Penicillamine is a pharmaceutical of the chelator class. The pharmaceutical form is D-penicillamine, as L-penicillamine is toxic (it inhibits the action of pyridoxine). It is an α-amino acid metabolite of penicillin, although it has no antibiotic properties. Penicillamine is used as a form of immunosuppression to treat rheumatoid arthritis. It works by reducing numbers of T-lymphocytes, inhibiting macrophage function, decreasing IL-1, decreasing rheumatoid factor, and preventing collagen from cross-linking. Penicillamine has been used to treat scleroderma. Penicillamine was the second line treatment for arsenic poisoning, after dimercaprol (BAL). Bone marrow suppression, dysgeusia, anorexia, vomiting and diarrhea are the most common side effects, occurring in ~20-30% of the patients treated with penicillamine. Besides, people allergic to penicillin may have hypersensitivity to penicillamine.