Medical Dictionary
vitamin K
noun
Medical Definition of VITAMIN K
1
: either of two naturally occurring fat-soluble vitamins that are essential for the clotting of blood because of their role in the production of prothrombin in the liver and that are used in preventing and treating hypoprothrombinemia and hemorrhage: a : a yellow oily naphthoquinone C31H46O2 that is obtained especially from alfalfa or made synthetically and that has a fast, potent, and prolonged biological effect, is effective orally, and is useful especially in treating hypoprothrombinemia induced by anticoagulant drugs—called also phylloquinone, phytonadione, vitamin K1; see mephyton b : a pale yellow crystalline naphthoquinone C41H56O2 that is obtained especially from putrefied fish meal and is synthesized by various bacteria (as in the intestines of humans and higher animals) and that is much more unsaturated than vitamin K1 and slightly less active biologically—called also menaquinone, vitamin K2
2
: any of several synthetic compounds that are closely related chemically to vitamins K1 and K2 but are simpler in structure and that have similar biological activity; especially : menadione
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