In vitro Investigations on the Action of Pyrimethamine against Toxoplasma gondii

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Abstract
Exposures of 4 days to a concentration of 025 gamma per ml of pyrimethamine cleared tissue cultures of monkey kidney epithelial cells of proliferating RH strain toxoplasmas. The drug had no effect on non-proliferating toxoplasmas or on the ability of Toxoplasma to enter tissue culture cells. Even after 1.5 hours'' exposure of the tissue culture cells to 0.5 mg% pyrimethamine, conditions within the cell were not favorable for the growth of toxoplasmas and prolonged incubation of the cultures so treated showed eventual clearing of parasites. No morphologic evidence of cell damage was evident when the drug was used in concentrations of 0.5 mg% for 1 week. The age of the host cell had no effect on the ability of the drug to clear tissue cultures of the parasites and treatment could be delayed for 48 hours after infection and still be effective in clearing the cultures of the parasite. The synergistic effect of pyrimethamine and sulfadiazine against T. gondii was confirmed in vitro.