Note aspirin is included under COX inhibitors.

Classification of Antiplatelet Agents

Antiplatelet agents can be classified by which stage of platelet function they affect:

  • Adhesion
    • vWF inhibitors
      e.g. Dextran 70.
  • Activation
    • Prostacyclins
      e.g. Epoprostenol.
    • Phosphodiesterase inhibition
      e.g. Dipyridamole.
    • COX inhibitors
      Prevent thromboxane A2 production, e.g. aspirin.
  • Aggregation
    • ADP receptor antagonists
      Prevent activation of GP IIb/IIIa receptors, e.g. clopidogrel.
    • GP IIb/IIIa receptor antagonists
      Prevent platelet aggregation via fibrin linkages between GP IIb/IIIa receptors, e.g. tirofiban.

Comparison of Common Antiplatelet Agents

Property Clopidogrel Dipyridamole Tirofiban
Class ADP antagonist Phosphodiesterase inhibitor GP IIb/IIa antagonists
Uses PVD, STEMI, NSTEMI, stent prophylaxis CVA UA, NSTEMI
Route of Administration PO only PO/IV IV only
Mechanism of Action Irreversibly prevents ADP from binding to its receptor on the platelet, preventing activation of the IIb/IIIa receptor Inhibits platelet adhesion to walls, potentiates prostacyclin activity and increases platelet cAMP, ↓ Ca2+ and inhibiting platelet aggregation and deformation. Also acts as a coronary vasodilator. Reversible antagonism of IIb/IIIa receptor, preventing platelet aggregation
Dosing 300mg load, 75mg daily thereafter 200mg BD for CVA Load 25, maintenance
Absorption Rapid absorption and onset within 2 hours Variable depending on oral intake IV only. Onset within 10 minutes
Distribution Highly protein-bound drug and metabolites Highly protein bound 65% protein bound
Metabolism Prodrug. Majority hydrolysed by esterases to inactive drug, with a small proportion hepatically metabolised by CYP450 to active form. Prolonged duration of action due to irreversible ADP blockade rather than long elimination half-life. Partial hepatic to inactive metabolites Not metabolised.
Elimination Urinary and faecal Renal and faecal Urinary as unchanged drug. Platelet aggregation returns to baseline within 4-8 hours
CVS Vasodilatation may drop CPP in AS and recent MI Coronary artery dissection
GIT Mucosal irritation
Haeme Haemorrhage Thrombocytopaenia and haemorrhage Haemorrhage
Other Many pharmacokinetic interactions, including genetic variability. Previously thought to kinetically interact with omeprazole - more recently disproved.


  1. Peck TE, Hill SA. Pharmacology for Anaesthesia and Intensive Care. 4th Ed. Cambridge University Press. 2014.
  2. Rang HP, Dale MM, Ritter JM, Flower RJ. Rang and Dale's Pharmacology. 6th Ed. Churchill Livingstone.
Last updated 2019-07-18

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