Sodium thiosulfate, or sodium thiosulphate, is a colorless, water-soluble salt. It is a calcium-chelating agent and has many medical uses in removing toxic substances from the body. Depending on the medical condition being treated, the salt can be injected, taken orally, or applied to the skin. It is also used in some vital tests for kidney patients to glean information without doing harm.

This compound is combined with sodium nitrite and used as an antidote for cyanide poisoning in both children and adults. Sodium thiosulfate reacts with the cyanide and forms sodium thioyanate, a nontoxic substance that can then be excreted harmlessly from the body. The salt is also used to treat arsenic poisoning. Studies show that it can be useful in removing excess copper from patients too.
The calcium-chelating properties of sodium thiosulfate make it a useful agent for treating disorders involving excess calcium. Both tumoral calcinosis and calcific nephrolithiasis have been successfully treated with the salt. Studies indicate it may treat calciphylaxis, a condition that sometimes occurs in chronic kidney dialysis patients.

Ringworm and tinea versicolor are fungal infections of the skin. Ringworm looks like a circular area of rash, while tinea versicolor appears as white patches on the skin. Sodium thiosulfate is used to treat both of these fungal infections. It is added to the water of footbaths to treat ringworm of the feet. To treat tinea versicolor, the salt is often combined with salicylic acid in a preparation that is applied topically to the affected areas.
Medical Summary
*It is used as an antidote to cyanide poisoning.Thiosulfate acts as a sulfur donor for the conversion of cyanide to thiocyanate (which can then be safely excreted in the urine), catalyzed by the enzyme rhodanase.
*It has also been used as treatment of calciphylaxis in hemodialysis patients with end-stage renal disease.
*It is used in the management of extravasations during chemotherapy. Sodium thiosulfate prevents alkylation and tissue destruction by providing a substrate for the alkylating agents that have invaded the subcutaneous tissues. The dose may be 2mL of 0.17M (a solution of 4mL 10% sodium thiosulfate and 6mL sterile water for injection). It may be instilled subcutaneously into multiple sites using a small gauge needle. There are limited data on this method with few recommendations.
*in foot baths for prophylaxis of ringworm, and as a topical antifungal agent for tinea versicolor.
*in measuring the volume of extracellular body fluid and the renal glomerular filtration rate.
Other Uses
Sodium thiosulfate has many uses ,some main uses are as follows:
1. In analytical chemistry, the most important use comes from the fact that the thiosulfate anion reacts stoichiometrically with iodine, reducing it to iodide as it is oxidized to tetrathionate:
                                     2 S2O32-(aq) + I2(aq) → S4O62-(aq) + 2 I-(aq)
Due to the quantitative nature of this reaction, as well as the fact that Na2S2O3.5H2O has an excellent shelf-life, it is used as a titrant in iodometry. Na2S2O3.5H2O is also a component of iodine clock experiments.
2. Sodium thiosulfate is one component of an alternative lixiviant to cyanide for extraction of gold. It forms a strong complex with gold(I) ions, [Au(S2O3)2]3-.