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

Absence of potentiation between quinine and pyrimethamine in infections of Plasmodium gallinaceum in chicks

The effect of combined doses of pyrimethamine and quinine has been studied in P. gallinaceum. No potentiation of the action of the drugs was observed.

Resistance to diamino-diphenylsulphone in Plasmodium gallinaceum

A fourfold enhancement of resistance to diamino-diphenylsulphone has been produced over a period of 15 months in strain A of P. gallinaceum by subjecting the strain, maintained in a state of patent infection, to increasing doses of the drug.

The DDS-resistant strain was cross-resistant to the minimum effective dose of sulphadiazine and slightly resistant to twice this dose, but it showed only a slight enhancement of resistance to pyrimethamine and proguanil.

The antimalarial action of DDS was antagonized by p–A.B. in the ratio of 100 to 1. DDS, in the minimum effective dose, was antagonized completely by folic acid if given in equal doses, but not by smaller doses of the antagonist; the antagonism was not competitive.

The relationship of cross-resistance between p–A.B.-inhibited sulphonamides and proguanil and pyrimethamine is discussed.

POTENTIATION OF SULPHADIMIDINE BY 2,4-DIAMINO-6,7-DI-ISOPROPYLPTERIDINE AND OTHER 6,7-DISUBSTITUTED 2,4-DIAMINOPTERIDINES AGAINST EIMERIA INFECTIONS OF CHICKS

Six 2,4-diaminopteridines substituted in the 6 and 7 positions were tested as potentiators of sulphadimidine against Eimeria tenella. 2,4-Diamino-6,7-di-isopropylpteridine and 2,4-diamino-1'-propylindolo(2',3':6,7)pteridine were selected for further study. Both potentiated sulphadimidine against E. tenella and the di-isopropylpteridine potentiated it against E. necatrix. A 10% mixture of the di-isopropylpteridine with sulphadimidine (or other sulphonamides) appears to offer advantages in the treatment of E. tenella and still more of E. necatrix.