THE RÔLE OF MOLECULAR OXYGEN IN THE ANTISPIROCHETAL ACTIVITY OF ARSENIC AND BISMUTH COMPOUNDS IN VITRO

¹ From the United States Public Health Service, Washington, and the Syphilis Division of the Department of Medicine, Johns Hopkins Medical School, Baltimore

The antispirochetal action in vitro of "arsenoxide" (m-amino-p-hydroxyphenylarsenoxide) and bismuth compounds is unaffected by the removal of molecular oxygen, and is probably due to these compounds as such. In marked contrast, neoarsphenamine, which is highly spirocheticidal when dissolved aerobically, is negligibly so when dissolved and tested under nitrogen in the absence of oxygen. Its relatively marked antispirochetal action when tested aerobically (25 to 60 times that observed under nitrogen) is apparently due to its oxidation by molecular oxygen to other directly spirocheticidal compounds. This oxidation does not require the presence of tissue derivatives and proceeds so rapidly that solutions become actively spirocheticidal within 3 to 5 minutes. Commercial neoarsphenamine does not contain significant amounts of "arsenoxide," or substances which, like "arsenoxide," are directly spirocheticidal.

Commercial arsphenamine and silver arsphenamine are intermediate between "arsenoxide" and neoarsphenamine, in that although two-thirds to seven-eighths of their antispirochetal activity in vitro is due to oxidation products, there is a small but significant residual activity in the absence of oxygen. In the case of arsphenamine, a large part of this residual activity is accounted for by "arsenoxide" or "arsenoxide"-like substances present as an impurity.