In vitro activity of pefloxacin compared to that of quinolones and other antimicrobial agents.

Pefloxacin is a new methyl-4-piperazinyl quinolone. It had MIC90 values of less than 0.01 to 0.8 micrograms/ml for the majority of Escherichia coli, Klebsiella, oxytoca, Citrobacter, Providencia, Enterobacter cloacae, Enterobacter aerogenes, Morganella and Proteus mirabilis. It inhibited ampicillin, cephalexin and nalidixic acid resistant isolates of these species. Against Pseudomonas the pefloxacin MIC90 was 3.1 micrograms/ml. Staphylococcus aureus had a MIC50 of 0.4 micrograms/ml and a MIC90 of 0.8 micrograms/ml and S. faecalis had a MIC90 of 3.1 micrograms/ml. Pefloxacin inhibited Salmonella spp., Salmonella typhi, Shigella spp., Yersinia, Aeromonas, toxigenic E. coli at concentrations of less than 0.05 to 1.6 micrograms/ml, including ampicillin and trimethoprim resistant strains. There was a minimal difference in MIC and MBC values in broth or serum, but major changes in MIC and MBC values occurred in acid urine. Increase in MIC values occurred with repeated transfer in broth or urine.