Background

• The name "vitamin K" refers to a group of chemically similar fat-soluble compounds called naphthoquinones. Vitamin K1 (phytonadione) is the natural form of vitamin K, which is found in plants and provides the primary source of vitamin K to humans through dietary consumption. Vitamin K2 compounds (menaquinones) are made by bacteria in the human gut and provide a smaller amount of the human vitamin K requirement. Vitamin K1 is commercially manufactured for medicinal use under several brand names (Phylloquinone®, Phytonadione®, AquaMEPHYTON®, Mephyton®, and Konakion®).
• Vitamin K is necessary for normal clotting of blood in humans. Specifically, vitamin K is required for the liver to make factors that are necessary for blood to coagulate (properly clot), including factor II (prothrombin), factor VII (proconvertin), factor IX (thromboplastin component), and factor X (Stuart factor). Other clotting factors that depend on vitamin K are protein C, protein S, and protein Z. Deficiency of vitamin K or disturbances of liver function (for example, severe liver failure) may lead to deficiencies of clotting factors and excess bleeding.
• Vitamin K deficiency is rare. People at risk for developing vitamin K deficiency include those with chronic malnutrition (including those with alcohol dependency) or conditions that limit absorption of dietary vitamins, such as biliary obstruction, celiac disease or sprue, ulcerative colitis, regional enteritis, cystic fibrosis, short bowel syndrome, and intestinal resection (particularly of the terminal ileum, where fat-soluble vitamins are absorbed). In addition, some drugs may reduce vitamin K levels by altering liver function or by killing intestinal flora (normal intestinal bacteria) that make vitamin K (for example, antibiotics, salicylates, antiseizure medications, and some sulfa drugs). Vitamin K is routinely given to newborn infants to prevent bleeding problems related to birth trauma or when surgery is planned.
• Warfarin is a blood-thinning drug that functions by inhibiting vitamin K-dependent clotting factors. Warfarin is prescribed by doctors for people with various conditions, such as atrial fibrillation, artificial heart valves, a history of serious blood clots, clotting disorders (hypercoagulability), and placement of indwelling catheters or ports. Usually, blood tests must be done regularly to evaluate the extent of blood thinning, using a test for prothrombin time (PT) or the international normalized ratio (INR). Vitamin K can decrease the blood-thinning effects of warfarin and will therefore lower the PT or INR value. This may increase the risk of clotting. Therefore, people taking warfarin are usually warned to avoid vitamin K supplements. Conversely, vitamin K is used to treat overdoses or any excess anticoagulant effects of warfarin and to reverse the effects of warfarin prior to surgery or other procedures.

References

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