One of the CHELATING AGENTS. It is sometimes used in RHEUMATOID ARTHRITIS that has not responded to first-line remedies, and it is particularly useful when the disease is complicated by VASCULITIS. Penicillamine is also used as an antidote to poisoning by heavy metals, particularly copper and lead, as it is able to bind these metals and so remove their toxic effects. Because of its ability to bind copper it is also used in WILSON'S DISEASE where there is a deficiency in the copper-binding protein so that copper may be deposited in the brain and liver, damaging these tissues.