Antibacterial activity of the fourth-generation fluoroquinolones gatifloxacin and moxifloxacin against ocular pathogens

Abstract

The ideal ophthalmic anti-infective exhibits broad-spectrum activity against grampositive, gram-negative, and atypical bacterial species. These pathogens can cause potentially blinding infections such as keratitis and endophthalmitis, both of which are associated with ophthalmic surgery or traumatic injury. These infections often require aggressive antibacterial therapy, preferably with newer generations of antibiotics. In this study, minimal inhibitory concentration (MIC) values for gatifloxacin and moxifloxacin were determined in vitro against bacterial strains that were isolated from suspected cases of bacterial keratitis and endophthalmitis. The ocular isolates included 7 gram-positive, 4 gram-negative, and 3 atypical bacterial species. Catifloxacin and moxifloxacin exhibited similar activity against 6 grampositive organisms:Staphylococcus epidermidis, Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus pyogenes, Bacillus cereus, andEnterococcus faecalis. MIC₉₀ values for the drugs against these isolates ranged from 0.08 mg/mL to 0.57 mg/mL and were comparable to previously published values against isolates from patients with systemic infections. The MIC₉₀ for gatifloxacin againstStreptococcus viridans was 0.22 mg/mL compared with 0.73 mg/mL for moxifloxacin (P=.011). Among the gram-negative isolates, the mean MIC₉₀ for gatifloxacin againstPseudomonas aeruginosa was 1.28 mg/mL compared with 2.60 mg/ mL for moxifloxacin (P=.023). MIC₉₀ values for gatifloxacin againstKlebsiella pneumoniae andEnterobacter aerogenes were one fourth to one fifth the values for rnoxifloxacin. For the atypicals, the MIC₉₀ values for gatifloxacin againstNocardia asteroides andMycobacterium chelonae were one fourth the corresponding values for rnoxifloxacin. Gatifloxacin demonstrated a broad spectrum of activity against several key ocular pathogens tested in this study and was at least as effective as moxifloxacin against these pathogens.