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Aspirin (ASA)
  • Mechanism
    • acetylates and irreversibly inhibits cyclooxygenase in platelets
      • both COX-1 (more important) and COX-2
      • prevents conversion of arachidonic acid to thromboxane A2 (normally secreted by active platelets)
      • decreases platelet activation
    • ↑ bleeding time
    • PT and PTT unchanged
  • Clinical use
    • prevent MI
    • prophylaxis against clotting in atrial arrhythmias and stroke
    • analgesic
    • antipyretic
    • anti-inflammatory
  • Toxicity
    • GI bleeding
    • Reye's syndrome
    • hyperventilation
    • tinnitus
      • affects CN VIII
ADP receptor antagonists (thienopyridines)
  • Drugs
    • clopidogrel 
    • ticlopidine
  • Mechanism 
    • blocks ADP-mediated platelet aggregation which decreases Gp IIa/IIIb expression via the P2y12 receptor
      • via irreversible block of ADP receptors
        • activated platelets secrete ADP
    • prevents expression of glycoprotein IIb/IIIa by platelets
      • inhibits binding of fibrinogen and clot formation
  • Clinical use
    • alternative to ASA
      • reduce risk of thrombotic stroke
      • post-stent surgery
      • post-MI
      • acute coronary syndrome
      • unstable angina
  • Toxicity
    • neutropenia (ticlopidine)
IIb/IIIa inhibitors
  • Drugs
    • abciximab
    • eptifibatide
    • tirofiban
  • Mechanism
    • monoclonal antibody antagonizes IIb/IIIa glycoprotein receptor on activated platelets
      • prevents platelet aggregation 
  • Clinical use
    • acute coronary syndromes
    • percutaneous transluminal coronary angioplasty
  • Toxicity
    • bleeding
    • thrombocytopenia
PDE III inhibitors
  • Drugs
    • cilostazol
    • dipyridamole
  • Mechanism
    • phosphodiesterase III inhibitor
      • ↑ cAMP in platelets
        • inhibits aggregation
      • direct arterial vasodilation
  • Clinical use
    • intermittent claudication
    • prevention of stroke and TIA with aspirin
    • angina
  • Toxicity
    • nausea
    • headache
    • GI upset
    • palpitations
    • facial flushing
    • hypotension
 

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