Efficacy of besifloxacin in an early treatment model of methicillin-resistant Staphylococcus aureus keratitis

Purpose: To determine the effectiveness of topically applied besifloxacin, gatifloxacin, and moxifloxacin for the early treatment of experimental methicillin-resistant Staphylococcus aureus (MRSA) keratitis.

Methods: Ten hours post-MRSA Infection, rabbit eyes were treated topically with 19 doses of phosphate-buffered saline (PBS), besifloxacin, gatifloxacin, or moxifloxacin. Slit-lamp examinations were performed before and after the inoculation. Corneas were harvested for Bacterial quantitation and minimal inhibitory concentrations (MICs) were determined.

Results: All 3 fluoroquinolones significantly lowered the clinical severity of the Infection as compared to treatment with PBS (P < 0.05). However, the mean log(10) colony-forming unit (CFU) recovered from besifloxacin-treated corneas was significantly lower than all Other treatment groups (P < 0.01). CFU recovered from corneas treated with moxifloxacin and PBS showed no significant difference (P = 0.12). Corneas treated with gatifloxacin had a significantly lower log(10) CFU recovered as compared to PBS-treated corneas (P < 0.01). The MICs for gatifloxacin and moxifloxacin were 8 microg/mL, whereas the MIC for besifloxacin was 1 microg/mL.

Conclusions: All 3 fluoroquinolones significantly lowered the clinical severity of the Infection. Besifloxacin had an 8-fold lower MIC for MRSA than gatifloxacin and moxifloxacin, and was significantly more effective than gatifloxacin and moxifloxacin in reducing the number of MRSA in the rabbit cornea.