QUANTITATIVE STUDIES IN CHEMOTHERAPY IV. THE RELATIVE THERAPEUTIC VALUE OF ARSPHENAMINE AND NEOARSPHENAMINE OF DIFFERENT MANUFACTURE

¹ From the Division of Pharmacology, Hygienic Laboratory, United States Public Health Service

1. Six different brands of arsphenamine, including a German preparation, have shown approximately the same trypanocidal activity.

2. Slightly greater variations in activity were observed with six different samples of neoarsphenamine, the maximum difference being 80 per cent.

3. There appears to exist no relation between toxicity and trypanocidal action of arsphenamine and neoarsphenamine.

4. It is suggested that the alleged greater effectiveness of arsphenamine over neoarsphenamine in the treatment of human syphilis may be attributed to the fact that arsphenamine is precipitated at the hydroxyl ion concentration of the blood, in consequence of which the rate of its oxidation and elimination from the body is considerably diminished.

5. The study of the trypanocidal action of some aliphatic arsenicals has confirmed the fundamental principle formulated from the previous study of the aromatic arsenicals, viz., that the trivalent oxides are the only forms of arsenic which exert a direct toxic action upon protoplasm.

6. Cacodylic acid does not possess any trypanocidal action even in lethal doses. Methyl and ethyl arsenic acid show a parasitocidal action only when used in doses approaching the lethal dose.