2009 OMIG, Abstract 14

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Prophylactic Treatment of Staphylococcus aureus Infection in the Rabbit Anterior Chamber with Vigamox or Besivance.
C.L. Balzli, A. Caballer, A. Tang, C.C. McCormick, R. J. O’Callaghan
Department of Microbiology, University of Mississippi Medical Center, Jackson, MS

Purpose: By utilizing a rabbit model of Staphylococcus aureus endophthalmitis, this study compared the therapeutic penetration of two commercial ocular fluoroquinolones.
Methods: The minimum inhibitory concentrations (MIC) of moxifloxacin (0.5%, Vigamox) and besifloxacin (0.6%, Besivance) on S. aureus strain UMCR1 were determined. Rabbit eyes (n ≥ 10 per group) were topically treated with a single drop (45 µl) of moxifloxacin or besifloxacin at 30 minutes or 60 minutes prior to infection. Rabbit eyes were rinsed with phosphate buffered saline immediately before injection of 106 colony forming units (CFU) of log phase UMCR1 in 10 µl of tryptic soy broth into the anterior chamber. The aqueous humor was removed 30 minutes following infection and viable bacteria were quantified as log CFU/ml.
Results: The MIC of moxifloxacin was determined to be 0.06 µg/ml, and 0.03 µg/ml of besifloxacin for strain UMCR1. Rabbit eyes that were treated 30 minutes prior to infection with besifloxacin yielded 4.79 ± 0.31 logs CFU/ml of aqueous humor, which was not significantly different (P = 0.2080) from untreated controls (5.22 ± 0.11 logs CFU/ml). The eyes treated with moxifloxacin 30 minutes prior to infection produced 2.17 ± 0.26 logs CFU/ml of aqueous, a number significantly lower than untreated controls and besifloxacin treated eyes (P < 0.0001 and P < 0.0001, respectively). Eyes treated 60 minutes prior to infection with besifloxacin had 4.83 ± 0.19 logs CFU/ml of aqueous, which was not significantly less (P = 0.3942) than untreated controls (5.04 ± 0.16 logs CFU/ml). However, eyes treated with moxifloxacin 60 minutes prior to infection had significantly less bacteria (3.43 ± 0.34 logs CFU/ml) than untreated control and besifloxacin treated eyes (P = 0.0005 and 0.0020, respectively).
Conclusion: This study was a quantitative determination of the prophylactic effectiveness of topical moxifloxacin and besifloxacin within the anterior chamber of the eye. While the MIC was slightly lower for besifloxacin, moxifloxacin demonstrated significantly greater bacterial killing as compared to besifloxacin when applied either 30 or 60 minutes before infection in this model of endophthalmitis.
Disclosure = F