Vitamin K and Glucose-6-phosphate Dehydrogenase Deficiency: A Perspective

Vitamin K also includes a few synthetic forms.Vitamin K 3 (menadione) is a synthetic form of vitamin K having no substituent at the C3 position.It acts as a provitamin and is water soluble.Due to the high risk of allergic reactions and toxicity like neonatal brain damage secondary to free radical generation, it is not recommended for human use.It is also used as a feed additive for animals.10 Despite being banned by the Food and Drug Administration in the United States, the pharmaceutical formulation of vitamin K 3 (an injection) for human use is still available in some countries including India.11 Vitamin K 4 and K 5 are also synthetic and possess anticancer properties. Vitamin KVitamin K acts as a cofactor for enzymes that activate vitamin-Kdependent proteins involved in important physiological functions involving regulation of blood coagulation, prevention of vascular calcification, bone metabolism and modulation of cells.1,2 It is a fat-soluble vitamin characterized by the presence of a 2-methyl-1, 4-naphthoquinone ring (Fig. 1). 3 Vitamin K 1 (phylloquinone or phytonadione or phytomenadione) and K2 (menaquinone) are two naturally occurring forms.Vitamin K 1 contains a phytyl side chain at the C3 position.It is available in India in both injectables (1 mg/0.5 mL and 10 mg/1 mL vials) and oral formulations (10 mg tablets).Vitamin K 2 (menaquinone-MK) containspolyprenyl side chain at the C3 position.It has several isoforms depending on the length of the side chain, which ranges from 4 to 13.It is denoted as MK-n (n is the number of unsaturated β-isoprenoid units in the chain).4 Menaquinone-4 (MK-4) is the most active isoform and provides protection from osteoporosis to pathologic calcification.Mammals including humans can themselves synthesize some amount of MK-4 from Vitamin K 1 .Vitamin K 2 is also produced in the gastrointestinal tract by the resident bacterial flora, but their bioavailability is low.[5][6][7] Vitamins K 1 and K 2 have different tissue distribution and bioavailability.Vitamin K 1 and MK-4 were present in the plasma for 8-24 hours after administration.Bioavailability is also dependent on vitamin K sources.8 The amount of absorbed Vitamin K 1 from vegetable products is lower than the equivalent dose given as a supplement.