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 5-10 mg IV vitamin K (phytomenadione)
  • And/or prothrombin complex concentrate (factors II, VII, IX and X)
  • Or fresh frozen plasma 15 ml/kg
  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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The current NICE recommendations for the management of warfarin in the presence of bleeding or an INR outside of the normal range is as follows:

In the presence of major active bleeding, regardless of the INR:

  • Stop warfarin
  • Administer 5-10 mg IV vitamin K (phytomenadione)
  • And/or prothrombin complex concentrate (factors II, VII, IX and X)
  • Or fresh frozen plasma 15 ml/kg

 

If the INR is greater than 8.0 with no bleeding or minor bleeding:

  • Stop warfarin
  • Administer 0.5-1 mg vitamin K (phytomenadione) by slow injection
  • Or 5 mg oral vitamin K
  • 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 6.0-8.0 with no bleeding or minor bleeding:

  • Reduce dose of warfarin
  • Restart warfarin when INR is less than 5.0

 

If the INR is high, but less than 5.0

  • The warfarin dose will need to be reduced and/or one or two doses may need to be omitted
  • The INR should then be measured in 2 or 3 days to ensure that it is falling
  • A 15% change of dose is expected to result in a change in the INR of 1, and a 10% dose adjustment is expected to result in a 0.7-0.8 change in the INR

 

A NICE CKS on the management of warfarin therapy can be read in full here:
www.cks.nice.org.uk

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