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The ideal ophthalmic anti-infective exhibits broad-spectrum activity against gram-positive, 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. Gatifloxacin and moxifloxacin exhibited similar activity against 6 gram-positive organisms: Staphylococcus epidermidis, Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus pyogenes, Bacillus cereus, and Enterococcus 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 against Streptococcus 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 against Pseudomonas aeruginosa was 1.28 mg/mL compared with 2.60 mg/ mL for moxifloxacin (P = .023). MIC90 values for gatifloxacin against Klebsiella pneumoniae and Enterobacter aerogenes were one fourth to one fifth the values for moxifloxacin. For the atypicals, the MIC90 values for gatifloxacin against Nocardia asteroides and Mycobacterium chelonae were one fourth the corresponding values for moxifloxacin. 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. [ABSTRACT FROM AUTHOR]