• Includes phytomenadione, phylloquinone, phytonadione, menaquinone.
• Function
  • Activated by epoxide reductase in the liver to the reduced form, which is a cofactor for the γ-carboxylation of glutamic acid residues on various proteins required for blood clotting.
  • K is for Koagulation. Necessary for the maturation of clotting factors II, VII, IX, X, and proteins C and S. Warfarin inhibits vitamin K–dependent synthesis of these factors and proteins.
  • Synthesized by intestinal flora.

• Deficiency
  • Neonatal hemorrhage with ↑ PT and ↑ aPTT but normal bleeding time (neonates have sterile intestines and are unable to synthesize vitamin K). Can also occur after prolonged use of broad-spectrum antibiotics or malabsorption.
  • Not in breast milk; neonates are given vitamin K injection at birth to prevent hemorrhagic disease of the newborn