The action of 2:4-diamino-6:7-diisopropylpteridine on normal, proguanil- and sulphadiazine-resistant strains of Plasmodium gallinaceum

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

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.

The chemotherapy of Plasmodium berghei. II. Antagonism of the action of drugs

The action of pyrimethamine, sulphadiazine, proguanil and its active metabolite CPT, and 2:4-diaminopteridines against infections ofPlasmodium bergheiin mice was antagonized byP–aminobenzoic acid and by pteroylglutamic acid. Antagonism was in some instances detected only whenP–aminobenzoic acid was given in solution in the drinking water as well as being injected subcutaneously. No antagonism was detected with a number of amino acids and nucleic acid derivatives.

As all of the above group of drugs can be antagonized byP–aminobenzoic acid and by pteroylglutamic acid, it would seem that they are alike in their mode of action. There must, however, be some differences between the mode of action or absorption of these drugs because species ofPlasmodiumthat are very sensitive to the action of one of these drugs are frequently not very sensitive to the action of others.

AsP. bergheiis dependent onp–aminobenzoic acid, it is suggested that it can utilize this compound in the synthesis of pteroylglutamic acid to a greater extent than canP. gallinaceum, and that it resemblesP. knowlesimore than other species ofPlasmodium.

The chemotherapy of Plasmodium berghei. I. Resistance to drugs

1. Strains of P. berghei resistant to sulphadiazine, pyrimethamine, and methylene blue were produced by treating acute infections with low doses of drug.

2. The strain resistant to methylene blue was sensitive to pamaquin, mepacrine, sulphadiazine, proguanil, pyrimethamine, and 2 : 4-diamino-6 : 7-camphano-pteridine.

3. The pyrimethamine-resistant strain was cross-resistant to proguanil and its active metabolite CPT, 2 : 4-diamino-6 : 7-camphanopteridine, 2 : 4-diamino-6 : 7-(l′-ethylindolo)-pteridine, and 2 : 4-diamino-5-p-chlorophenylpyrimidine.

4. The sulphadiazine-resistant strain was cross-resistant to pyrimethamine, sulphanilamide, proguanil and its active metabolite CPT, 2 : 4-diamino-6 : 7-dinhexylpteridine, and 2 : 4-diamino-6 : 7-diisopropylpteridine. It was as sensitive as the parent strain to quinine, mepacrine, chloroquin, pamaquin, methylene blue, and M 3349.

5. The action of sulphadiazine against the sulphadiazine-resistant strain was inhibited by the same doses of p-aminobenzoic acid and folic acid as were required with the parent strain, although the dose of sulphadiazine was increased 30-fold.