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Mode of action
Inhibits vitamin K dependent clotting factors (II, VII, IX, X) as well as the anticoagulant proteins C and S
- If the person has major bleeding, stop warfarin and refer urgently for intravenous treatment with
phytomenadione (vitamin K1), and/or dried prothrombin complex (factors II, VII, IX, and X).
- INR greater than 8.0 with minor bleeding — stop warfarin and arrange same day admission for intravenous phytomenadione. The dose of phytomenadione may be repeated after 24 hours, if the INR is still too high.Restart warfarin when the INR is less than 5.0.
- INR greater than 8.0 and no bleeding — stop warfarin and seek same day specialist advice; intravenous or
oral phytomenadione may be necessary. The dose of phytomenadione may be repeated after 24 hours, if INR still too high. Restart warfarin when INR is less than 5.0.
- INR 5.0 – 8.0 with minor bleeding — stop warfarin; refer urgently for intravenous phytomenadione (1 – 3
mg). Warfarin can be restarted when the INR less than 5.0.
- INR 5.0 – 8.0 and no bleeding — withhold 1 or 2 doses of warfarin and lower the maintenance dose.
- If the INR is high but less than 5 – 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 2 or 3 days later to ensure that it is falling.
Drugs enhance the effect
- Cranberry juice
Drugs that reduce the effect
- Tricyclic antidepressants
- St John’s wort