Vitamin K3 (VK3)

Menadione is a polycyclic aromatic ketone, based on 1,4-naphthoquinone, with a 2-methyl substituent. Vitamin K₃ is used in many areas including the pet food industry .

It is sometimes called vitamin K₃, although derivatives of naphthoquinone without the side chain in the 3-position cannot exert all the functions of the K vitamins. Menadione is a vitamin precursor of K₂ which utilizes alkylation to yield menaquinones (MK-n, n=1-13; K₂ vitamers), and hence, is better classified as a provitamin. However, a synthetic form of vitamin K, vitamin K3 (menadione), is demonstrably toxic. In fact, the FDA has banned this synthetic form of the vitamin from over-the-counter supplements because large doses have been shown to cause allergic reactions, hemolytic anemia, and cytotoxicity in liver cells.