Cyanocobalamin (Vitamin B12) Injection

Cyanocobalamin is a vital compound for cell division and growth, hematopoiesis, and nucleoprotein and myelin synthesis. This vitamin also has an important role in protein synthesis, neural metabolism, DNA and RNA production, as well as fat and carbohydrate metabolism. Several cells appear to have the greatest demand for cyanocobalamin, particularly those that undergo rapid division such as bone marrow and epithelial cells.

Cyanocobalamin binds itself to plasma proteins in the systemic circulation. It attaches with specific cobalamin binding proteins, called transcobalamin I and II, to enter into the tissues. In cells, this vitamin functions as a cofactor for two vital enzymatic reactions: (1) methionine synthase, i.e. the regeneration of methionine from homocysteine and (2) methylmalonyl-CoA mutase, i.e. the isomerization of methylmalonyl-CoA to succinyl-CoA. Both these methylation reactions are vital for growth and cell reproduction.

Methionine, a sulfur-containing, essential amino acid, is a precursor of S-adenosylmethionine, a cofactor for one-carbon metabolism and the final methyl donor for the methylation of DNA, RNA, proteins, and phospholipids. The methionine synthase plays a paramount role in the synthesis of nitrogenous bases (purines and pyrimidines) involved in the formation of DNA. The lack of adequate cobalamin in the body hinders the regeneration of tetrahydrofolate, which eventually leads to megaloblastic anemia due to the functional folate deficiency.On the other hand, the methylmalonyl-CoA mutase helps to metabolize odd chain fatty acids and branch chain amino acids. Cobalamin is also thought to keep the body’s level of sulfhydryl (SH) groups in reduced form. SH groups activate many enzyme systems involved in protein synthesis as well as fat and carbohydrate metabolism. If there is a lack of cobalamin in the body, methylmalonyl CoA accumulates, which presumably leads to the neurological manifestations of B12 deficiency.

The replenishment with parenteral cyanocobalamin causes a rapid and complete improvement of megaloblastic anemia and gastrointestinal symptoms caused by vitamin B12 deficiency. The parenteral administration also halts the progression of neurological damage associated with B12 deficiency, but the complete improvement of the condition may depend on the severity and extent of the deficiency.

Cyanocobalamin is contraindicated in those with hypersensitivity to cobalt moiety or cobalamin molecule due to the risk of anaphylaxis.

Warnings:

• The use of cyanocobalamin is warned in patients with early Leber’s disease as there have been reports of severe and swift optic atrophy with its administration. Appropriate caution should be exercised while treating severe megaloblastic anemia with cyanocobalamin as intense treatment may lead to hypokalemia and sudden death. Cautious use of parenteral cyanocobalamin is also recommended in patients with renal impairment, including premature neonates, because of the possibility of greater aluminum accumulation, which may cause central nervous system and bone toxicity. Formulations of cyanocobalamin injection containing benzyl alcohol as a preservative should also be avoided in premature neonates and those with hypersensitivity due to its association with ‘gasping syndrome.

Monitoring:

• A history of the patient’s allergies/hypersensitivity should be obtained before administering cyanocobalamin injection. If the patient is suspected to be sensitive to cobalt or other components of cobalamin, an intradermal test dose is recommended.
• Several laboratory tests should be performed prior to treatment with cyanocobalamin, including serum vitamin B12, folate, iron, hematocrit, and reticulocyte count. All these parameters need to be normal before initiating the treatment. Serum levels of vitamin B12 and peripheral blood counts should be monitored in one month. For hematocrit and reticulocyte counts, recommendations are to repeat these tests daily from the 5th to 7th days of treatment and then frequently until the hematocrit returns to a normal range.
• Both serum potassium concentrations and the platelet count need to be monitored carefully after parenteral administration of cyanocobalamin. This is because hypokalemia and thrombocytosis could occur due to the increase in erythrocyte metabolism following vitamin B12 therapy. Potassium replacement therapy should be administered if necessary.
• Patients with pernicious anemia are three times more likely to have gastric carcinoma compared to general population; thus, appropriate tests need to be carried out to rule out this condition if suspected.

Therapeutic response to cyanocobalamin may decrease due to elderly age, infection, renal insufficiency, diabetes mellitus, marrow suppressants use (e.g. chloramphenicol), and concurrent iron or folic acid deficiency. Therefore, these factors should be taken into consideration and regular monitoring should be performed in these conditions while treating vitamin B12 deficiency with cyanocobalamin.

• Vitamin B12 is known to be non-toxic even in high doses. The reported adverse reactions following parenteral administration of vitamin B12 include:
• Generalized: Anaphylaxis and death
• Cardiovascular: Pulmonary edema and congestive cardiac/heart failure during early treatment; peripheral vascular thrombosis
  Hematological: Polycythemia vera (a rare type of blood cancer)
  Gastrointestinal: Mild, transient diarrhea
  Dermatological: Itching; transitory exanthema (widespread skin rash)
  Miscellaneous: Feeling of swelling of entire body

Cyanocobalamin is a medication of the FDA pregnancy category C. Up to now, no adequate and well-controlled reproduction studies have been conducted in humans and animals to determine its effects on pregnant women. However, there is also no reports of maternal or fetal harms with the ingestion of normal daily recommended amounts during pregnancy. In fact, the requirements for vitamin B12 increase during pregnancy. Therefore, parenteral cyanocobalamin should be administered to a pregnant woman if the benefits outweigh the risks.

Cyanocobalamin is excreted in the breast milk of nursing women in levels similar to the level of vitamin B12 in maternal plasma. The distributed cyanocobalamin in breast milk has been found to be compatible with breastfeeding by the American Academy of Pediatrics. In addition, there has not been any reports of adverse effects associated with the intake of normal daily requirements of vitamin B12 during lactation. The Food and Nutrition Board, the National Academy of Sciences-National Research Council recommend that lactating women should consume 4 mcg of vitamin B12 daily.

• Store this medication at 68°F to 77°F (20°C to 25°C) and away from heat, moisture and light. Keep all medicine out of the reach of children. 
• Throw away any unused medicine after the beyond use date. Do not flush unused medications or pour down a sink or drain.