2009 OMIG, Abstract 15

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The Evaluation of Levofloxacin 1.5% in the Treatment of Levofloxacin-Susceptible and Resistant  Staphylococcus aureus and Pseudomonas aeruginosa in Rabbit Keratitis Models.
E.G. Romanowski, R.P. Kowalski, F.S. Mah, R.M.Q. Shanks, Y.J. Gordon
The Charles T. Campbell Ophthalmic Microbiology Laboratory, UPMC Eye Center, Ophthalmology and Visual Sciences Research Center, Eye and Ear Institute, Department of Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, PA.
                                                                    
Purpose: We evaluated topical levofloxacin (LEV) 1.5% for reducing LEV-susceptible and resistant (serum standard interpretation) Staphylococcus aureus (SA) and Pseudomonas aeruginosa (PA) in rabbit keratitis models.
Methods: For LEV-susceptible and resistant SA, respectively, 32 NZW rabbits were intrastromally injected with 1000 colony forming units (CFU). After 4 hours, the corneas of 8 rabbits were homogenized to determine onset of therapy CFU/ml. The 24 remaining rabbits were equally divided into 3 treatment groups: LEV 1.5%, fortified cefazolin (CEF) 5% (LEV-susceptible SA) or fortified vancomycin (VAN) 5% (LEV-resistant SA), and saline. 21 drops were administered over 5 hours. One hour post-treatment, the corneas were homogenized for CFU/ml. For LEV-susceptible and resistant PA, respectively, 32 NZW rabbits were intrastromally injected with 1000 CFU. After 16 hours, the corneas of 8 rabbits were homogenized for CFU/ml at the onset of therapy. The 24 remaining rabbits were equally divided into 3 treatment groups: LEV 1.5%, ciprofloxacin (CIP) 0.3% or fortified tobramycin (TOB) 1.4% (LEV-resistant PA), and saline. 19 drops were administered over 8 hours. One hour post-treatment, the corneas were homogenized for CFU/ml. The CFU/ml data were analyzed for sterilization and non-parametrically for reduction.
Results: LEV 1.5% and all comparator antibiotics significantly reduced corneal colony counts compared to the saline and onset controls for all bacterial categories (P<0.05). Among the antibiotic groups, LEV 1.5% significantly was more effective than fortified VAN 5% (p<0.05) for LEV-resistant SA, and was equivalent to the other comparator antibiotics for the other bacterial categories in reducing corneal colony counts. LEV 1.5% sterilized all corneas in the LEV-susceptible (16/16) and resistant (16/16) PA groups which were similar to the comparators (CIP 16/16 and TOB 13/16). LEV 1.5% (16/16) sterilized more corneas than CEF 5% (8/16) for LEV-susceptible SA (P=0.0024). Neither LEV 1.5% (0/16) nor VAN 5% (1/16) was effective in sterilizing LEV-resistant SA. No corneas were sterilized by saline.
Conclusion: Topical LEV 1.5% was effective in reducing SA and PA corneal colony counts in the rabbit keratitis modelsregardless of in vitro susceptibility.
Disclosure code: F, C        
Support: Vistakon Pharmaceuticals LLC, NIH Core Grant EY08098 (OVSRC), Eye & Ear Foundation of Pittsburgh, RPB.