Menadione

Menadione is a synthetic chemical compound sometimes used as a nutritional supplement because of its vitamin K activity. It is an analog of 1,4-naphthoquinone with a methyl group in the 2-position.

Terminology
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.

It is also known as "menaphthone".

Uses
Despite the fact that it can serve as a precursor to various types of vitamin K, menadione is generally not used as a nutritional supplement in economically developed countries. Menadione for human use at pharmaceutical strength is available in some countries with large lower income populations. Large doses of menadione have been reported to cause adverse outcomes including hemolytic anemia due to G6PD deficiency, neonatal brain or liver damage, or neonatal death in some rare cases. In the United States, menadione supplements are banned by the U.S. Food and Drug Administration (FDA) because of their potential toxicity.

Low dose menadione is still used as an inexpensive micronutrient for livestock in many countries. Forms of menadione are also included in some pet foods in developed countries as a source of vitamin K.

It is used in the treatment of Hypoprothrombinemia

Experimental research
Menadione has been used experimentally as a chemotherapic agent for cancer since 1947. More recently, menadione in combination with vitamin C is being studied as a potential treatment for prostate cancer.

A menadione topical lotion was recently developed to reduce epidermal growth factor receptor inhibitor related side effects, by the prevention of skin toxicities that result from inhibition of protein kinases by drugs such as erlotinib (Tarceva) and cetuximab (Erbitux).