Pefloxacin: evolution of in vitro activity during 18 months of use in an intensive care unit

The MIC of pefloxacin against all the strains (3122) isolated in an intensive care unit during 18 months was studied. The MIC of pefloxacin was estimated by standard agar diffusion method in Mueller-Hinton agar. All the strains with a MIC lower than 2 mg/l were considered as sensitive, between 2 and 4 mg/l as "intermediary" and over 4 mg/l as resistant. Geometrical means of MICs were calculated for each month and for different species. The study continued for 18 months from the introduction of the drug which was in widespread and constant use as a first-choice antibiotic. No significant increase was detected in the incidence of resistant strains during the study; on the other hand, small, limited clusters of resistant strains were observed during minor nosocomial epidemics. The general features of quinolone activity, the spectrum of this new quinolone and the slow evolution of the bacterial population are discussed.