Cyanocobalamin

Cyanocobalamin is an especially common vitamer of the vitamin B12 family. 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. A form of vitamin B12 called hydroxocobalamin is produced by bacteria, and then changed to cyanocobalamin in the process of being purified in activated charcoal columns after being separated from the bacterial cultures. Cyanide is naturally present in activated charcoal, and hydroxocobalamin, which has great affinity for cyanide, picks it up, and is changed to cyanocobalamin. Thus, the cyanocobalamin form of B12 is the most widespread in the food industry. .

This fact has caused some people (usually from reading labels on packages and vitamin supplements, in which vitamin B12 is almost always listed last, since ingredients by law are listed in order of weight percentage), to infer that the correct chemical name of vitamin B12 actually is cyanocobalamin. In fact, 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.

Cyanide is present in almost every type of smoke produced by burning organic materials, including tobacco 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.

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.

Production
Due to the long synthetic route, this compound is better synthesized by 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 in the presence of sodium nitrite and heat.

France accounts for 80 % of world production, and more than 10 tonnes/year of this compound is sold per year; 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; 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 to check a person's ability to absorb vitamin B12.

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, stomach upset, diarrhea, joint pain, itching, or rash.

In the treatment of some forms of anemia (e.g., megaloblastic anemia), the use of cyanocobalamin can lead to severe hypokalemia, sometimes fatal, due to intracellular potassium 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.