THE PRESENT REPORT concerns the nature and functions of natural vitamin K compounds and of some synthetic naphthoquinone derivatives, referred to as vitamin K analogues. The report emphasizes the use of these compounds in pediatrics, especially for prevention and treatment of hemorrhagic disease of the newborn. The demonstration that water-soluble analogues of vitamin K may be toxic for the newborn infant makes it imperative that these substances be used judiciously.
FUNCTIONS AND REQUIREMENT OF VITAMIN K
Table I provides information concerning characteristics, sources, available preparations and routes of administration of natural and synthetic compounds with vitamin K activity.
Vitamin K is required for synthesis of prothrombin and proconvertin (stable factor, factor VII), and it probably is involved also in synthesis of Stuart-Prower factor (factor X) and PTC (plasma thromboplastic factor, factor IX) since clotting defects due to deficiencies of these factors as well as to deficiencies of prothrombin and proconvertin occur in states of vitamin K deficiency.
Requirement and Usual Source of Supply
Available evidence indicates that vitamin K compounds cannot be synthesized by the animal organism. However, vitamin K1 is widely distributed in nature, being present in greatest concentrations in green leafy vegetables and in somewhat lesser concentrations in seeds, tubers and fruit. Although it has long been believed that bacterial synthesis of vitamin K2 in the intestine is another important source of the vitamin, recent studies with rats indicate that vitamin K2 formed in this manner is unavailable if coprophagy is prevented. Whether bacterial synthesis of vitamin K2 in the human intestine can contribute to satisfying the requirements for this vitamin is not known, and it is therefore uncertain whether suppression of growth of intestinal micro-organisms by prolonged oral administration of antibiotics or sulfonamides is of practical importance.