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M. E. Marquart, M. E. Sanders, E. W. Norcross, Q. C. Moore, III, A. Shafiee; Efficacy of Besifloxacin in the Treatment of Methicillin-Resistant Staphylococcus aureus Keratitis. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2669.
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To determine the effectiveness of topically applied besifloxacin (0.6%), gatifloxacin (0.3%), and moxifloxacin (0.5%) for the treatment of experimental methicillin-resistant Staphylococcus aureus (MRSA) keratitis.
One hundred colony-forming units (CFU) of MRSA (blood isolate, G.V. Sonny Montgomery V.A. Medical Center, Jackson, MS) were injected intrastromally into rabbit corneas. Ten hours after infection, one topical drop of PBS, besifloxacin, gatifloxacin, or moxifloxacin was applied to each eye every 15 minutes for 5 doses and then every 30 minutes for 14 doses. Eyes were examined before and after treatment by slit lamp biomicroscopy. Corneas were harvested from treated and untreated rabbits for the quantitation of bacteria. Minimal inhibitory concentrations (MICs) were determined in vitro for each fluoroquinolone.
The baseline log10 CFU recovered from corneas prior to treatment was 6.713 ± 0.093. Besifloxacin was most effective at reducing the bacterial CFU following treatment (P < 0.001 compared to the PBS group; n = 12 corneas per group). The average log10 CFU of MRSA recovered from besifloxacin-treated corneas (3.569 ± 0.378) was significantly lower than the CFU recovered from corneas treated with gatifloxacin (5.652 ± 0.396), and moxifloxacin (6.243 ± 0.387; P < 0.001). The average log10 CFU recovered from the PBS-treated corneas at 19 hours post-infection was 7.392 ± 0.095. All three of the fluoroquinolone treatments decreased the clinical severity compared to the control group (P < 0.010; n = 16 corneas per group). The clinical scores from the three treatment groups were not significantly different from each other (P > 0.050). The MICs for gatifloxacin and moxifloxacin against the MRSA strain were each 8 µg/ml, and the MIC for besifloxacin was 1 µg/ml.
These data suggest that besifloxacin is more effective than gatifloxacin and moxifloxacin in reducing the number of MRSA in the cornea when applied topically from 10 to 18 hours post-infection.
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