A 73-year-old woman with a history of atrial fibrillation (AF) presents with a head injury and reduced conscious level. She takes warfarin for her AF and her INR was 2.7 a few days ago. A CT scan of her head is performed which demonstrates the presence of a subdural haematoma.

  1. What is the mechanism of action of warfarin?
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Warfarin acts by inhibiting the vitamin-K dependent synthesis of calcium- dependent clotting factors II, VII, IX, and X (as well as regulatory factors protein C, protein S, and protein Z).

  1. Outline how you will manage her warfarin reversal?
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Her warfarin reversal should be managed as follows:

  • Stop warfarin
  • Administer 5 mg IV vitamin K (phytomenadione)
  • Administer dried prothrombin complex concentrate (factors II, VII, IX and X)
  • Or administer fresh frozen plasma 15 ml/kg if dried prothrombin complex is unavailable
  1. What are the current NICE recommendations for the management of warfarin in the presence of bleeding or an INR outside of the normal range?
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In the presence of major active bleeding, regardless of the INR:

  • Stop warfarin
  • Administer 5 mg IV vitamin K (phytomenadione)
  • Administer dried prothrombin complex concentrate (factors II, VII, IX and X)
  • Or administer fresh frozen plasma 15 ml/kg if dried prothrombin complex is unavailable

 

If the INR is greater than 8.0 with minor bleeding:

  • Stop warfarin
  • Administer 1-3 mg vitamin K (phytomenadione) by slow injection
  • The dose may be repeated after 24 hours if INR remains high
  • Restart warfarin when INR is less than 5.0

 

If the INR is greater than 8.0 with no bleeding:

  • Stop warfarin
  • Administer 1-5 mg vitamin K (phytomenadione) orally
  • The dose may be repeated after 24 hours if INR remains high
  • Restart warfarin when INR is less than 5.0

 

If the INR is 5.0-8.0 with minor bleeding:

  • Stop warfarin
  • Administer 1-3 mg vitamin K (phytomenadione) by slow injection
  • Restart warfarin when INR is less than 5.0

 

If the INR is 5.0-8.0 with no bleeding:

  • Withhold 1 or 2 doses of warfarin
  • Reduce subsequent maintenance dose

 

Further reading:

NICE Clinical Knowledge Summary on the management of warfarin therapy

 

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