USP(U.S. Pharmacopela / National Formulary)
VITAMIN K;Synkavite;2-methyl-3-[(E)-3,7,11,15-tetramethylhexadec-2-enyl]naphthalene-1,4-dione;Vitamin K substances;C01628;Kanavit;vitamine K;VITAMIN K1 USP23
The half-life of vitamin K1 is quite short—only 1.7 hours via the intravenous route and 3–5 hours via the oral route. When given orally, vitamin K1 is absorbed directly from the proximal small intestine in an energy-dependent and saturable process that requires the presence of bile salts. These kinetic features argue for administration in divided doses rather than larger, single daily doses. The typical starting point for adults with drug-induced hypoprothrombinemia is 2.5 to 10 mg of vitamin K1 orally, repeating in 12 to 48 hours if needed. In cases of ingestion of long-acting superwarfarin rodenticides (e.g., brodifacoum), therapy may be 125 mg/day for weeks or months. Practically speaking, because vitamin K1 is dispensed as 5-mg tablets, superwarfarin-poisoned patients may require 10 to 30 tablets every 6 hours.
Vitamin K antagonists, such as warfarin, produce their effect on blood coagulation by interfering with the cyclic interconversion of vitamin K and vitamin K 2,3-epoxide. Vitamin K is an essential cofactor necessary for the posttranslational carboxylation of the glutamic acid residues on the N-terminal portions of the specific clotting factors (II, VII, IX, and X) and anticoagulant proteins, such as protein C. This γ-glutamyl carboxylation results in a new amino acid, γ-carboxyglutamate, which through chelation of calcium ions causes the proteins to undergo a conformational change. This change in tertiary structure allows the four vitamin K–dependent clotting factors to become activated and bind to the negatively charged phospholipid membranes during clotting cascade activation.