Vitamin K Prophylaxis in the Newborn: Indications and Controversies

Vitamin K is an organic exogenous compound required by humans for a vital function in clotting. It is a fat-soluble vitamin that is easily depleted and poorly stored, requiring dietary replenishing given that it cannot be synthesized in sufficient quantities to meet the requirements of humans and higher mammals. Vitamin K actually refers to not one but a group of fat-soluble (lipophilic, hydrophobic) vitamins that share a common methylated naphthoquinone characteristic chemical structure. There are two naturally occurring forms of vitamin K— vitamin K₁ and vitamin K₂ (Figures 1 and 2). Vitamin K₃ is a synthetic water-soluble substance that is chemically similar to natural vitamin K but with limited effectiveness (Figure 3).