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Cyanocobalamin is an especially common vitamer
A vitamer of a particular vitamin is any of a number of chemical substances, each of which shows vitamin activity. Very commonly each "vitamin" is not a single chemical, but rather multiple chemical substances called vitamers, each of which is defined by its different biological activity.For...

 of the vitamin B12 family
Vitamin B12
Vitamin B12, vitamin B12 or vitamin B-12, also called cobalamin, is a water-soluble vitamin with a key role in the normal functioning of the brain and nervous system, and for the formation of blood. It is one of the eight B vitamins...

. It is the most famous vitamer of the family, because it is, in chemical terms, the most air-stable. It is the easiest to crystallize and, therefore, easiest to purify after it is produced by bacterial fermentation, or synthesized in vitro
Vitamin B12 total synthesis
Vitamin B12 total synthesis in chemistry describes the total synthesis of the complex biomolecule vitamin B12. A method first reported by the groups of Robert Burns Woodward and Albert Eschenmoser in 1973 is considered a classic in this research field....


Vitamin B12 is the name for a whole class of chemicals with vitamin B12 activity, and cyanocobalamin is only one of these. Cyanocobalamin usually does not even occur in nature, and is not one of the forms of the vitamin that are directly used in the human body (or that of any other animal). However, animals and humans can convert cyanocobalamin to active (cofactor) forms of the vitamin, such as methylcobalamin. This process happens by equilibration, as cyanocobalamin slowly loses its cyanide in surroundings that contain no cyanide.

Chemical properties

This compound is found as dark red crystals or an amorphous or crystalline red powder. Cyanocobalamin is very hygroscopic in the anhydrous form, and sparingly soluble in water (1:80). It is stable to autoclaving for short periods at 121 °C. The vitamin B12 coenzymes are very unstable in light.


Since vitamin B12 has a 40-step very difficult totally synthetic route (the longest of any vitamin), this compound is always commercially prepared instead by bacterial fermentation. Fermentation by a variety of microorganisms gives a mixture of methyl-, hydroxo-, and adenosylcobalamin. These compounds are extracted, then converted to cyanocobalamin by addition of potassium cyanide
Potassium cyanide
Potassium cyanide is an inorganic compound with the formula KCN. This colorless crystalline compound, similar in appearance to sugar, is highly soluble in water. Most KCN is used in gold mining, organic synthesis, and electroplating. Smaller applications include jewelry for chemical gilding and...

 in the presence of sodium nitrite and heat. Cyanocobalamin is not produced directly by any species of bacterium, but compounds with vitamin B12 activity can be made by many bacterial species. Since a number of species of Propionibacterium
Propionibacterium is a genus of bacteria named for their unique metabolism: They are able to synthesize propionic acid by using unusual transcarboxylase enzymes....

 produce no exotoxin
An exotoxin is a toxin excreted by a microorganism, like bacteria, fungi, algae, and protozoa. An exotoxin can cause damage to the host by destroying cells or disrupting normal cellular metabolism. They are highly potent and can cause major damage to the host...

s or endotoxin
Endotoxins are toxins associated with some Gram-negative bacteria. An "endotoxin" is a toxin that is a structural molecule of the bacteria that is recognized by the immune system.-Gram negative:...

s and are generally regarded as safe (have been granted GRAS
Gras is a commune in the Ardèche department in southern France.-Population:-References:*...

 status) by the Food and Drug Adminstration of the United States, they are presently the preferred bacterial fermentation organisms for vitamin B12 production.

Historically, a form of vitamin B12 called hydroxocobalamin
Hydroxocobalamin is a natural form, or vitamer, of vitamin B12, a basic member of the cobalamin family of compounds. Hydroxocobalamin is the form of vitamin B12 produced by many bacteria which are used to produce the vitamin commercially. Like other forms of vitamin B12, hydroxocobalamin has an...

 is often produced by bacteria, and was then changed to cyanocobalamin in the process of being purified in activated charcoal columns after being separated from the bacterial cultures. This change was not immediately realized when vitamin B12 was first being extracted for characterization. Cyanide
A cyanide is a chemical compound that contains the cyano group, -C≡N, which consists of a carbon atom triple-bonded to a nitrogen atom. Cyanides most commonly refer to salts of the anion CN−. Most cyanides are highly toxic....

 is naturally present in activated charcoal, and hydroxocobalamin, which has great affinity for cyanide, picks it up, and is changed to cyanocobalamin. Cyanocobalamin is the form in most pharmaceutical preparations because adding cyanide stabilizes the molecule.

