
  Blood samples were obtained from healthy subjects (n=8) and cardiac surgical patients (n=34). Thrombin formation was measured in platelet-rich plasma with a Thrombogram-Ascent fluorescent plate reader system. Platelet inhibition by tirofiban was evaluated with Plateletworks, and the interaction of tirofiban and heparin (>1.5 U ml(-1)) on clot formation was evaluated with Sonoclot Analyzer or kaolin activated clotting times (ACTs).
  
  
  RESULTS
  Addition of tirofiban (70-280 ng ml(-1)) progressively delayed onset of thrombin generation triggered by adenosine diphosphate (ADP). Plateletworks showed platelet inhibition with tirofiban (>35 ng ml(-1)), whereas heparin per se failed to produce platelet inhibition at 7 U ml(-1). Heparin (1.5 U ml(-1)) slowed the onset and rate of fibrin formation on Sonoclot analyses, and this was further slowed after addition of tirofiban (70 ng ml(-1)) to heparin-containing blood samples. Significant increases in ACT at all heparin concentrations were observed with the addition of tirofiban (70 ng ml(-1)). The addition of antithrombin (0.2 units/ml) to heparinized blood samples further prolonged ACTs, but the difference was not statistically significant when compared with heparin alone.
  
  
  CONCLUSIONS
  Tirofiban delays platelet activation-mediated thrombin generation and prolongs ACT in heparinized blood.
authors.affiliation: Department of Anesthesiology, Emory University School of Medicine, Division of Cardiothoracic Anesthesiology and Surgery, Emory Healthcare, Atlanta, Georgia 30322, USA. kenichi_tanaka@emoryhealthcare.org
authors.forename: K A
authors.initials: KA
authors.lastname: Tanaka
authors.forename: N
authors.initials: N
authors.lastname: Katori
authors.forename: F
authors.initials: F
authors.lastname: Szlam
authors.forename: N
authors.initials: N
authors.lastname: Sato
authors.forename: A B
authors.initials: AB
authors.lastname: Kelly
authors.forename: J H
authors.initials: JH
authors.lastname: Levy
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D001777:Blood Coagulation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006487:Hemostasis / Q000187:drug effects*; D006493:Heparin / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D010974:Platelet Aggregation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D013917:Thrombin / Q000096:biosynthesis; D000077466:Tirofiban; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000494:pharmacology*
chemical_list: D010975:Platelet Aggregation Inhibitors; D014443:Tyrosine; D000244:Adenosine Diphosphate; D006493:Heparin; D013917:Thrombin; D000077466:Tirofiban