シンカビト

Menadiol sodium diphosphate is a highly water-soluble vitamin K analog. The presence of vitamin K is necessary for the formation of prothrombin, factor VII, factor IX and factor X. Lack of vitamin K results in an increased risk of hemorrhage, which can be minor or life-threatening.

Menadiol sodium phosphate (vitamin K3) is involved as a cofactor in the posttranslational gamma-carboxylation of glutamic acid residues of various proteins in the body, allowing for propagation of the clotting cascade that results in coagulation. These proteins are comprised of the vitamin K-dependent coagulation factors II (prothrombin), VII (proconvertin), IX (Christmas factor), X (Stuart factor), protein C, protein S, protein Zv and a growth-arrest-specific factor (Gas6). The two vitamin K-dependent proteins found in bone are osteocalcin, also known as bone G1a (gamma-carboxyglutamate) protein or BGP, and the matrix G1a protein or MGP. Gamma-carboxylation is catalyzed by the vitamin K-dependent gamma-carboxylases. The reduced form of vitamin K, vitamin K hydroquinone, is the actual cofactor for the gamma-carboxylases. Proteins containing gamma-carboxyglutamate are called G1a proteins.

Menadione or 2-methyl-1,4-naphthoquinone is a synthetic vitamin K analog, undergoes 1-electron reduction by enzymes such as microsomal NADPH–cytochrome P450 reductase and mitochondrial NADH–ubiquinone oxidoreductase (complex I), resulting in redox cycling, or it detoxification via two-electron reduction by NAD(P)H–quinone oxidoreductase. Vitamin K is a group of lipophilic, hydrophobic vitamins that exist naturally in two forms (and in 3 synthetic forms): vitamin K1, which is found in plants, and vitamin K2, which is synthesized by bacteria. Vitamin K is an important dietary component because it is necessary as a cofactor in the activation of vitamin K dependent proteins. Metabolism of vitamin K occurs mainly in the liver. In the first step, vitamin K is reduced to its quinone form by a quinone reductase such as NADPH dehydrogenase. Reduced vitamin K is the form required to convert vitamin K dependent protein precursors to their active states. It acts as a cofactor to the integral membrane enzyme vitamin K-dependent gamma-carboxylase (along with water and carbon dioxide as co-substrates), which carboxylates glutamyl residues to gamma-carboxy-glutamic acid residues on certain proteins, activating them. Each converted glutamyl residue produces a molecule of vitamin K epoxide, and certain proteins may have more than one residue requiring carboxylation. To end the cycle, the vitamin K epoxide is returned to vitamin K via the vitamin K epoxide reductase enzyme, also an integral membrane protein. The vitamin K dependent proteins include various important coagulation factors, such as prothrombin. Warfarin and other coumarin drugs act as anticoagulants by blocking vitamin K epoxide reductase.

Menadiol sodium phosphate (vitamin K3), the synthetic analog of vitamin K, being water soluble, is advised in intestinal malabsorption or in states in which bile flow is deficient. The primary disadvantage is that it takes 24 h to initiate therapeutic effects, however, this effect lasts for several days. The dose is 5–40 mg orally, daily. Menadiol sodium phosphate, even in moderate doses, may lead to hemolytic anemia and, for this reason, neonates should not receive this medication. This precautionary measure is valid especially those that are deficient in glucose 6-phosphate dehydrogenase (G6PD); their immature livers are unable to compensate for the heavy bilirubin load and there is an increased risk of kernicterus.

Vitamin K is heavily metabolized in the liver and excreted in the urine and bile. In tracer studies, it was found that approximately 20% of an injected dose of phylloquinone (Vitamin K metabolite) was found in the urine whereas about 40-50 % was excreted in the feces via the biliary system. The proportion of drug excreted was the same regardless of whether the injected dose was 1 mg or 45 µg. It can, therefore, be inferred that about 60-70% percent of the amounts of phylloquinone absorbed from each vitamin-K containing meal will be lost to the body by excretion. Two major human excretion products have been identified: carboxylic acids with 5 and 7-carbon sidechains that are excreted in the urine as glucuronide conjugates. The biliary metabolites have not been clearly identified but are initially excreted as water-soluble conjugates and become lipid soluble during their passage through the gut, probably through deconjugation by the gut flora. There is no evidence for body stores of vitamin K being conserved by an enterohepatic circulation. Vitamin K itself is too lipophilic to be excreted in the bile and the sidechain-shortened carboxylic acid metabolites are not biologically active.

In a study of rabbits, the apparent volume of distribution (V(d)/F) in plasma was 30.833 ± 12.835 L.

The plasma clearance (CL/F) of VK3 was 0.822 ± 0.254 L min-1.