Melarsoprol is an organoarsenic compound that was used for the treatment of sleeping sickness (African trypanosomiasis) since 1949. Melarsoprol is used for the treatment of second-stage infection (involving the central nervous system). It is the only available therapy for second-stage Trypanosoma brucei rhodesiense (East African) infection. Melarsoprol is a prodrug, upon administration it is metabolized to the active form melarsen oxide, which acts by interacting with protein sulfhydryl groups and subsequently inactivating enzymes. A small but adequate amount of the drug penetrates the cerebrospinal fluid, where it is taken up and concentrated by trypanosomes. Due to the high toxicity of the drug, it is administered only in the most dangerous cases. Melarsoprol is not commercially available in the USA, but it is available as treatment IND from CDC.