Despite its known unhealthy, or even lethal characteristics, arsenic is a common ingredience in several medical prescriptions through time, and, apart from his bad reputation, often quite helpful.
I still remember wondering about the usage of arsenic in a prescription for hurting fingernails, which I read when I was eleven. The book was printed in 1731, and I loved to read through all the oddities it contained. The prescription explaines how to remove a fingernail without pain, and make it grow again:
Take gummi serapinum [Sagapenum], arsenic, both of the same quantity, powdered, and then make it with nut oil to a cream, put it on a fine cloth, and place all on the fingernail. The fingernail then can be removed without pain, then take a cold lye, and wash your toes or fingers with it.
Arsenic, apart generally causing cancer when exposed to it, also has positive effects on cancer, e.g. when directly applied on the carcinoma (already noted by H. Simon, Die Behandlung der Geschwülste, Berlin 1914) – but not only. It it also used to treat a type of acute myeloid leukaemia called acute promyelocytic leukaemia (see here), and shows good promises in cancer treatment.
One of the earlier medicines against syphilis was made of arsenic and showed far less negative side effects than the previously used mercury (with severe side effects such as neuropathies, kidney failure, and severe mouth ulcers and loss of teeth). Arsphenamine (or Salvarsan / compound 606) was first synthesised in 1907 by P. Ehrlich and S. Hata and widely used (see also the “magic bullet“). The administration of treatment was complex requiring many injections over a long period of time, and it also produced toxic side effects, which were reduced by combining it with small doses of bismuth and mercury.
In the beginning of the 1940s, the arsenical compounds were supplanted as treatments for syphilis by penicillin. Not so in Eastern Germany; after the 2WW, the number of syphilis-infections rose dramatically, and Salvarsan or Neo-Salvarsan were not available. E. Schmitz (Magdeburg) managed to synthesise Neo-Salvarsan, which was sold as Arsaminol and later Neo-Arsoluin, and still contained arsenic; consequently, also syphilis infections dropped significantly in Eastern Germany.