THE ANTIMALARIAL ACTION IN DUCKS OF CERTAIN STJLFANILAMIDE DERIVATIVES’

In a previous publication (1) it was shown that various sulfanilamides are very effective in suppressing parasitemia in lophurae malaria of ducks; that optimal therapy depends upon the maintenance of more or less constant blood concen-trations of these drugs; and, finally, that p-aminobenzoic acid has an antagonistic effect on sufanilamides in P. lophurae as has been reported by Seeler and his associates (2) and by Maier and Riley (3) for P. gallinaceum. The complete inactivity, reported by other investigators, of sulfanilamides against relictum and cathemerium malaria in the canary was considered by us as possibly due not only to species differences in parasite susceptibility but also to the use of single daily doses of these drugs instead of the maintenance of continuous blood concentrations. In the present communication data are presented to show 1) that the maximum reduction of parasitemia that can be obtained on the sixth day with the sulfa-nilamides is a reduction from 70 per cent to 1 to 2 per cent cells parasitized and elevation of drug dosage beyond this point yields no further drop in para.sitemia,2 2) that the sulfanilamides act much more slowly than quinine in lophurae malaria in ducks, 3) that the sulfanilamides in general clinical use are much more active in lophurae than in cathemerium malaria in the duck, and 4) that certain halogen substituted sulfanilanilides appear to differ from other sulfanilamides in their mode of action. METHODS. These were in the main similar to those described in our previous communi-cation (1). For the lophurae infection, the dose of infected blood was 100 X 10 parasitized cells per bird, giving a peak of parasitemia on the sixth day, except that in certain experi-ments the dose was decreased to give a peak on the tenth day. For the cathemerium infec-tion a dose of 50 X 10 parasitized cells per bird was used and this gave a peak on the fourth or fifth day.3 White Pekin ducklings, two weeks old, and weighing about 100 grams were 1 This investigation was done under a contract recommended by the Committee o