One of the early chemicals developed by Ehrlich which was both remarkably nontoxic to humans and remarkably toxic against a number of treponemal diseases (including syphilis and yaws) was the arsenical compound, Salvarsan arsphenamine
, which was also called the "magic bullet".
The amount of silver needed to cause argyria is not known, but studies using silver to treat syphilis in the preantibiotic era showed a link between argyria and a cumulative dose of intravenous silver arsphenamine
that exceeded 4 g intravenously.
Biological products are specific types of drugs, defined to include "a virus, therapeutic serum, toxin, antitoxin, vaccine, blood, blood component or derivative, allergenic product, or analogous product, or arsphenamine
or derivative of arsphenamine
(or any other trivalent organic arsenic compound), applicable to the prevention, treatment, or cure of a disease or condition of human beings.