In vitro activity of pefloxacin

A broth dilution method was used to measure the minimal inhibitory concentrations of pefloxacin, a new quinolone derivative. Because this new agent could be used in systemic infections, mezlocillin, cefotaxime, ceftazidime and amikacin were used as comparative agents. Pefloxacin was found to be more active than mezlocillin and as active as or more active than cefotaxime, ceftazidime and amikacin. With the exception of Serratia marcescens, only 7% of Enterobacteriaceae strains were resistant to pefloxacin with a MIC greater than 8 micrograms/ml. Pefloxacin was also found to be the best agent against the non-fermenters Staphylococcus aureus and St. epidermidis. Resistance to ampicillin, carbenicillin and gentamicin did not affect the effectiveness of pefloxacin. However, pefloxacin appeared more susceptible to nalidixic acid resistance, with MICs four to sixfold higher.