Cyanide

A cyanide is any chemical compound that contains the group C≡N, with the carbon atom triple bonded to the nitrogen atom. Inorganic cyanides contain the highly toxic cyanide ion CN- and are the salts of the acid hydrogen cyanide (HCN). Organic cyanides contain the cyano group (CN) single-bonded to another carbon atom are also known as nitriles. Two cyanide ions can bond to each other via their carbon atoms, forming the gas cyanogen (NC-CN).

Mechanism of toxicity and treatment

The cyanide ion kills all aerobic organisms by shutting down the respiration in cells. It interrupts the electron transport chain in the inner membrane of the mitochondrion because it binds more strongly than oxygen to the Fe3+ (ferric iron ion) in cytochrome a3, preventing this cytochrome from combining electrons with oxygen.

Related Topics:
Aerobic organism - Respiration - Electron transport chain - Membrane - Mitochondrion - Oxygen - Fe - Cytochrome a₃ - Cytochrome - Electron

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Contrary to popular belief, cyanide does not bind well to ferrous hemoproteins, such as hemoglobin, the mechanism which makes carbon monoxide toxic. One of the therapies for cyanide poisoning is to convert part of the hemoglobin of the blood from ferrous (2+ charge) hemoglobin to ferric (3+ charge); this creates a pool of binding potential that can divert cyanide from the cytochromes it poisons. This is done with the compound 4-dimethylaminophenyl (4-DMAP), or with sodium nitrite.

Related Topics:
Ferrous - Hemoprotein - Hemoglobin - Carbon monoxide - Blood - Ferric - 4-dimethylaminophenyl (4-DMAP) - Sodium nitrite

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The United States standard cyanide antidote kit uses a small inhaled dose of amyl nitrite followed by intravenous sodium nitrite. This converts a portion of the hemoglobin's iron from ferrous iron to ferric iron, converting the hemoglobin into methemoglobin. Cyanide is more strongly drawn to methemoglobin than to the cytochrome oxidase of the cells, effectively pulling the cyanide off the cells and onto the methemoglobin. Once bound with the cyanide, the methemoglobin becomes cyanmethemoglobin. Therapy with nitrites is not innocuous. The doses given to an adult can potentially cause a fatal methemoglobinemia in children or may cause profound hypotension. Treatment of children affected with cyanide intoxication must be individualized and is based upon their body weight and hemoglobin concentration. The next part of the cyanide antidote kit is sodium thiosulfate, which is administered intravenously. The sodium thiosulfate and cyanmethemoglobin become thiocyanate, releasing the hemoglobin, and the thiocyanate is excreted by the kidneys.

Related Topics:
United States - Antidote - Amyl nitrite - Ferrous - Ferric - Methemoglobin - Oxidase - Methemoglobinemia - Sodium thiosulfate - Thiocyanate

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Alternative methods of treating cyanide intoxication are used in other countries. For example, France uses hydroxycobalamin (a form of vitamin B12), which combines with cyanide to form the harmless vitamin B12a cyanocobalamin. Cyanocobalamin is eliminated through the urine. Hydroxycobalamin works both within the intravascular space and within the cells to combat cyanide intoxication. This contrasts with methemoglobin which only acts within the vascular space as an antidote. Administration of sodium thiosulfate improves the ability of the hydroxycobalamin to detoxify cyanide poisoning. This treatment is considered so effective and innocuous that it is administered routinely in Paris to victims of smoke inhalation to detoxify any associated cyanide intoxication. However it is relatively expensive and not universally available.

Related Topics:
Vitamin B₁₂ - Sodium thiosulfate

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4-Dimethylaminophenol (4-DMAP) has been proposed in Germany as a more rapid antidote than nitrites and with (reportedly) lower toxicity. It is used currently by the German military and by the civilian population. In humans, intravenous injection of 3 mg/kg of 4-DMAP will produce 15% methemoglobin levels within 1 minute.

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Cobalt salts have also been demonstrated as effective in binding cyanide. One current cobalt-based antidote available in Europe is dicobalt-EDTA, sold as Kelocyanor®. This agent chelates cyanide as the cobalticyanide. This drug provides an antidote effect more quickly than formation of methemoglobin but a clear superiority to methemoglobin formation has not been demonstrated. Cobalt complexes are quite toxic, and there have been accidents reported in the UK where patients have been given dicobalt-EDTA by mistake based on a false diagnosis of cyanide poisoning.

Related Topics:
Cobalt - Salt - Complexes - UK

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