The action of 2:4-diamino-6:7-diisopropylpteridine upon Plasmodium gallinaceum and its relation to other compounds which are pteroylglutamic acid antagonists.

Abstract

1. Two strains ofPlasmodium gallinaceumwere 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 ofP. gallinaceummade resistant to 0/63 was resistant to proguanil, pyrimethamine and 0/129, but not to sulphadiazine.5. The action of 0/129 and proguanil uponP. gallinaceumwas not antagonized byp–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 uponP. gallinaceumwas antagonized competitively byp–A.B., it was antagonized by P.G.A. only when the sulphadiazine was given in small doses.