Therapeutic Effectiveness of Certain Sulfonamides on Infection by an Intracellular Protozoon (Toxoplasma) ∗

Summary

Sulfathiazole and sulfapyridine, although without effect on toxoplasma in vitro, have been found to have a complete inhibitory and under certain conditions, curative action on toxoplasmic infection in mice when administered in 1% concentration in the diet. Sulfanilamide did not have a similar effect. Mice infected with 100 M.L.D. or less were cured when 1% sulfathiazole was given for 16 days or longer. Although mice infected intraâbdominally with a single M.L.D. had a maximum survival time of about 14 days, animals infected with 1,000 to 10,000 M.L.D. remained well as long as they were consuming the drug diet and for variable periods thereafter, but ultimately succumbed to toxoplasmic infection. It seemed remarkable that many such animals which had received the 1% sulfathiazole diet for 45 days did not succumb for 1 to 2 months after discontinuance of the drug. Sulfathiazole in the diet was equally effective when the toxoplasma were injected intraâbdominally or intracere-brally. Apparently because of the irregular eating habits of rabbits, 1% sulfathiazole in the diet was without effect on toxoplasmic infection in them. However, when large doses of sulfathiazole were administered parenter-ally at regular intervals, day and night, a distinct curative effect was obtained even when the drug was first administered 3 days after infection by the intracutaneous route, at a time when well developed local lesions and fever, indicative of a generalized systemic infection, were present. Atabrin and quinine hydrochloride which were previously found to be toxoplasmacidal in in vitro tests, were without effect on toxoplasmic infection in mice when administered in the diet.