PHARMACOLOGICAL ACTION Cyanocobalamin is involved by way of its participation in the formation and metabolism of purines and pyrimidines, in the synthesis of nucleoproteins, and thus in the maintenance of normal haemopoiesis.
Vitamin B12 substances bind to intrinsic factor and are then actively absorbed from the gastro-intestinal tract. Absorption is impaired in patients with an absence of intrinsic factor. Absorption from the gastro-intestinal tract can also occur by passive diffusion. Vitamin B12 is extensively bound to specific plasma proteins called transcobalamins; transcobalamin II appears to be involved in the rapid transport of the cobalamins to tissues. It is stored in the liver, excreted in the bile and undergoes extensive enterohepatic recycling; part of an administered dose is excreted in the urine, most of it in the first 8 hours; urinary excretion, however, accounts for only a small fraction in the reduction of total body stores acquired by dietary means. Vitamin B12 diffuses across the placenta and also appears in breast milk.
After injection of cyanocobalamin a large proportion is excreted in the urine within 24 hours.
INDICATIONS Indicated in vitamin B12 deficiencies manifested by megaloblastic anaemia and neurological conditions. Pernicious anaemia and its neurological complication, subacute combined degeneration of the spinal cord. Macrocytic anaemias associated with nutritional deficiencies. Intestinal malabsorption, megaloblastosis, diet-related deficiency, post-gastrectomy. Indications for prophylaxis include strict vegetarianism, post-gastrectomy, and ileal resection and conditions of the small intestine that would predictably cause deficiency.
CONTRA-INDICATIONS Cyanocobalamin should not be given before a diagnosis has been fully established because of the possibility of masking symptoms of subacute degeneration of the spinal cord. Cyanocobalamin should not be used to treat megaloblastic anaemia of pregnancy. Cyanocobalamin should not be administered before pernicious anaemia or folic acid deficiency has been ruled out.
WARNING: Must not be administered intravenously.
DOSAGE AND DIRECTIONS FOR USE: Administered intramuscularly.
In the absence of neurological involvement, cyanocobalamin may be administered in doses of 250 to 1000 micrograms intramuscularly on alternate days for 1 to 2 weeks, then 250 micrograms weekly until the blood count returns to normal. Maintenance doses of 1000 micrograms are administered monthly.
If there is neurological involvement, cyanocobalamin may be given in doses of 1000 micrograms on alternate days and continued for as long as improvement occurs.
For the prophylaxis of anaemia associated with vitamin B12 deficiency resulting from gastrectomy or malabsorption syndromes cyanocobalamin may be given in doses of 250 to 1000 micrograms intramuscularly each month.
SIDE EFFECTS AND SPECIAL PRECAUTIONS: Allergic reactions have been reported after injection.
Vitamin B12 should be given prophylactically only when there is a reasonable indication. Dietary deficiency in the strict vegetarian, the predictable malabsorption of vitamin B12 in patients who have had a gastrectomy, and certain diseases of the small intestine constitute such indications.
Administration of cyanocobalamine doses greater than 10 micrograms daily, may produce a haematological response in patients with folate deficiency.
Long-term therapy with vitamin B12 must be evaluated at intervals of 6 to 12 months in patients who are otherwise well. If there is an additional illness or a condition that may increase the requirement for the vitamin, reassessment should be performed more frequently. It is important to monitor vitamin B12 concentrations in plasma and to obtain peripheral blood counts at intervals of 3 to 6 months to confirm the adequacy of therapy. Since refractoriness to therapy can develop at any time, evaluation must continue throughout the patient's life.
Serum concentrations may be decreased by concurrent administration of oral contraceptives. Blood concentrations of cyanocobalamin may be reduced if large doses of folic acid are taken continuously.
KNOWN SYMPTOMS OF OVERDOSAGE AND PARTICULARS OF ITS TREATMENT: None
IDENTIFICATION: A dark red solution in amber glass ampoules and vials.
10 x 1 mL; 100 x 1 mL
10 x 10 mL; 50x 10 mL; 100 x 10 mL
STORAGE INSTRUCTIONS: Protect from light. Store below 25°C.
Keep out of reach of children.
APPLICATION NUMBER: H2413 (Act 101/1965) 1 mL amber glass ampoules.
H2635 (Act 101/1965) 10 mL amber glass vials.
NAME AND BUSINESS ADDRESS OF APPLICANT: Pharmacare Limited
7 Fairclough Road
DATE OF PUBLICATION OF THIS PACKAGE INSERT: March, 1975
Updated on this site: February 2002 Current: May 2004 Source: Community Pharmacy