Gatifloxacin and moxifloxacin: An in vitro susceptibility comparison to levofloxacin, ciprofloxacin, and ofloxacin using bacterial keratitis isolates

.PURPOSE: We compared the in vitro susceptibility patterns and the minimum inhibitory concentrations (MICs) of gatifloxacin (GAT) and moxifloxacin (MOX) (fourth-generation fluoroquinolones) to ciprofloxacin (CIP) and ofloxacin (OFX) (second-generation fluoroquinolones) and levofloxacin (LEV; third-generation flu-oroquinolone) using bacterial keratitis isolates. The goal was to determine whether the fourth-generation fluoro. quinolones offer any advantages over the second- and third-generation fluoroquinolones. .DESIGN: Experimental laboratory investigation. In contrast to an epidemiologic prevalence study, this study was designed to compare the relative susceptibility of each bacterial group to different fluoroquinolones by deliberate selection of representative isolates that were both susceptible and resistant to second-generation fluoro, quinolones. .METHODS: In retrospect, the MICs of 177 bacterial keratitis isolates were determined to CIP, OFX, LEV, GAT, and MOX using E tests. A relative susceptibility analysis was performed for each bacterial group that included separate bacterial groups that were resistant second-generation fluoroquinolones. The NCCLS sus, ceptibility patterns and the MICs were compared statis. tically. Comparing MICs, the antibiotic with the lower MICs has greater antibacterial activity. . RESULTS: For most keratitis isolates, there were no susceptibility differences among the five fluoroquinolones. The fourth-generation fluoroquinolones did, however, demonstrate increased susceptibility for Staph ylococcus aureus isolates that were resistant to CIP, LEV and OFX. In general, CIP demonstrated the lowest MICs for gram-negative bacteria. The MICs for fourth-generation fluoroquinolones were statistically lower than the second generation fluoroquinolones for all gram-positive bacteria tested. Comparing the two fourth-generation fluoroquinolones, MOX demonstrated lower MICs for most gram-positive bacteria, whereas GAT demonstrated lower MICs for most gram-negative bacteria. . CONCLUSIONS: Based on in vitro testing, the four & generation fluoroquinolones may offer some advantages over those currently available for the treatment of bacterial keratitis. Clinical studies will be required to con. firm these results. (C) 2003 by Elsevier Inc. All rights reserved.