Hematology: Antiplatelet Medication

Definitions

• Antithrombotic Agents: Prevents Thrombosis/Blood Clots
  • Includes Both Antiplatelet & Anticoagulant Drugs
• Antiplatelet Medication: Prevents Platelet Aggregation
  • Not Technically “Anticoagulation”
• Anticoagulant Medication: Inhibits Clotting Factors

Aspirin (ASA)

• Mechanism of Action: Irreversibly Inhibits Cyclooxygenase (COX)
  • Causes Permanent Inhibition of Prostaglandin (PGH2) Synthesis
  • Decreases Synthesis of Thromboxane A2 (TXA2) – Normally Induces Platelet Aggregation & Vasoconstriction
• Other Effects:
  • Nonsteroidal Anti-Inflammatory Drug (NSAID) & Analgesia
  • Anti-Pyretic
• Dose:
  • Low-Dose (Baby Aspirin): 81 mg
  • High-Dose: 325-650 mg
• Complications:
  • Bleeding
  • GI-Bleed – From Upregulation of COX-2
  • Aspirin-Induced Asthma

Thienopyridines

• Drugs:
  • Clopidogrel (Plavix)
  • Ticagrelor (Brilinta)
  • Prasugrel (Effient)
• Mechanism of Action: Inhibits P2Y12 ADP Receptors on Platelets
  • Inhibits IIb/IIIa Complex (Functionally Similar to Glanzmann Thrombocytopenia)
  • Reversibility:
    • Irreversible Inhibition: Clopidogrel & Prasugrel
    • Reversible Inhibition: Ticagrelor

Bleed Treatment While on Antiplatelet Agents

• Effects Last 5-7 Days Due to Irreversible Binding (Platelet Half-Life is 1 Week)
  • *Ticagrelor is Shorter Due to Reversible Binding
• Treatment Options:
  • Desmopressin (DDAVP)
  • Platelet Transfusion
  • *Limited Data to Support & Controversial
• Reversal Agents are Being Produced & Researched