The action of 2:4-diamino-6:7-diisopropylpteridine uponPlasmodium gallinaceumand its relation to other compounds which are pteroylglutamic acid antagonists

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Abstract
1. Two strains of Plasmodium gallinaceum were made resistant to 2:4-diamino-6:7-diisopropylpteridine (0/129) by treatment with that drug.2. The 0/129-resistant strains were resistant to proguanil, pyrimethamine, 2:4-diamino-6:7-diphenylpteridine (0/63) and 2:4-diamino-5-(p–chlorophenoxy)-6-methylpyrimidine (48–210), but not to sulphadiazine.3. In one strain treated with 0/129, the development of resistance to that drug itself preceded resistance to proguanil, and resistance to proguanil preceded resis tance to pyrimethamine.4. A strain of P. gallinaceum made resistant to 0/63 was resistant to proguanil, pyrimethamine and 0/129, but not to sulphadiazine.5. The action of 0/129 and proguanil upon P. gallinaceum was not antagonized by p–A.B., though in the minimum effective dose their action was antagonized by relatively large doses of P.G.A.6. Whereas the action of sulphadiazine upon P. gallinaceum was antagonized competitively by p–A.B., it was antagonized by P.G.A. only when the sulphadiazine was given in small doses.