Warfarin Complications



  • Most commonly prescribed oral anticoagulant
  • Inhibits vitamin K metabolism required for activation of factors II, VII, IX, and X
  • Blocks the coagulation cascade's extrinsic system and common pathway
  • Commonly used for venous thromboembolism and prevention of embolism with prosthetic heart valves or atrial fibrillation
  • Adjustments based on the international normalization ratio (INR):
    • Typical therapeutic range 2–3
    • 2.5–3.5 for mechanical valves and antiphospholipid syndromes
  • Contraindications include any condition in which the risk of hemorrhage or adverse reaction outweighs clinical benefit:
    • Prior hypersensitivity
    • Skin reactions
    • Recent surgeries
    • Active or potential GI, intracerebral, or genitourinary bleeding
    • Fall risk


  • Bleeding complications:
    • 15% of patients/yr:
      • 4.9% major bleeding events
      • Up to 0.8% fatal, most commonly intracranial hemorrhage (ICH)
    • Bleeding risk is directly related to INR:
      • Increases dramatically above 4
  • Risk factors for nontherapeutic INR:
    • Age >75 yr
    • Hypertension, cerebrovascular disease, severe heart disease
    • Diabetes, renal insufficiency
    • Alcoholism or liver disease
    • Hypermetabolic states, fever
    • Hyperthyroidism
    • Cancer
    • Collagen vascular disease
    • Hereditary warfarin resistance
    • Cytochrome P450 polymorphism

Common Interactions

Increase INRDecrease INR
Multiple antibioticsCarbamazepine
PrednisoneSt. John's wort
CimetidineHigh vitamin K foods
Grapefruit, garlic
Ginkgo biloba

Pregnancy Considerations
  • Pregnancy class X
  • Crosses the placenta causing spontaneous abortion and birth defects

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