In vitro Efficacy of Alternatives to Moxifloxacin and Gatifloxacin for Coagulase–Negative Staphylococcus (CNS)

Abstract

Abstract: : Purpose: Coagulase negative staphylococcus is the most common isolate in postoperative endophthalmitis. Fluoroquinolone antibiotics, especially moxifloxacin and gatifloxacin, are commonly used as prophylaxis against perioperative infection. As fluoroquinolone resistance is a growing concern, the purpose of this study is to compare the in vitro efficacy of gemifloxacin, linezolid, vancomycin, and quinupristin/dalfopristin to existing fluoroquinolones against human coagulase–negative staphylococcal (CNS) endophthalmitis isolates. Methods: Sample organisms from 35 CNS endophthalmitis isolates recovered between 1993 and 2004 were removed from the freezer and reconstituted. E–tests and disc diffusion methods were used to compare susceptibility patterns against gemifloxacin, moxifloxacin, gatifloxacin, linezolid, quinupristin/dalfopristin, and vancomycin. Inhibitory quotients (C_max / MIC₉₀) were calculated using published C_max values. C_max in this study is defined as the maximum attainable aqueous concentration using topical therapy. MIC₉₀ is defined as the minimum concentration of antibiotic necessary to inhibit 90% of isolates. Results: The percent of CNS isolates susceptible are (in descending order): vancomycin (100%), linezolid (100%), quinupristin/dalfopristin (100%), gemifloxacin (88.6%), moxifloxacin (76.5%), and gatifloxacin (74.2%). The MIC₉₀ values are (in decreasing order of efficacy): quinupristin/dalfopristin (0.75 µg/ml), vancomycin (3 µg/ml), linezolid (4 µg/ml), gemifloxacin (> 32 µg/ml), moxifloxacin (> 32 µg/ml), and gatifloxacin (> 32 µg/ml). Inhibitory quotients are: vancomycin (1.3), gatifloxacin (0.06), and moxifloxacin (0.008). Aqueous Cmax values for the other antibiotics in this study are unavailable. Conclusions: In the current study, vancomycin, linezolid, and quinupristin/dalfopristin were the most effective antibiotics against CNS. Moxifloxacin, gatifloxacin, and gemifloxacin were less effective and individually inhibited less than 90% of the isolates at concentrations measurable by the available E–tests. This suggests that fluoroquinolones may not offer ideal prophylaxis against coagulase–negative staphylococcus.

Keywords: endophthalmitis • antibiotics/antifungals/antiparasitics • Staphylococcus