9.6.6 Vitamin K

The oral coumarin anticoagulants, warfarin and phenindione, interfere with Vitamin K metabolism in hepatic cells and their effects can be reversed by vitamin K. If anticoagulation with warfarin is to be continued but rapid reversal of over- anticoagulation is needed a small oral dose of 0.5 to 1mg of vitamin K is generally sufficient. Larger doses lead to prolonged resistance to warfarin.

Intravenous injections of vitamin K should be given with caution as anaphylaxis may occur.

Menadiol phosphate
  • Tablets 10mg (£104.10 = 20mg daily)


  • Prevention of vitamin K deficiency in malabsorption syndromes
Phytomenadione (Vitamin K1)
  • Konakion MM® injection 10mg in 1ml (£0.38 = 1ml ampoule)
  • Konakion MM Paediatric® injection 2mg in 0.2ml (£0.94 = 0.2ml ampoule)


  1. May be given by a single intramuscular injection at birth - see local hospital policy
  2. May be used to reverse over-anticoagulation


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