drug interaction(s) of warfarin with antiplatelet agents

Indications

• aspirin & clopidogrel are recommended for patients after acute myocardial infarction (MI), & many patients with acute MI also have indications for warfarin
  • patients with atrial fibrillation*
  • prophylaxis for venous thromboembolism

* addition of aspirin to warfarin may not reduce risk of myocardial infarction in patients with stable coronary artery disease - no data after cororary revascularization

Drug interactions

• combination of warfarin plus antiplatelet agent associated with substantial risk of serious bleeding
• adjusted relative risks for fatal & nonfatal bleeding relative to aspirin alone:
  • 1.23 for warfarin alone
  • 1.33 for clopidogrel alone
  • 1.47 for aspirin plus clopidogrel
  • 1.84 for aspirin plus warfarin
    • ref gives a much higher relative risk (7.3)
  • 3.52 for clopidogrel plus a vitamin K antagonist
  • 4.05 for aspirin plus clopidogrel plus warfarin
    • adjusted number needed to harm is 12.5 (aspirin plus clopidogrel plus warfarin)

More general terms

• drug interaction