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Clinical data
Pronunciationsye AN oh koe BAL a min[3]
Trade namesCobolin-M,[3] Depo-Cobolin,[3] others[4]
AHFS/Drugs.comFDA Professional Drug Information
  • US: C (Risk not ruled out)
Routes of
By mouth, intramuscular, nasal spray[1][2]
ATC code
CAS Number
PubChem CID
ECHA InfoCard100.000.618 Edit this at Wikidata
Chemical and physical data
Molar mass1355.38 g/mol
3D model (JSmol)
Melting point300 °C (572 °F) +
Boiling point300 °C (572 °F) +
Solubility in water1/80g/ml

Cyanocobalamin is a manufactured form of vitamin used to treat vitamin B12 deficiency.[3] The deficiency may occur in pernicious anemia, following surgical removal of the stomach, with fish tapeworm, or due to bowel cancer.[5] It is less preferred than hydroxocobalamin for treating vitamin B12 deficiency.[1] It is used by mouth, by injection into a muscle, or as a nasal spray.[1][2]

Cyanocobalamin is generally well tolerated.[6] Minor side effects may include diarrhea and itchiness.[7] Serious side effects may include anaphylaxis, low blood potassium, and heart failure.[7] Use is not recommended in those who are allergic to cobalt or have Leber's disease.[5] Vitamin is an essential nutrient meaning that it cannot be made by the body but is required for life.[8][6]

Cyanocobalamin was first manufactured in the 1940s.[9] It is available as a generic medication and over the counter.[1][6] In the United Kingdom it costs the NHS about 2.90 £ per injection as of 2019.[1] In the United States the wholesale cost of this amount was about US$0.77 in 2019.[10] In 2016 it was the 137th most prescribed medication in the United States with 5 million prescriptions.[11]

Medical use

Cyanocobalamin is usually prescribed after surgical removal of part or all of the stomach or intestine to ensure adequate serum levels of vitamin . It is also used to treat pernicious anemia, vitamin deficiency (due to low intake from food), thyrotoxicosis, hemorrhage, malignancy, liver disease and kidney disease. Cyanocobalamin injections are often prescribed to gastric bypass patients who have had part of their small intestine bypassed, making it difficult for to be acquired via food or vitamins. Cyanocobamide is also used to perform the Schilling test to check ability to absorb vitamin .[12]

Side effects

Possible side effects of cyanocobalamin injection include allergic reactions such as hives, difficult breathing; redness of the face; swelling of the arms, hands, feet, ankles or lower legs; extreme thirst; and diarrhea. Less-serious side effects may include headache, dizziness, leg pain, itching, or rash.[13]

Treatment of megaloblastic anemia with concurrent vitamin deficiency using vitamers (including cyanocobalamin), creates the possibility of hypokalemia due to increased erythropoiesis (red blood cell production) and consequent cellular uptake of potassium upon anemia resolution.[14] When treated with vitamin , patients with Leber's disease may suffer serious optic atrophy, possibly leading to blindness.[15]


Vitamin is the "generic descriptor" name for any vitamers of vitamin . Animals, including humans, can convert cyanocobalamin to any one of the active vitamin compounds.[16]

Cyanocobalamin is one of the most widely manufactured vitamers in the vitamin family (the family of chemicals that function as when put into the body), because cyanocobalamin is the most[] air-stable of the forms. It is the easiest[] to crystallize and therefore easiest[] to purify after it is produced by bacterial fermentation, or synthesized in vitro. It can be obtained as dark red crystals or as an amorphous red powder. Cyanocobalamin is hygroscopic in the anhydrous form, and sparingly soluble in water (1:80).[] It is stable to autoclaving for short periods at 121 °C (250 °F). The vitamin coenzymes are unstable in light. After consumption the cyanide ligand is replaced by other groups (adenosyl, methyl), which are the biologically active forms. The cyanide is converted to thiocyanate and excreted by the kidney.[]

Chemical reactions

Reduced forms of Cyanocobalamin, with a Co(I) (top), Co(II) (middle), and Co(III) (bottom)

In the cobalamins, cobalt normally exists in the trivalent state, Co(III). However, under reducing conditions, the cobalt center is reduced to Co(II) or even Co(I), which are usually denoted as and , for reduced and super reduced, respectively.

and can be prepared from cyanocobalamin by controlled potential reduction, or chemical reduction using sodium borohydride in alkaline solution, zinc in acetic acid, or by the action of thiols. Both and are stable indefinitely under oxygen-free conditions. appears orange-brown in solution, while appears bluish-green under natural daylight, and purple under artificial light.[17]

is one of the most nucleophilic species known in aqueous solution.[] This property allows the convenient preparation of cobalamin analogs with different substituents, via nucleophilic attack on alkyl halides and vinyl halides.[17]

