Phylloquinone is often called vitamin K1 or phytonadione. It is a fat-soluble vitamin that is stable to air and moisture but decomposes in sunlight. It is found naturally in a wide variety of green plants. Phylloquinone is also an antidote for coumatetralyl. Vitamin K is needed for the posttranslational modification of certain proteins, mostly required for blood coagulation. MEPHYTON (Phytonadione tablets) are indicated in the following coagulation disorders which are due to faulty formation of factors II, VII, IX and X when caused by vitamin K deficiency or interference with vitamin K activity: anticoagulant-induced prothrombin deficiency caused by coumarin or indanedione derivatives; hypoprothrombinemia secondary to antibacterial therapy; hypoprothrombinemia secondary to administration of salicylates; hypoprothrombinemia secondary to obstructive jaundice or biliary fistulas but only if bile salts are administered concurrently, since otherwise the oral vitamin K will not be absorbed. MEPHYTON tablets possess the same type and degree of activity as does naturally-occurring vitamin K, which is necessary for the production via the liver of active prothrombin (factor II), proconvertin (factor VII), plasma thromboplastin component (factor IX), and Stuart factor (factor X). The prothrombin test is sensitive to the levels of three of these four factors II, VII, and X. Vitamin K is an essential cofactor for the gamma-carboxylase enzymes, which catalyze the posttranslational gamma-carboxylation of glutamic acid residues in inactive hepatic precursors of coagulation factors II (prothrombin), VII, IX, and X. Gamma-carboxylation converts these inactive precursors into active coagulation factors, which are secreted by hepatocytes into the blood. Supplementing with Phylloquinone results in a relief of vitamin K deficiency symptoms, which include easy bruisability, epistaxis, gastrointestinal bleeding, menorrhagia and hematuria. Oral phytonadione is adequately absorbed from the gastrointestinal tract only if bile salts are present. After absorption, phytonadione is initially concentrated in the liver, but the concentration declines rapidly. Very little vitamin K accumulates in tissues. Little is known about the metabolic fate of vitamin K. Almost no free unmetabolized vitamin K appears in bile or urine. In normal animals and humans, phytonadione is virtually devoid of pharmacodynamic activity. However, in animals and humans deficient in vitamin K, the pharmacological action of vitamin K is related to its normal physiological function; that is, to promote the hepatic biosynthesis of vitamin K-dependent clotting factors. MEPHYTON tablets generally exert their effect within 6 to 10 hours.