Classification and sources
The vitamin K group unites several chemical forms that differ in their origin:
- Vitamin $K_1$ (phylloquinones) — enters the body from plant-based foods. Its primary sources are leafy vegetables (sorrel, spinach, cabbage), vegetable oils (corn), certain root vegetables (potatoes, beets, carrots), and bananas.
- Vitamin $K_2$ (menaquinones) — synthesized by healthy intestinal microflora. Dietary sources include beef liver, milk, cheese, and eggs.
- Vitamin $K_3$ (menadione) — a synthetic analogue.
In medical practice, the following pharmacological preparations are used: Phytomenadione (corresponds to natural vitamin $K_1$) and Menadione sodium bisulfite (trade name — Vikasol, represents vitamin $K_3$).
Physiological role and mechanism of action
The biological significance of the compound lies in ensuring blood coagulation and bone mineralization processes:
- Role in hemostasis (hepatic effects): the substance is necessary for the biosynthesis of specific protein coagulation factors in the liver:
- Factor II (prothrombin);
- Factor VII (proconvertin);
- Factor IX (Christmas factor);
- Factor X (Stuart-Prower factor);
- Protein C (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
The administration of preparations is indicated to correct hemorrhagic syndrome caused by prothrombin deficiency (hypoprothrombinemia).
| Category of causes | Clinical situations |
|---|---|
| Pathologies of the liver and biliary tract | Liver cirrhosis, hepatitis (impaired protein synthesis); obstructive jaundice (impaired absorption due to the absence of bile) |
| Malabsorption disorders | Malabsorption syndrome |
| Drug-induced complications | Overdose of indirect anticoagulants (vitamin K antagonists) |
| Prophylactic purposes | Prevention of hemorrhagic disease of the newborn; preparation for major surgical interventions |
Briefly: answers to topical questions
What is the molecular mechanism of action of vitamin K on blood coagulation factors?
Vitamin K acts as a coenzyme 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 inactive epoxide during carboxylation, ensuring the formation of gamma-carboxyglutamic acid. Gamma-carboxyglutamate residues bind calcium ions, which allows clotting factors to anchor to negatively charged phospholipids of cell membranes. For reuse, the epoxide is reduced back to hydroquinone by reductase enzymes.
What are the pharmacokinetic differences between phytonadione and menadione sodium bisulfite?
The pharmacokinetic properties of the drugs differ due to their absorption characteristics in the gastrointestinal tract. Natural vitamin $K_1$ and its synthetic analog phytonadione are fat-soluble compounds, the intestinal absorption of which requires bile. At the same time, water-soluble drugs such as menadione sodium bisulfite do not require the presence of bile for absorption.
What adverse effects are typical for the use of menadione sodium bisulfite?
The use of vitamin drugs leads to the following adverse reactions:
- Allergic reactions (reactiones allergicae) — skin rash, pruritus, erythema, and bronchospasm.
- Anaphylactoid reactions (reactiones anaphylactoides) — risk of occurrence with intravenous administration.
- Hemolytic anemia and hyperbilirubinemia (anaemia haemolytica et hyperbilirubinaemia) — specific toxicity in newborns when using vitamin $K_3$ and menadione sodium bisulfite.
What are the contraindications for prescribing vitamin K preparations?
Vitamin K preparations have absolute contraindications for use. They are strictly contraindicated during pregnancy due to their ability to easily cross the placental barrier and exert a teratogenic effect on the fetus.
Remember the key vitamin K-dependent hepatic factors of hemostasis: factors II (prothrombin), VII (proconvertin), IX (Christmas factor), X (Stuart-Prower factor), and the anticoagulant protein C.
Class and exam questions
Why do bleeding disorders requiring vitamin K administration develop in obstructive jaundice?
In obstructive jaundice, bile does not enter the intestine, which drastically impairs the absorption of fat-soluble vitamin K. This leads to decreased synthesis of prothrombin and other clotting factors in the liver.
Which drug is a synthetic analog of vitamin K?
Menadione sodium bisulfite is a synthetic analog available under the trade name Vikasol (corresponds to vitamin $K_3$).
What are the main medical indications for the use of phytonadione?
The drug is used to stop bleeding in case of an overdose of indirect anticoagulants, which are direct antagonists of vitamin K, as well as in hepatitis, cirrhosis, and malabsorption syndrome.
What else to study on this topic
- Comparative characteristics of Phytonadione ($K_1$) and Menadione sodium bisulfite ($K_3$)
- Mechanism of development 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
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