Pharmacotherapeutic Group: Vitamin, Antianemic. ATC code: B03BA05.
Pharmacology: Pharmacodynamics: Methydon contains Methylcobalamin which is an essential water soluble vitamin B also known as vitamin B12. Vitamin B12 is required for nuclear-protein and myelin synthesis, cell reproduction, normal growth, and normal erythropoiesis. Vitamin B12 is converted to coenzyme B12, which is essential for the conversion of methylmalonate to succinate, and the synthesis of methionine from homocysteine. Vitamin B12 is involved in maintaining sulfhydryl groups in the reduced form required by enzymes involved in fat and carbohydrate metabolism, and protein synthesis. Vitamin B12 is involved in folate synthesis and a deficiency of methylcobalamin results in a functional folate deficiency. Vitamin B12 is required as part of the remethylation of homocysteine to methionine. Elevated levels of homocysteine has been linked to the increase risk of endothelial cell damage, impaired endothelial-dependent vasodilation due to reduced nitric oxide activity, increased oxidation and arterial deposition of low-density lipoproteins (LDL), increased platelet adhesiveness, and activation of the clotting cascade. Vitamin B12 supplements have a small additive effect to folic acid in lowering fasting homocysteine levels, but probably only in people with vitamin B12 deficiency. Elevated homocysteine concentrations are possibly associated with other conditions such as decreased cognitive function, impaired memory, Alzheimer's disease, and vascular dementia. The methylcobalamin form of vitamin B12 might also influence melatonin levels. Methylcobalamin seems to improve alertness and reduce sleep time in humans with normal sleep patterns, possibly due to effects on melatonin.
Pharmacokinetics: Vitamin B12 is absorbed via an active transport mechanism in the terminal ileum. This requires the glycoprotein, intrinsic factor, which is produced by the stomach. At normal gastric pH, vitamin B12 is cleaved from proteins in food. It then binds to intrinsic factor and is absorbed by ideal transport. Absorption may be reduced by increased gastric pH such as atrophic gastritis, use of acid-suppressing drugs, or partial gastrectomy. The half-life of vitamin B12 is 6 hours and is secreted mainly via the bile.