Drug Groups

approved

Description

Injectable form of vitamin B 12 that has been used therapeutically to treat vitamin B 12 deficiency. [PubChem]

Indication

For treatment of pernicious anemia and the prevention and treatment of vitamin B12 deficiency arising from alcoholism, malabsorption, tapeworm infestation, celiac, hyperthyroidism, hepatic-biliary tract disease, persistent diarrhea, ileal resection, pancreatic cancer, renal disease, prolonged stress, vegan diets, macrobiotic diets or other restrictive diets. Also for the treatment of known or suspected cyanide poisoning.

Pharmacology

Hydroxocobalamin is a synthetic, injectable form of Vitamin B12. Hydroxocobalamin is actually a precursor of two cofactors or vitamins (Vitamin B12 and Methylcobalamin) which are involved in various biological systems in man. Vitamin B12 is required for the conversion of methylmalonate to succinate. Deficiency of this enzyme could therefore interfere with the production of lipoprotein in myelin sheath tissue and so give rise to neurological lesions. The second cofactor, Methylcobalamin, is necessary for the conversion of homocysteine to methionine which is essential for the metabolism of folic acid. Deficiency of tetrahydrafolate leads to reduced synthesis of thymidylate resulting in reduced synthesis of DNA which is essential for cell maturation. Vitamin B12 is also concerned in the maintenance of sulphydryl groups in reduced form, deficiency leading to decreased amounts of reduced SH content of erythrocytes and liver cells. Overall, vitamin B12 acts as a coenzyme for various metabolic functions, including fat and carbohydrate metabolism and protein synthesis. It is necessary for growth, cell replication, hematopoiesis, and nucleoprotein as well as myelin synthesis. This is largely due to its effects on metabolism of methionine folic acid, and malonic acid.

Affected Organisms

Biotransformation

Primarily hepatic. Cobalamins are absorbed in the ileum and stored in the liver. They continuously undergo enterohepatic recycling via secretion in the bile. Part of a dose is excreted in the urine, most of it in the first 8 hours.

Absorption

Readily absorbed from the gastrointestinal tract, except in malabsorption syndromes. Vitamin B12 is absorbed in the lower half of the ileum.

Half Life

Approximately 6 days (peak plasma concentration after 8-12 hours from oral administration)

Protein Binding

Very high (90%). Cobalamins are extensively bound to two specific plasma proteins called transcobalamin 1 and 2; 70% to transcobalamin 1, 5% to transcobalamin 2.

Elimination

Each hydroxocobalamin molecule can bind one cyanide ion by substituting it for the hydroxo ligand linked to the trivalent cobalt ion, to form cyanocobalamin, which is then excreted in the urine.

References

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