A-61827 (A-60969), a new fluoronaphthyridine with activity against both aerobic and anaerobic bacteria.

A-61827 (A-60969 is the hydrochloric salt of A-61827) is a new aryl-fluoronaphthyridine which is active against aerobic and anaerobic bacteria. The MICs of A-61827 for 90% of strains (MIC90) of staphylococci and streptococci were less than or equal to 1 microgram/ml and were generally 1 to 4 twofold dilutions less than those of ciprofloxacin for these bacteria. The MIC90S of A-61827 for members of the family Enterobacteriaceae and Pseudomonas aeruginosa were also less than or equal to 1 microgram/ml. Ciprofloxacin was 1 to 3 twofold dilutions more active than A-61827 against these gram-negative bacteria. Neisseria gonorrhoeae, Campylobacter jejuni, and Haemophilus influenzae were susceptible to less than 0.06 microgram of A-61827 per ml. The MIC90 of A-61827 for Legionella pneumophila was 0.25 microgram/ml. A-61827 was as potent or 1 to 2 twofold dilutions more potent than ciprofloxacin against these organisms. The MIC90 of A-61827 for all anaerobic bacteria was less than or equal to 4 micrograms/ml compared with less than or equal to 32 micrograms/ml for ciprofloxacin. In mouse protection tests, A-61827 was as active as ciprofloxacin against Escherichia coli, P. aeruginosa, and Salmonella typhimurium and 5 to 10 times more active than ciprofloxacin against Staphylococcus aureus and Streptococcus pyogenes. A-61827 was as active as ciprofloxacin against P. aeruginosa in a mouse pyelonephritis model and more active than ciprofloxacin and metronidazole in a mouse Bacteroides fragilis abscess model. After oral administration of 100 mg/kg to mice, the peak concentrations of A-61827 and ciprofloxacin in serum were 2.3 and 2.4 micrograms/ml and the half-lives in serum were 3.9 and 1.2 h, respectively.