Vitamin K is a fat-soluble compound with potent antihemorrhagic activity that regulates hemostasis. It is required by the liver for the synthesis of key plasma clotting factors and plays a role in bone tissue formation. In pharmacotherapy, its preparations are used to treat and prevent hemorrhagic syndromes.
Main EffectEnsures blood coagulation (antihemorrhagic action).
Factor SynthesisParticipates in the hepatic formation of factors II, VII, IX, X, and protein C.
Bone TissueParticipates in the biosynthesis of the calcium-binding protein osteocalcin.
PreparationsPhytomenadione (vitamin K₁) and menadione sodium bisulfite (vitamin K₃).
Classification and Dietary Sources
The vitamin K group unites several chemical forms that differ in their origin:
Vitamin $K_1$ (phylloquinone) — obtained from plant-based foods in the diet. Its primary sources include leafy greens (sorrel, spinach, cabbage), vegetable oils (corn), certain root vegetables (potatoes, beets, carrots), and bananas.
Vitamin $K_2$ (menaquinone) — synthesized by normal intestinal microflora. Dietary sources include beef liver, milk, cheese, and eggs.
Vitamin $K_3$ (menadione) — a synthetic analog.
In medical practice, pharmacological preparations used include Phytomenadione (corresponding to natural vitamin $K_1$) and Menadione sodium bisulfite (representing vitamin $K_3$).
Physiological Role and Mechanism of Action
The biological significance of this compound lies in ensuring blood coagulation and bone mineralization processes:
Role in Hemostasis (hepatic effects): The substance is required for the biosynthesis of specific clotting factor proteins in the liver:
Factor II (prothrombin);
Factor VII (proconvertin);
Factor IX (Christmas factor);
Factor X (Stuart-Prower factor);
Protein C (a natural anticoagulant factor).
Extrahepatic effects: The vitamin participates in the formation of osteocalcin, a protein that binds calcium in bone tissue.
Indications for Clinical Use
Administration of these agents is indicated to correct hemorrhagic syndromes caused by prothrombin deficiency (hypoprothrombinemia).
Category of Causes
Clinical Situations
Liver and Biliary Tract Pathologies
Liver cirrhosis, hepatitis (impaired protein synthesis); obstructive jaundice (decreased absorption due to lack of bile)
Absorption Disorders
Malabsorption syndrome
Medication Complications
Overdose of indirect anticoagulants (vitamin K antagonists)
Prophylactic Purposes
Prevention of hemorrhagic disease of the newborn; preparation for major surgical procedures
Mnemonic
Remember the key hepatic hemostatic factors dependent on vitamin K: factors II (prothrombin), VII (proconvertin), IX (Christmas), X (Stuart-Prower), and the anticoagulant protein C.
Frequently asked questions
What is the molecular mechanism of action of vitamin K on blood clotting factors?
Vitamin K acts as a cofactor in the carboxylation of glutamic acid residues in the prothrombin molecule and other clotting factors. The active form of the vitamin—hydroquinone—is oxidized to an inactive epoxide during carboxylation, ensuring the formation of gamma-carboxyglutamic acid. Gamma-carboxyglutamate residues bind calcium ions, allowing clotting factors to anchor to negatively charged cell membrane phospholipids. To be reused, the epoxide is reduced back to hydroquinone by reductase enzymes.
How do the pharmacokinetic properties of phytomenadione and menadione sodium bisulfite differ?
The pharmacokinetic properties differ based on their gastrointestinal absorption requirements. Natural vitamin $K_1$ and its synthetic analog phytomenadione are fat-soluble compounds requiring bile for intestinal absorption. In contrast, water-soluble agents do not require bile for absorption.
What side effects are associated with menadione sodium bisulfite administration?
Administration of these vitamin preparations can cause the following adverse reactions:
Anaphylactoid reactions (reactiones anaphylactoides) — risk associated with intravenous administration.
Hemolytic anemia and hyperbilirubinemia (anaemia haemolytica et hyperbilirubinaemia) — specific toxicity in newborns when vitamin $K_3$ is used.
What are the contraindications to prescribing vitamin K preparations?
Vitamin K preparations have specific contraindications. They are strictly contraindicated during pregnancy due to their ability to easily cross the placental barrier and exert potential teratogenic effects on the fetus.
Why does obstructive jaundice lead to bleeding that requires vitamin K administration?
In obstructive jaundice, bile fails to reach the intestinal lumen, which severely impairs the absorption of the fat-soluble vitamin K. This leads to reduced hepatic synthesis of prothrombin and other clotting factors.
Which preparation is classified as a synthetic analog of vitamin K?
The synthetic analog is menadione sodium bisulfite, which corresponds to vitamin $K_3$.
What are the primary medical indications for phytomenadione use?
The drug is used to reverse bleeding caused by an overdose of indirect anticoagulants (which act as direct vitamin K antagonists), as well as in hepatitis, cirrhosis, and malabsorption syndrome.
Go deeper
Comparative characteristics of Phytomenadione (K₁) and Menadione (K₃)
Mechanism of hemorrhagic disease of the newborn and its prevention
Pharmacodynamic interaction of vitamin K antagonists and indirect anticoagulants
The role of osteocalcin in the extrahepatic effects of vitamin K