The Relative Activity of the Common Sulfonamides against Experimental Toxoplasmosis in the Mouse

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Abstract
Summary Defining the effective dose as the dose producing 10-day survival of mice inoculated with 20,000 Toxoplasma organisms, median effective doses of the common sulfonamides were measured under uniform conditions, as follows: Sulfadiazine 0.040 per cent in the diet Sulfamerazine 0.039 per cent in the diet Sulfamethazine 0.036 per cent in the diet Sulfathiazole 0.190 per cent in the diet Sulfapyridine 0.450 per cent in the diet Sulfanilamide 0.600 per cent in the diet Since the pyrimidine derivatives, sulfadiazine, sulfamerazine and sulfamethazine, had the smallest effective dosages and are known to be the least toxic of the sulfonamides tested, it was concluded that these drugs are the most efficient antitoxoplasmic agents. Although MED's were low, increasing the amount of drug administered did not result in all animals surviving. With the highest dosages only about two-thirds survived 10 days. Blood chemistry studies showed that sulfadiazine, sulfamerazine, and sulfamethazine are effective in mice at blood levels much below those safely attainable in man. About one-fourth of the mice given a dosage of 0.063 per cent or more sulfadiazine in the diet survived for 42 days. A number of these animals were tested to see if cure (freedom from parasites) had been effected. In the majority of cases tissues from the surviving mice produced no infection when injected into clean recipient mice. Other surviving animals were reinoculated with Toxoplasma organisms and all of these proved susceptible and most died from five to seven days later.