title: Local delivery of an antithrombin inhibits platelet-dependent thrombosis.
abstract: BACKGROUND
  Platelet-dependent thrombosis can be effectively inhibited by intravenous administration of direct thrombin antagonists. However, an increased propensity for abnormal bleeding has been associated with systemic administration of these agents. The goal of this study was to determine whether local delivery of a potent thrombin inhibitor, D-Phe-L-Pro-L-Arg chloromethyl ketone (PPACK), could inhibit platelet-dependent thrombosis without altering systemic hemostatic function.
  
  
  RESULTS
  Thrombus formation was measured by quantitative imaging of 111In-labeled platelet deposition on segments of thrombogenic vascular graft interposed in arteriovenous shunts in a porcine model. Intravenous administration of PPACK inhibited platelet deposition at a dose of 12.5 micrograms/kg per minute, which was associated with significant prolongations of both template bleeding times and activated partial thromboplastin times. By contrast, local infusion of PPACK at a dose of 0.02 micrograms/kg per minute (ie, a 600-fold smaller dose) into the fluid boundary layer at the interface between flowing blood and the thrombogenic segment produced equivalent inhibition of platelet deposition without prolonging either the bleeding time or the activated partial thromboplastin time. In addition, static exposure of a mural thrombus to solutions of PPACK at concentrations > or = 2.5 mg/mL for 15 minutes produced sustained inhibition of platelet-dependent thrombosis with no change in hemostatic measurements.
  
  
  CONCLUSIONS
  These results indicate that local delivery of the direct antithrombin PPACK, by either boundary layer infusion or static application techniques, effectively inhibits platelet-dependent thrombosis at doses that are several orders of magnitude less than the systemic dose required for an equivalent antithrombotic effect. In contrast to the systemic administration of PPACK, local delivery produced maximal inhibition of thrombosis without alterations in hemostasis.
authors.affiliation: Division of Cardiology, Emory University Hospital, Atlanta, GA 30322.
authors.forename: N A
authors.initials: NA
authors.lastname: Scott
authors.forename: G L
authors.initials: GL
authors.lastname: Nunes
authors.forename: S B
authors.initials: SB
authors.lastname: King
authors.forename: L A
authors.initials: LA
authors.lastname: Harker
authors.forename: S R
authors.initials: SR
authors.lastname: Hanson
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000008:administration & dosage* / Q000494:pharmacology; D000818:Animals; D000991:Antithrombins / Q000008:administration & dosage* / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology*; D001807:Blood Vessel Prosthesis; D003328:Coronary Thrombosis / Q000517:prevention & control*; D004305:Dose-Response Relationship, Drug; D006487:Hemostasis / Q000187:drug effects; D007275:Injections, Intravenous; D011093:Polyethylene Terephthalates; D013552:Swine
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D000991:Antithrombins; D011093:Polyethylene Terephthalates; C040308:phenylalanyl-prolyl-arginine-chloromethyl ketone