B12 Sr

Uses

This preparation is used for Pernicious anemia,Vitamin B12 deficiency due to low intake from food,Thyrotoxicosis, Hemorrhage, Malignancy, Liver or kidney disease,Gastric bypass surgery, Total or partial gastrectomy, Gluten enteropathy or sprue, Folic acid deficiency, Macrocytic anaemia

B12 Sr is also used to associated treatment for these conditions: Anemia, Anemia, Pernicious, Combined Vitamin B1 and B12 deficiency, Convalescence, Diabetic Neuropathies, Folate deficiency, Iron Deficiency Anemia (IDA), Neuritis, Vitamin B1 deficiency, Vitamin B12 Deficiency, Vitamin B12 concentration, Vitamin B6 Deficiency, Vitamin Deficiency, Nutritional supplementation, Vitamin supplementation

How B12 Sr works

Vitamin B12 serves as a cofactor for methionine synthase and L-methylmalonyl-CoA mutase enzymes. Methionine synthase is essential for the synthesis of purines and pyrimidines that form DNA. L-methylmalonyl-CoA mutase converts L-methylmalonyl-CoA to succinyl-CoA in the degradation of propionate , an important reaction required for both fat and protein metabolism. It is a lack of vitamin B12 cofactor in the above reaction and the resulting accumulation of methylmalonyl CoA that is believed to be responsible for the neurological manifestations of B12 deficiency . Succinyl-CoA is also necessary for the synthesis of hemoglobin .

In tissues, vitamin B12 is required for the synthesis of methionine from homocysteine. Methionine is required for the formation of S-adenosylmethionine, a methyl donor for nearly 100 substrates, comprised of DNA, RNA, hormones, proteins, as well as lipids . Without vitamin B12, tetrahydrofolate cannot be regenerated from 5-methyltetrahydrofolate, and this can lead to functional folate deficiency , . This reaction is dependent on methylcobalamin (vitamin B12) as a co-factor and is also dependent on folate, in which the methyl group of methyltetrahydrofolate is transferred to homocysteine to form methionine and tetrahydrofolate. Vitamin B12 incorporates into circulating folic acid into growing red blood cells; retaining the folate in these cells . A deficiency of vitamin B12 and the interruption of this reaction leads to the development of megaloblastic anemia.

Dosage

B12 Sr dosage

Usual Adult Dose for Pernicious Anemia

Initial dose: 1000 mcg intramuscularly or deep subcutaneous once a day for 6 to 7 daysIf clinical improvement and reticulocyte response is seen from the above dosing:

• 100 mcg every other day for 7 doses, then
• 100 mcg every 3 to 4 days for 2 to 3 weeks, then
• Maintenance dose: 100 to 1000 mcg monthly

Administer concomitant folic acid if needed. Chronic treatment should be done with an oral preparation in patients with normal intestinal absorption.

Usual Adult Dose for B12 Nutritional Deficiency: 25 to 2000 mcg orally daily

Usual Adult Dose for Schilling Test: 1000 mcg intramuscularly is the flushing dose

Usual Pediatric Dose for B12 Nutritional Deficiency: 0.5 to 3 mcg daily

Side Effects

Arthralgia (12%), Dizziness (12%), Headache (12%), Nasopharyngitis (12%), Anaphylaxis, Angioedema, Congestive heart failure, Peripheral vascular disease,Pulmonary edema, Diarrhea, Dyspepsia, Polycythemia vera, Sore throat, Nervousness, Rhinitis, Glossitis, Hypoesthesia

Toxicity

LD50 Oral (mouse): > 5,000 mg/kg .

General toxicity

Vitamin B12 is generally non-toxic, even at higher doses. Mild, transient diarrhea, polycythemia vera, peripheral vascular thrombosis, itching, transitory exanthema, a feeling of swelling of entire body, pulmonary edema and congestive heart failure in early treatment stages, anaphylactic shock and death have been observed after vitamin B12 administration .

Carcinogenesis and mutagenesis

Long term studies in animals examining the carcinogenic potential of any of the vitamin B12 formulations have not completed to date. There is no evidence from long-term use in patients with pernicious anemia that vitamin B12 has carcinogenic potential. Pernicious anemia is known to be associated with an increased incidence of stomach carcinoma, however, this malignancy has been attributed to the underlying cause of pernicious anemia and has not been found to be related to treatment with vitamin B12 .

Use in pregnancy

No adverse effects have been reported with ingestion of normal daily requirements during pregnancy .

A note on the use of the nasal spray in pregnancy

Although vitamin B12 is an essential vitamin and requirements are increased during pregnancy, it is currently unknown whether the nasal spray form can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. The nasal spray form should be given to a pregnant woman only if clearly needed, as it is considered a pregnancy category C drug in this form. Sufficient well-controlled studies have not been done to this date in pregnant women .

Use in lactation

Vitamin B12 has been found distributed into the milk of nursing women in concentrations similar to the maternal blood vitamin B12 concentrations. No adverse effects have been reported to date with intake of normal required doses during lactation .

Precaution

Intensive treatment of B12-deficient megaloblastic anemia may cause hypokalemia and sudden death. Use with caution in patients with Leber optic nerve atrophy. Thrombocytosis may occur with treatment of severe vitamin B12 megaloblastic anemia

Interaction

Absorption reduced by antibiotics, aminosalicylic acid, anticonvulsants, biguanides, cholestyramine, cimetidine, colchicine, K salts, methyldopa.

Food Interaction

• Take with or without food. Recommendations vary from product to product - consult individual product monographs for additional information.

B12 Sr Disease Interaction

Major: hypokalemia, optic nerveModerate: malabsorption, renal impairment

Volume of Distribution

Cobalamin is distributed to tissues and stored mainly in the liver and bone marrow .

Elimination Route

Vitamin B12 is quickly absorbed from intramuscular (IM) and subcutaneous (SC) sites of injection; with peak plasma concentrations achieved about 1 hour after IM injection .

Orally administered vitamin B12 binds to intrinsic factor (IF) during its transport through the stomach. The separation of Vitamin B12 and IF occurs in the terminal ileum when calcium is present, and vitamin B12 is then absorbed into the gastrointestinal mucosal cells. It is then transported by transcobalamin binding proteins . Passive diffusion through the intestinal wall can occur, however, high doses of vitamin B12 are required in this case (i.e. >1 mg). After the administration of oral doses less than 3 mcg, peak plasma concentrations are not reached for 8 to 12 hours, because the vitamin is temporarily retained in the wall of the lower ileum .

Half Life

Approximately 6 days (400 days in the liver) .

Clearance

During vitamin loading, the kidney accumulates large amounts of unbound vitamin B12. This drug is cleared partially by the kidney, however, multiligand receptor megalin promotes the reuptake and reabsorption of vitamin B12 into the body , .

Elimination Route

This drug is partially excreted in the urine . According to a clinical study, approximately 3-8 mcg of vitamin B12 is secreted into the gastrointestinal tract daily via the bile. In patients with adequate levels of intrinsic factor, all except approximately 1 mcg is reabsorbed. When vitamin B12 is administered in higher doses that saturate the binding capacity of plasma proteins and the liver, the unbound vitamin B12 is eliminated rapidly in the urine. The body storage of vitamin B12 is dose-dependent .

Pregnancy & Breastfeeding use

Pregnancy Category A. Adequate and well-controlled human studies have failed to demonstrate a risk to the fetus in the first trimester of pregnancy (and there is no evidence of risk in later trimesters).

Lactation: Drug distributed in milk.

Contraindication

Leber's disease, tobacco amblyopia.

Innovators Monograph

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