Vitamin B12

Origin and sources

Vitamin B12 has a unique distinctive feature among all vitamins: it is completely absent in plant foods. This is a crucial fact to consider when taking a medical history and assessing a patient's diet. In the human body, it is synthesized by the normal intestinal microflora, but this is insufficient to fully meet physiological needs. The main pool of the substance enters the body via the alimentary route exclusively from animal-derived products. It is most abundant in offal (liver and kidneys), as well as meat, various fish, seafood, egg yolk, and cheese.

Dosage forms and complex pharmacokinetics

The pharmacological arsenal includes three main drug forms: standard cyanocobalamin, its active coenzyme form — cobamamide, and hydroxocobalamin (oxycobalamin).

The assimilation process of the vitamin is a complex cascade. The key condition for its absorption is the presence of «Castle's intrinsic factor». This is a specific gastromucoprotein secreted by the parietal cells of the gastric mucosa. Without interacting with this factor, the vitamin passes through the digestive tract in transit. Following successful absorption into the bloodstream, the drug binds to specialized transport proteins — transcobalamins, which deliver it to target tissues. Intracellular bioactivation takes place: the substance transforms into its active working form — cobamamide.

Pharmacodynamics: from blood to nerves

The drug exhibits a pronounced anti-anemic effect, functioning as a vital coenzyme in a number of metabolic processes:

• Regulation of hemopoiesis. The vitamin is critically important for normal hematopoiesis. It closely interacts with folates, ensuring the formation of tetrahydrofolic acid (the active form of folic acid). It is this mechanism that triggers the processes of proliferation, proper differentiation, and the final maturation of erythrocytes.
• Neurotropic effect. The substance is responsible for maintaining the structure and formation of myelin — the insulating sheaths of nerve fibers, which ensures normal impulse conduction.
• Anabolic effects. The drug stimulates the synthesis of proteins and carbohydrates and actively participates in the regulation of lipid metabolism.

Deficiency pathology and clinical application

The main problem associated with deficiency is gastric disorders that impair the production of Castle's factor. As a result, a specific pathology develops — pernicious (malignant) anemia.

Indications for prescribing Cyanocobalaminum preparations cover several medical fields:

1. Hematology: The primary indication is pernicious anemia. The drug is also included in combination therapy for other types of anemia.
2. Neurology: Due to its effect on myelin synthesis, the vitamin is highly effective in treating polyneuritis, radiculitis, and various neuralgias.
3. Internal medicine: Anabolic properties allow its use in dystrophic myocardial changes, as well as in severe liver diseases, including hepatitis and cirrhosis.

Class and exam questions

What else to study on this topic

• The biochemical mechanism of the conversion of cyanocobalamin into cobamamide.
• The pathogenesis of pernicious (malignant) anemia in Castle's factor deficiency.
• The role of transcobalamins in the blood transport system.
• The interaction of vitamin B12 and folates during erythrocyte maturation.
• Comparative characteristics of hydroxocobalamin and cyanocobalamin.

Other topics in the "Vitamins" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.