France accounts for 80 % of world production, and more than 10 tonnes/year of this compound is sold; 55 % of sales is destined for animal feed, while the remaining 45 % is for human consumption.

Pharmaceutical use

Cyanocobalamin is usually prescribed for the following reasons: after surgical removal of part or all of the stomach or intestine to ensure there are adequate levels of vitamin B12 in the bloodstream; to treat pernicious anemia
Pernicious anemia
Pernicious anemia is one of many types of the larger family of megaloblastic anemias...

; vitamin B12 deficiency due to low intake from food; thyrotoxicosis; hemorrhage; malignancy; liver or kidney disease. Cyanocobalamin injections are often prescribed to gastric bypass patients having had part of their small intestine bypassed, making it difficult for B12 to be absorbed via food or vitamins. Cyanocobamide is also used to perform the Schilling test
Schilling test
The Schilling test is a medical investigation used for patients with vitamin B deficiency. The purpose of the test is to determine whether the patient has pernicious anemia.It is named for Robert F. Schilling.-Process:The Schilling test has multiple stages...

 to check a person's ability to absorb vitamin B12.

End Product of Cyanide Poisoning Treatment

In cases of Cyanide poisoning the patient is given hydroxocobalamin, which is a precursor to cyanocobalamin. The hydroxocobalamin binds with the cyanide ion and forms cyanocobalamin which can then be secreted by the kidneys. This has been used for many years in France and was approved by the FDA in Dec 2006, marked under the name Cynokit.

Possible side effects

The oral use of cyanocobalamin may lead to several allergic reactions such as hives; difficult breathing; swelling of the face, lips, tongue, or throat. Less-serious side effects may include headache, nausea
Nausea , is a sensation of unease and discomfort in the upper stomach with an involuntary urge to vomit. It often, but not always, precedes vomiting...

, stomach upset, diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...

, joint pain, itching, or rash
A rash is a change of the skin which affects its color, appearance or texture. A rash may be localized in one part of the body, or affect all the skin. Rashes may cause the skin to change color, itch, become warm, bumpy, chapped, dry, cracked or blistered, swell and may be painful. The causes, and...


In the treatment of some forms of anemia (e.g., megaloblastic anemia
Megaloblastic anemia
Megaloblastic anemia is an anemia that results from inhibition of DNA synthesis in red blood cell production. When DNA synthesis is impaired, the cell cycle cannot progress from the G2 growth stage to the mitosis stage...

), the use of cyanocobalamin can lead to severe hypokalemia
Hypokalemia or hypokalaemia , also hypopotassemia or hypopotassaemia , refers to the condition in which the concentration of potassium in the blood is low...

, sometimes fatal, due to intracellular potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...

 shift upon anemia resolution (but this same effect should be observed with any B12 vitamer, not just cyanocobalamin). When treated with vitamin B12, patients with Leber's disease may suffer rapid optic atrophy.

Cyanide is present in almost every type of smoke produced by burning organic materials, including tobacco
Tobacco is an agricultural product processed from the leaves of plants in the genus Nicotiana. It can be consumed, used as a pesticide and, in the form of nicotine tartrate, used in some medicines...

and cannabis; therefore, there is some concern that vitamin B12-deficient smokers should not be given cyanocobalamin, as it will have more difficulty being broken down. In such cases, other forms of vitamin B12 for injection (such as hydroxocobalamin itself) are commonly available as pharmaceuticals, and are actually the most commonly used injectable forms of vitamin B12 in many countries. Injectable cyanocobalamin remains the most commonly injectable vitamin B12 in the United States.