Prussian blue (medical use)

Prussian blue, also known as potassium ferric hexacyanoferrate, is used as a medication to treat thallium poisoning or radioactive caesium poisoning. For thallium it may be used in addition to gastric lavage, activated charcoal, forced diuresis, and hemodialysis. It is given by mouth or nasogastric tube. Prussian blue is also used in the urine to test for G6PD deficiency.

Side effects may include constipation, low blood potassium, and stools that are dark. With long-term use, sweat may turn blue. It mainly works by trapping the toxic monovalent cations in its crystal lattice after ion-exchange with potassium or ammonium cations and thus preventing the absorption of thallium and radio-caesium from the intestines.

Prussian blue was developed around 1706. It is on the World Health Organization's List of Essential Medicines. As of 2016, it is only approved for medical use in Germany, the United States, and Japan. Access to medical-grade Prussian blue can be difficult in many areas of the world including the developed world.