Because both of these arsenicals carried considerable risk of side effects, they were replaced for this indication by penicillin in the 1940s.

Both Salvarsan and Neosalvarsan were developed in the laboratory of Paul Ehrlich in Frankfurt, Germany.

Their discoveries were the result of the first organized team effort to optimize the biological activity of a lead compound through systematic chemical modifications.

Both Salvarsan and Neosalvarsan are prodrugs – that is, they are metabolised into the active drug in the body.

[2] Presumably, Neosalvarsan also exists as a mixture of differently sized rings with arsenic-arsenic single bonds.