Response of Sulfapyridine-fast Pneumococci to Sulfathiazole and Sulfamethylthiazole

Abstract

Our experimental studies, 1 as well as those of MacLeod, 2 have shown that inadequate treatment of pneumococcal infections with sulfapyridine leads to development of organisms which are resistant or fast to that drug. Whether these sulfapyridine-fast pneumococci are equally fast to other sulfanilamide derivatives, such as sulfathiazole and sulfamethylthiazole, is a matter of theoretical and practical interest. Consequently, we have studied the reactions of 2 of our sulfapyridine-fast strains to these latter drugs.

Essentially identical experiments have been performed with each fast strain and with the parent strains from which these fast organisms were derived.∗ Mice in groups of 100 were infected intraperi-toneally, each mouse receiving 10^-6 cc of a 12 hour blood broth culture. Ten mice from each group were untreated. The remaining 90 were divided into 3 equal groups which were treated with sulfapyri-dine, sulfathiazole or sulfamethylthiazole†-20 mg doses of the respective drug being administered at 2, 8, 14 and 22 hours after infection and at 8 hour intervals thereafter for either 5 additional days (in the experiments with the parent strains) or as long as the mice survived (in the experiments with the fast strains). The drugs were administered as 10% suspensions in 10% acacia.

The results in the accompanying table show conclusively that sulfapyridine-fast pneumococci were also equally resistant to sulfathiazole and sulfamethylthiazole. Thus the mice infected with strain McGovern lived an average of 41 hours under sulfapyridine treatment and 40 and 38 hours under sulfathiazole and sulfamethylthiazole treatments. In the experiment with strain Wistuba, the average survival times were 39, 38 and 39 hours under therapy with the respective drugs.

The table shows also that these drugs were essentially equal in effectiveness against infections with the parent strains.