Vitamin K

Dr Daniel J Bell and Dr Craig Hacking et al.

Vitamin K is a family of fat-soluble vitamins essential for normal blood-clotting function and comprises two vitamers that are found naturally: phytomenadione (also known as phylloquinone or K1) and menaquinone (or K2).

Menadione is a synthetic molecule which is occasionally called vitamin K3 however this is a misnomer as it is not found in nature. It used to be used to treat hypovitaminosis K in neonates but is now banned due to toxicity at higher doses. which is not seen with the naturally-occurring vitamins K1 and K2

Menaquinone is synthesised by normal flora in the intestine although the amount produced in vivo in the human gut is likely negligible. Vitamin K serves as a coenzyme for the clotting factors II, VII, IX and X. Warfarin inhibits vitamin K by preventing its enzymatic reactivation. 

Pathological manifestations are rare.

Hypovitaminosis K can lead to jaundice and anemia in the neonate. 

Hypervitaminosis K is extremely rare but when present may cause thrombophilia or hemolysis 3

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Article information

rID: 49232
Section: Pathology
Synonyms or Alternate Spellings:
  • Vitamin K3
  • Menadione
  • Menaquinone
  • Phylloquinone
  • Phytomenadione
  • Vitamin K2
  • Vitamin K1

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