In vitro antibacterial activity of norfloxacin (MK-0366).

The in vitro activity of norfloxacin (MK-0366) compared with that of beta-lactam antibiotics and, where appropriate of gentamicin or metronidazole was assessed against recent clinical isolates of common bacteria. The compound was highly active against most enterobacteria (minimal inhibitory concentrations [MICs], 0.008 to 32 micrograms/ml; 90% inhibited by 0.25 micrograms/ml), Haemophilus influenzae (MICs, 0.03 to 0.12 micrograms/ml), and Neisseria gonorrhoeae (MICs, 0.008 to 0.016 micrograms/ml). It was also active against Pseudomonas aeruginosa (MICs, 0.12 to 2 micrograms/ml), most other pseudomonads (MICs, 0.03 to 32 micrograms/ml), and Acinetobacter calcoaceticus (MICs 0.06 to 4 micrograms/ml). Norfloxacin was somewhat less active against staphylococci (MICs, 0.25 to 4 micrograms/ml; 1 microgram/ml required to inhibit 50% of isolates) and streptococci (MICs, 0.5 to 64 micrograms/ml). Members of the Bacteroides fragilis group of anaerobes were relatively resistant to norfloxacin (MICs, 8 to 128 micrograms/ml), as were most other anaerobes.