Further Studies on Cross-Resistance between Pyrimethamine and Related Compounds

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  • National Institutes of Health, National Microbiological Institute Laboratory of Tropical Diseases, Bethesda 14, Maryland


A strain of Plasmodium gallinaceum was made 800-fold resistant to pyrimethamine. The strain was found to be resistant to several other 2,4-diaminopyrimidines, chlorguanide, and a diaminotriazine at the highest dose tolerated by the chicks. These data are compared with those obtained earlier when the strain was only 64-fold resistant to pyrimethamine and these differences are discussed.