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.

The treated cell cultures, the agency noted, are a biological product as defined in the PHS Act, in that they are a virus, therapeutic serum, toxin, antitoxin, vaccine, blood, blood component or derivative, allergenic product or analogous product, or arsphenamine or derivative of arsphenamine, applicable to the prevention, treatment or cure of a disease or condition of human beings.

The treated cell cultures, the agency noted, are a biological product as defined in the PHS Act, in that they are a virus, therapeutic serum, toxin, antitoxin, vaccine, blood, blood component or derivative, allergenic product or analogous product, or arsphenamine or derivative of arsphenamine, applicable to the prevention, treatment or cure of a disease or condition of human beings.