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2002 Ocular Microbiology and Immunology Group, Abstract 3

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Susceptibility of Ocular Isolates to Gatifloxacin and Older Fluoroquinolones
Monica Monica, MD1; Harold Jensen, PhD2; The Allergan Gatifloxacin Study Group2
1Private Practice, New Orleans, LA; 2Allergan

Purpose: To determine susceptibility of ocular isolates to the 4th generation
fluoroquinolone, gatifloxacin, and to the 3rd generation fluoroquinolones, levofloxacin and ciprofloxacin.

Methods: Conjunctival swabs were taken from patients with bacterial conjunctivitis in a clinical trial of gatifloxacin, prior to any antibacterial therapy. MICs for individual isolates from the swabs were classified using NCCLS susceptibility breakpoints.

Results: All Gram-positive ocular isolates (n=170) were susceptible to gatifloxacin, except for a single strain of Staphylococcus haemolyticus which displayed intermediate resistance. In contrast, 1.8% and 8.8% of Gram-positives were resistant in an intermediate range, and 2.9% and 7.6% were fully resistant, to levofloxacin and ciprofloxacin, respectively. All isolates of Staphylococcus epidermidis (n=38), a species frequently encountered in ocular infections, were susceptible to gatifloxacin. However, 10.5% and 15.8% of S. epidermidis ocular isolates were resistant to levofloxacin and ciprofloxacin respectively, and another 5.3% showed intermediate resistance to levofloxacin. The MIC90 for S. epidermidis ocular isolates was 2.0 µg/ml for gatifloxacin compared to 8.0 and 32.0 µg/ml for levofloxacin and ciprofloxacin, respectively. For Streptococcus pneumoniae (n=30), the MIC90 was 0.25 µg/ml for gatifloxacin, compared to 1.0 µg/ml for levofloxacin and ciprofloxacin. All of the Gram-negative isolates (n=65) were susceptible to all 3 antibacterials.

Conclusions: Substantial percentages of Gram-positive species isolated from bacterial conjunctivitis patients were resistant or partially resistant to levofloxacin and ciprofloxacin, however, the same strains were susceptible to the 4th generation fluoroquinolone, gatifloxacin. Compared to older fluoroquinolones, gatifloxacin displays clearly improved activity against Gram-positive ocular isolates in vitro.

This research was supported by funding from Allergan Inc.

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