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295vitamin KI. For comparison, sulfadiazine and sulfathiazole were given once every 24 hours to one group of mice and every 6 hours to another group. The results of these experiments are given in Tables I and 11. For simplicity, only the results at daily intervals with D. pneumonice and S . schottmulleri are given. Essentially the same findings were obtained with Strep. hemolyticus and S . aert ryc ke .When all 3 drugs were given once daily, sulfaquinoxaline was superior to sulfadiazine or sulfathiazole, in that a single daily dose of 40 mg per mouse protected 72.5% of the mice infected with D. pneumonia? Type I. Under the same conditions sulfadiazine and sulfathiazole protected only 27% and 0% respectively. Moreover, single daily doses of sulfaquinoxaline in severe pneumococcal infections compared favorably with multiple daily doses of sulfadiazine or sulfathiazole ( Table I ) . This was found when 20 mg of sulfaquinoxaline was given as a daily dose, as compared with 20 mg of sulfadiazine or sulfathiazole divided into four 6-hourly doses of 5 mg per mouse. Both drugs protected about 50% of the mice.Tests performed to determine the efficacy of sulfaquinoxaline when given at intervals other than every 24 hours, showed that if treatment was given every 36 or 48 hours, a dose of 40 mg/mouse of sulfaquinoxaline was not sufficient to protect mice from severe infection.Blood Levels. The striking therapeutic effects obtained with single daily doses of sulfaquinoxaline may be explained by the fact that this drug remains in the blood for long periods of time and consequently, therapeutic blood concentrations can be maintained by infrequent drug administration. Thus, applying the method of Bratton and Marshall: it was found that a concentration of 3 to 7 mg% was still present in the blood of mice 24 hours after the administration of a single dose of 20 mg per 20 g mouse. Even after 72 hours, small quantities of the drug could be detected in the blood. When the interval between treatments was extended beyond 24 hours, the blood concentration of sulfaquinoxaline fell below the effective range, with the resulting death of the animal.Summary. Sulfaquinoxaline was found to be active against certain bacteria both in vitro and in vivo. Single daily doses of this drug were more effective than single daily doses of sulfadiazine or sulfathiazole. These findings may be explained by the fact that sulfaquinoxaline remains in the blood for long periods of time.

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