Vitamin B12 as an Antidote to Cyanide Poisoning

Vitamin B12 (cobalamin) plays an important role in human health. By definition we cannot live without it, and we cannot make it ourselves, so we traditionally obtained it through the diet. A lack of vitamin B12, or the inability to absorb it from our food results in problems with DNA synthesis. This manifests itself first as anemia, and if the lack of B12 is not remedied, symptoms will develop that are more serious, like balance problems, seizures, paralysis and dementia, eventually resulting in death. The type of anemia traditionally associated with vitamin B12 deficiency is pernicious anemia. People with pernicious anemia can no longer absorb the vitamin from food, so they need to take supplements either through injections, transdermal patches, or sublingually. Those routes of administration bypass the gastrointestinal tract and allow the vitamin to be absorbed directly into the bloodstream. However, if oral supplements are taken that are concentrated enough, like several milligrams per dose, enough vitamin can be passively absorbed through the whole small intestine, as long as enough length of intestine is available. Persons who have had part of their small intestine removed or bypassed through surgery would probably be good candidates for injections. A few micrograms a day of cobalamin will stave off deficiency symptoms and even reverse some of the cognitive deficits if they have not progressed too far.

The cobalamin molecule has a strong affinity for the cyanide ion (CN^-). So strong in fact, that during the extraction of the vitamin from bacterial sources, it becomes attached to environmental cyanide, and is obtained as cyanocobalamin. Most multivitamin supplements that contain vitamin B12 have it in this form. When we take cyanocobalamin, very small amounts of cyanide get released into the body. This is normally not a problem, as we are equipped to neutralize small quantities of this toxin. Cyanide-releasing chemicals are found in small amounts in some foods also.

An important source of acute cyanide toxicity is smoke inhalation from fires. The burning of wood, plastics and other substances produces hydrogen cyanide gas (HCN), which is in the volatile portion of smoke. When smoke is inhaled in a fire, the hydrogen cyanide releases cyanide ion in the bloodstream and an overwhelming amount of cyanide enters the cells. In our cells the organelles responsible for energy production are the mitochondria. One mitochondrial enzyme, cytochrome C oxidase, unfortunately also has an affinity for cyanide. It normally reacts with oxygen. Cyanide poisoning occurs when cyanide binds to cytochrome C oxidase, and inhibits its action. Cytochrome c oxidase participates in a series of metabolic pathways known as cellular respiration. When this enzyme is inactivated by cyanide, mitochondrial adenosine triphosphate (ATP) production comes to a halt. Since ATP is used to power most cellular reactions, cyanide poisoning will kill quickly. A person who dies from lack of oxygen is asphyxiated. Cyanide causes asphyxiation because it interrupts the reactions that allow a cell to make ATP in the presence of oxygen (aerobic cellular respiration). Even if oxygen is there, we cannot use it if cyanide is present also.

The natural affinity of the cobalamin molecule for cyanide can be used to extract cyanide from the cells. For this another form of cobalamin is used, hydroxocobalamin (also called hydroxycobalamin). When hydroxocobalamin reaches a cytochrome C oxidase enzyme that has cyanide attached to it, it pulls the cyanide from the cytochrome C oxidase. This restores the enzyme's activity and forms cyanocobalamin. As you know, cyanocobalamin is not toxic, and the excess is harmlessly excreted in the urine.

Paramedics administer hydroxocobalamin at the scene of a fire, as soon as the victim has been rescued by fire fighters. Even though fire fighters wear special masks and filters to protect them, cyanide poisoning from smoke inhalation is one of their occupational hazards. The dose of hydroxocobalamin needed to flush the cyanide out of the body is phenomenal. Five grams of the vitamin (many times the estimated amount needed over a human lifetime and 1000 times the dose of a 5 mg supplement) are injected over 15 minutes. This first dose may be followed with more. The therapy starts at the scene and continues in the ambulance and in the hospital. The quicker the cyanide is removed, the less chance for permanent cognitive deficits.

A person who habitually inhales tobacco smoke by smoking or through second-hand smoke gets a chronic low-level exposure to cyanide from the combustion products of the tobacco from cigarettes.  Smoking cigars, pipes or pot also has this same effect.  You could say it's a recreational hazard.  One good thing to do to counteract low levels of cyanide toxicity is to take vitamin B12 in the hydroxycobalamin form.  Cyanocobalamin would not be indicated for this purpose as it already would be bringing cyanide into the body.  Remember, most supplements contain cyanocobalamin, so check the label.