Atoxyl is the name of a drug consisting of p-aminophenylarsenic acid. This organoarsenic compound was used in the late 19th and early 20th centuries, but is now considered dangerously toxic.
Béchamp optimistically chose the name Atoxyl, referring to the reduced toxicity of the resulting compound (compared to arsenic). Atoxyl was initially used in medicine to treat simple skin diseases. In 1905, two British physicians, H.W. Thomas and A. Breinl, discovered that Atoxyl was active against the trypanosomes of sleeping sickness. The effect of atoxyl was however not very pronounced, and the necessary dosage was so high that its toxic side effects far outweighed the benefits. Atoxyl frequently caused blindness by damaging the optic nerve and other varied disorders.
Nevertheless, the discovery of atoxyl's activity against trypanosomes was the basis for a major advance by the bacteriologist Paul Ehrlich. Ehrlich believed the accepted formula for atoxyl at that time was incorrect. Ehrlich and an organic chemist, Alfred Bertheim, identified the correct structural formula. The correct formula suggested new ways that the atoxyl molecule could be modified, and a series of such derivatives were then synthesized for testing. Testing for anti-syphilitic activity was performed by Sahachiro Hata who worked in Ehrlich's lab. The result of this team effort was the discovery of the drug Salvarsan in 1909.