The effect of pyrimethamine (daraprim) on the gametocytes and oocysts of Plasmodium falciparum and Plasmodium vivax

1. (1) Plasmodium vivax. When only 5 mg. or less of pyrimethamine was given, most of the oocysts developed normally and the resulting sporozoites were infective.Some, however, were drug-affected and failed to develop. When 50 mg. of pyrimethamine was given, none of the oocysts reached maturity even when the mosquitoes were fed 2 hours after the drug was given. 2. (2) Plasmodium falciparum. When 25 mg. of pyrimethamine was given, none of the oocysts reached maturity.The gametocytes were affected by the drug as early as 3 hours after treatment and as late as 144 hours. These results suggest that pyrimethamine could play an important part in severing the parasite cycle between man and mosquito.