All::Cardiovascular System::Pharmacology::Warfarin
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What is the method of action of Warfarin?
- inhibits epoxide reductase preventing the reduction of vitamin K to its active hydroquinone form
- this in turn acts as a cofactor in the carboxylation of clotting factor II, VII, IX and X and protein C.
What is the main clinical use of Warfarin?
- mechanical heart valves
- second-line after DOACs (VTEs, AF etc)
What are the main adverse effects of Warfarin?
- haemorrhage
- teratogenic, although can be used in breastfeeding mothers
- skin necrosis (can temporary cause increased thrombosis risk due to reduced protein C biosynthesis when initiated)
- purple toes
Managing high INR
What's the action required for Major bleeding in a patient on warfarin?
- Stop warfarin
- Give intravenous vitamin K 5mg
- Prothrombin complex concentrate - if not available then FFP*
What's the action required for INR > 8.0 & Minor bleeding in a patient on warfarin?
- Stop warfarin
- Give intravenous vitamin K 1-3mg
- Repeat dose of vitamin K if INR still too high after 24 hours
- Restart warfarin when INR < 5.0
What's the action required for INR > 8.0 & No bleeding in a patient on warfarin?
- Stop warfarin
- Give vitamin K 1-5mg by mouth, using the intravenous preparation orally
- Repeat dose of vitamin K if INR still too high after 24 hours
- Restart when INR < 5.0
What's the action required for INR 5.0-8.0 & Minor bleeding in a patient on warfarin?
- Stop warfarin
- Give intravenous vitamin K 1-3mg
- Restart when INR < 5.0
What's the action required for INR 5.0-8.0 & No bleeding in a patient on warfarin?
- Withhold 1 or 2 doses of warfarin
- Reduce subsequent maintenance dose