Comparative in vitro activities of norfloxacin (MK-0366) and six commonly used antimicrobial agents against 199 urinary isolates showing various degrees of antibiotic resistance.

The in vitro activity of norfloxacin (MK-0366), a new oral antimicrobial agent, was compared to that of ampicillin, tetracycline, cefazolin, nitrofurantoin, nalidixic acid, and trimethoprim against 199 gram-negative urinary isolates. Among these isolates were ampicillin-resistant Escherichia coli and gentamicin-resistant Pseudomonas aeruginosa and Serratia marcescens. Norfloxacin was the most active antimicrobial agent tested against all isolates studied; it was the only agent active against P. aeruginosa and S. marcescens.