For example, cyanocobalamin can be converted to its analog cobalamins via reduction to , followed by the addition of the corresponding alkyl halides, acyl halides, alkene or alkyne. Steric hindrance is the major limiting factor in the synthesis of the coenzyme analogs. For example, no reaction occurs between neopentyl chloride and , whereas the secondary alkyl halide analogs are too unstable to be isolated.[17] This effect may be due to the strong coordination between benzimidazole and the central cobalt atom, pulling it down into the plane of corrin ring. The trans effect determines the polarizability of the Co-C bond so formed. However, once the benzimidazole is detached from cobalt by quaternization with methyl iodide, it is replaced by or hydroxyl ions. Various secondary alkyl halides are then readily attacked by the modified to give the corresponding stable cobalamin analogs.[18] The products are usually extracted and purified by phenol-methylene chloride extraction or by column chromatography.[17]

Cobalamin analogs prepared by this method include the naturally occurring coenzymes methylcobalamin and cobamamide, and other cobalamins that do not occur naturally, such as vinylcobalamin, carboxymethylcobalamin and cyclohexylcobalamin.[17] This reaction is under review for use as a catalyst for chemical dehalogenation, organic reagent and photosensitized catalyst systems.[19]


Cyanocobalamin is commercially prepared by bacterial fermentation. Fermentation by a variety of microorganisms yields a mixture of methyl-, hydroxo- and adenosylcobalamin. These compounds are converted to cyanocobalamin by addition of potassium cyanide in the presence of sodium nitrite and heat. Since multiple species of Propionibacterium produce no exotoxins or endotoxins and have been granted GRAS status (generally regarded as safe) by the United States Food and Drug Administration, they are the preferred bacterial fermentation organisms for vitamin production.[20]

Historically, a form of vitamin called hydroxocobalamin is often produced by bacteria and was then changed to cyanocobalamin during purification in activated charcoal columns after separation from the bacterial cultures. This change was not immediately realized when vitamin was first extracted for characterization.[clarify]Cyanide is naturally present in activated charcoal. Hydroxocobalamin, which has affinity for cyanide, picks it up and changes to cyanocobalamin. Cyanocobalamin is the form in most pharmaceutical preparations because adding cyanide stabilizes the molecule.[21]

As of 2000, France accounted for 80% of the world's 10+ tonnes/year of production. 55% of sales is destined for animal feed, while the remaining 45% is for human consumption.[22]


The two bioactive forms of vitamin are methylcobalamin in cytosol and adenosylcobalamin in mitochondria. Multivitamins often contain cyanocobalamin, which is presumably converted to bioactive forms in the body. Both methylcobalamin and adenosylcobalamin are commercially available as supplement pills. The MMACHC gene product catalyzes the decyanation of cyanocobalamin as well as the dealkylation of alkylcobalamins including methylcobalamin and adenosylcobalamin.[23] This function has also been attributed to cobalamin reductases.[24] The MMACHC gene product and cobalamin reductases enable the interconversion of cyano- and alkylcobalamins.[25]

cyanocobalamin is added to fortify[26] nutrition, including baby milk powder, breakfast cereals and energy drinks for humans, also animal feed for poultry, swine and fish. Vitamin becomes inactive due to hydrogen cyanide and nitric oxide in cigarette smoke. Vitamin also becomes inactive due to nitrous oxide commonly known as laughing gas, used for anaesthesia and abused as a recreational drug.[27] Vitamin becomes inactive due to microwaving or other forms of heating.[28]

In the cytosol

Vitamin methylcobalamin and 5-methyltetrahydrofolate are needed by methionine synthase in the methionine cycle to transfer a methyl group from 5-methyltetrahydrofolate to homocysteine, thereby generating tetrahydrofolate (THF) and methionine, which is used to make SAMe. SAMe is the universal methyl donor and is used for DNA methylation and to make phospholipid membranes, choline, sphingomyelin, acetylcholine, and other neurotransmitters.

In mitochondria

Vitamin B12 adenosylcobalamin in mitochondrion--cholesterol and protein metabolism

The enzymes that use as a built-in cofactor are methylmalonyl-CoA mutase (PDB 4REQ[29]) and methionine synthase (PDB 1Q8J).[30]

The metabolism of propionyl-CoA occurs in the mitochondria and requires Vitamin (as adenosylcobalamin) to make succinyl-CoA. When the conversion of propionyl-CoA to succinyl-CoA in the mitochondria fails due to Vitamin deficiency, elevated blood levels of methylmalonic acid (MMA) occur. Thus, elevated blood levels of homocysteine and MMA may both be indicators of vitamin deficiency.

Vitamin adenosylcobalamin is needed as cofactor in methylmalonyl-CoA mutase--MUT enzyme. Processing of cholesterol and protein gives propionyl-CoA that is converted to methylmalonyl-CoA, which is used by MUT enzyme to make succinyl-CoA. Vitamin is needed to prevent anemia, since making porphyrin and heme in mitochondria for producing hemoglobin in red blood cells depends on succinyl-CoA made by vitamin .

Absorption and transport

Poor absorption of vitamin may be related to coeliac disease. Intestinal absorption of vitamin requires successively three different protein molecules: haptocorrin, intrinsic factor and transcobalamin II.


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