How Does Sodium Thiosulphate Cure Cyanide Poisoning?

by Lucy Bell-Young

Sodium thiosulphate (Na2S2O3) is considered one of the most important medicines in the health system because of its ability to treat rare diseases, like pityriasis versicolour, calciphylaxis and, most famously, cyanide poisoning.

Cyanide poisoning is very rare yet very sinister. It works by depriving cells of oxygen which leads to the death of critical cells. The properties of sodium thiosulphate make it an effective treatment as it is able to convert the poisonous cyanide into the less toxic thiocyanate.

What is Cyanide?

Hydrogen cyanide was originally formed during the process of making Prussian blue pigment, and so cyanide gets its name from the Greek word kyanos, meaning dark blue.

Cyanide is a chemical compound that is comprised of a carbon-nitrogen triple bond (C≡N). Known as a cyano group, it exists as a colourless anion (CN-) in inorganic compounds like sodium cyanide, potassium cyanide and the notorious hydrogen cyanide.

These substances are all extremely toxic because they release the CN- ion. This is the component that makes cyanide dangerous as it behaves as a metabolic toxin. This is why we know cyanide as the sinister poison used in murder mysteries and genocides, but humans are actually exposed to this compound more often than you would think.

Nitriles used in pharmaceuticals, like citalopram or cimetidine, contain cyanide, as well as everyday food items like apple seeds, almonds, tapioca and spinach. When found here, the CN- ion is not readily released. Therefore, consuming cyanide in this way isn’t harmful.

Blue hued mountains
Before cyanide, there was hydrogen cyanide (HCN). HCN was first isolated from Prussian blue pigment, and for many years was referred to as ‘prussic acid’ because of this association. When cyanide was discovered two years later, it was named after the Greek word kyanos which meant dark blue.

What is Cyanide Poisoning?

Cyanide is one of the most rapid and dangerous poisons to mammals. Cyanide poisoning inhibits cells from taking up oxygen from the bloodstream. In this way, it is a form of histotoxic hypoxia. When it has been ingested, cyanide affects two main functions of the body:

  1. Cytochrome C Oxidase: this enzyme operates in the mitochondria. It is a cellular respiratory enzyme and it plays a crucial role in the life-supporting process of ATP synthesis by reducing molecular oxygen to water
  2. ATP (Adenosine Triphosphate): found in the cells of every life form, ATP is an energy-carrying molecule that captures and stores energy. It then uses this to fuel every cellular process, giving us the energy we need to do just about everything

Cyanide prevents cells and tissue from using oxygen by inhibiting cytochrome c oxidase. When the compound is ingested, several things happen in the space of a few seconds:

  • Cyanide is attracted to the iron atom in cytochrome oxidase
  • This attraction causes it to bind to cytochrome c oxidase in the mitochondria of the cells
  • The presence of cyanide interrupts the electron transport along cytochrome c oxidase and it begins to behave as an irreversible enzyme inhibitor
  • The blocked electron transfer halts oxidative metabolism, cellular respiration and the production of ATP
  • Oxyhemoglobin also can’t release its oxygen for electron transport
  • All of this leads to the appearance of bright red, oxygenated blood since cells are unable to take the oxygen from it
  • This induces cytotoxic anoxia because the brain can’t absorb oxygen, and also histotoxic hypoxia because the cells can’t utilise oxygen from the blood
  • Without the energy produced by ATP, tissues like the heart muscle cells and nerve cells quickly expend their energy and die
  • This results in a large death rate of critical cells, which the body can’t live without. In the central nervous system, the inhibition of oxidative metabolism could also lead to respiratory arrest and death

One of the first symptoms of cyanide poisoning is a rapid increase in the rate and depth of breathing. Inhaling a high dose of cyanide will result in unconsciousness followed by death, and this can happen in the space of a few minutes. Inhaling a low dose is survivable if treated immediately.

Pharmaceuticals often contain cyanide but won't give you Cyanide poisoning
Nitriles used in pharmaceuticals often contain cyanide. However, they don’t readily release the toxic CN- ion and so when consumed like this the cyanide isn’t harmful.

How Does Sodium Thiosulphate Cure Cyanide Poisoning?

Sodium thiosulphate exerts its antidotal effect by acting as sulphur-donating agent. This sulphur transferase allows it to combine with cyanide to form thiocyanate, a substance that is 200 times less toxic than cyanide. The mechanism of sodium thiosulphate action is as follows:

  • The mitochondrial enzyme rhodanese, also known as thiosulphate sulphurtransferase, referees the transfer of sulphur from sodium thiosulphate to the cyanide ion
  • Sodium thiosulphate (Na2S2O3) donates a sulphur atom to cyanide (CN-) and forms the anion thiocyanate (SCN-)
  • Cyanide is then released in the presence of methemoglobin, which helps to form cyanomethemoglobin
  • The formation of cyanomethemoglobin prevents free cyanide from binding to cytochrome c oxidase
  • This results in the reactivation of cytochrome c oxidase activity and ATP production, the release of respiratory enzymes and the restoration of cell respiration
  • Cyanide-containing thiocyanate is then excreted from the body in urine

Although cyanide poisoning is rare, cyanide is a very common toxin in the environment and we actually consume small traces of it every day. Since we already have low concentrations of sodium thiosulphate in our body, the detoxification process above occurs naturally.

However, our body’s system of detoxifying itself is limited because of the low availability of sodium thiosulphate. When large doses of cyanide are ingested, the rhodanese mechanism of converting CN- into thiocyanate is incapable of handling all the cyanide being released, allowing it to reach toxic concentrations.

This is why sodium thiosulphate is so important in the health system; it is one of the only treatments that can be used as an antidote for cyanide poisoning.

A science model showing the human anatomy
Cyanide is everywhere. For example, it is in apple seeds, tapioca, spinach and more. The body can detoxify itself when this happens, but not when any higher amount of cyanide is ingested.

At ReAgent, sodium thiosulphate is available in 1kg containers, and you can even get great discounts when you buy in bulk. You can buy this product in 0.01M and 0.1M solutions, and you can buy with confidence knowing that all of our products are backed by a 100% quality guarantee. Shop online today or call a member of our team for more information.


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