5.1 Heparin and Coumarin (Warfarin)

• What is the purpose of anticoagulants in thromboembolic conditions?

  To delay the coagulation process
• Which anticoagulants are most useful clinically?

  Heparin and coumarins
• What is heparin and how is it used clinically?

  • Extracted from animal tissues
  • Administered intravenously
  • Increases blood-clotting time from 6 minutes to 30+ minutes
  • Action lasts about 1.5 to 4 hours
  • Destroyed by heparinase enzyme in blood
• What is the typical dosage of heparin for anticoagulation?

  0.5 to 1 mg/kg of body weight
• How does heparin affect blood-clotting time?

  It increases the time to 30 or more minutes
• What happens to heparin's action after injection?

  It occurs instantaneously
• What are the effects of coumarins like warfarin on coagulation factors?

  • Decrease active prothrombin and Factors VII, IX, X
  • Inhibit enzyme VKOR c1
  • Reduce active vitamin K availability
  • Result in biologically inactive coagulation factors
• What enzyme does warfarin inhibit?

  VKOR c1
• What is the consequence of inhibiting VKOR c1?

  Decreased active vitamin K in tissues
• How does the decrease in active vitamin K affect coagulation factors?

  They become biologically inactive
• How long does it take for coagulant activity to decrease after warfarin administration?

  About 12 hours to 50 percent
• What is the coagulant activity of blood after 24 hours of warfarin administration?

  About 20 percent of normal
• What happens to coagulation factors after warfarin is administered?

  • Active factors degrade over several days
  • Replaced by inactive factors
  • Coagulation factors continue to be produced
  • Decreased coagulant activity persists
• When does normal coagulation usually return after stopping coumarin therapy?

  1 to 3 days