The availability of vitamin K is affected by a variety of dietary and drug-related factors.
Vitamin K is fat-soluble and light sensitive (which may reduce levels in unshielded TPN solutions).
Factors interfering with vitamin K absorption:
(1) pica
(2) ingestion of mineral oil
(3) cholestyramine
(4) large oral doses of vitamin A
Factors interfering with enteric production of vitamin K by bacteria:
(1) antibiotics
Factors interfering with vitamin K metabolism (antagonists):
(1) therapy with coumarin/warfarin
(2) coumarin-like compounds in herbal medications or plants
(3) aspirin in large doses
(4) phenytoin
(5) large doses of vitamin E
