Dimercaprol

Dimercaprol (INN) or British anti-Lewisite (abbreviated BAL), is a compound developed by British biochemists at Oxford University during World War II. It was developed secretly as an antidote for Lewisite, the now-obsolete arsenic-based chemical warfare agent. Today, it is used medically in treatment of arsenic, mercury and lead, and other heavy metal poisoning. In addition, it is used for the treatment of Wilson's disease, a genetic disorder in which the body tends to retain copper.

Biochemical function
Heavy metals act by chemically reacting with adjacent sulfhydryl residues on metabolic enzymes, creating a chelate complex that inhibits the affected enzyme's activity. Dimercaprol competes with the sulfhydryl groups for binding the metal ion, which is then excreted in the urine.

Dimercaprol is itself toxic, with a narrow therapeutic range and a tendency to concentrate arsenic in some organs. Other drawbacks include the need to administer it by painful intramuscular injection.

BAL has been found to form stable chelates in vivo with many toxic metals including inorganic mercury, antimony, bismuth, cadmium, chromium, cobalt, gold, and nickel. However, it is not necessarily the treatment of choice for toxicity to these metals. BAL has been used as an adjunct in the treatment of the acute encephalopathy of lead toxicity. It is a potentially toxic drug, and its use may be accompanied by multiple side effects. Although treatment with BAL will increase the excretion of cadmium, there is a concomitant increase in renal cadmium concentration, so that its use in case of cadmium toxicity is to be avoided. It does, however, remove inorganic mercury from the kidneys; but is not useful in the treatment of alkylmercury or phenyl mercury toxicity. BAL also enhances the toxicity of selenium and tellurium, so it is not to be used to remove these metals from the body.