questions 3

Antiplatelet Drugs

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Topic updated on 09/03/17 4:49pm

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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Qbank (1 Questions)

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(M1.HE.75) A 63-year-old man is aiming to improve his health by eating a well balanced diet, walking daily, and quitting smoking following a 45-year smoking history. While on his daily walks he notices a strong cramping pain in his calves that consistently appears after a mile of walking. He sees his physician and a diagnosis of peripheral artery disease with intermittent claudication is made. To improve his symptoms, cilostazol is prescribed. What is the mechanism of action of this medication? Topic Review Topic

1. Irreversible cyclooxygenase inhibitor
2. Glycoprotein IIB/IIIA inhibitor
3. Thromboxane synthase inhibitor
4. Adenosine diphosphate receptor inhibitor
5. Phosphodiesterase inhibitor

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