Effectiveness of ciprofloxacin, levofloxacin, or moxifloxacin for treatment of experimental Staphylococcus aureus keratitis

Abstract

The purpose of this study was to quantitatively compare, in a rabbit keratitis model, the levels of effectiveness of moxifloxacin, levofloxacin, and ciprofloxacin for the treatment of Staphylococcus aureus isolates of diverse antibiotic susceptibilities. Rabbit eyes were intrastromally injected with approximately 100 CFU of methicillin-sensitive or methicillin-resistant S. aureus (MSSA or MRSA, respectively) organisms that were either sensitive or resistant to ofloxacin. One drop of moxifloxacin (0.5%), levofloxacin (0.5%), or ciprofloxacin (0.3%) was topically applied hourly from 4 to 9 (early) or 10 to 15 (late) h postinfection. At 1 h after cessation of therapy, the corneas were harvested, and the number of CFU per cornea was determined. For the ofloxacin-sensitive strains, early treatment of MSSA or MRSA with moxifloxacin, levofloxacin, or ciprofloxacin produced approximately a 5-log decrease in CFU per cornea relative to that in untreated eyes (P </= 0.0001). For late therapy of ofloxacin-sensitive strains, moxifloxacin, levofloxacin, and ciprofloxacin produced approximately 5-, 4-, and 2- to 3-log reductions in CFU per cornea, respectively (P </= 0.0001). Early treatment of the ofloxacin-resistant strains with either moxifloxacin or levofloxacin produced a >/=4-log or >/=3-log decrease, respectively, in the MSSA or MRSA strains (P </= 0.0001), whereas ciprofloxacin treatment produced a 1-log decrease in CFU per cornea relative to that in untreated eyes (P = 0.1540). For late treatment of ofloxacin-resistant strains, levofloxacin and ciprofloxacin failed to significantly reduce the number of CFU per cornea (P >/= 0.3627), whereas moxifloxacin produced a significant reduction in CFU per cornea of approximately 1 log (P </= 0.0194). Therefore, for three of the four treatments tested, moxifloxacin demonstrated greater effectiveness than either levofloxacin or ciprofloxacin.

FIG. 1.

Fluoroquinolone treatment of rabbit eyes infected with ofloxacin-sensitive S. aureus strains. Rabbit corneas were infected with ofloxacin-sensitive S. aureus and treated with moxifloxacin (0.5%), levofloxacin (0.5%), or ciprofloxacin (0.3%). Rabbit eyes were treated every hour from 4 to 9 (A and B) or from 10 to 15 (C and D) h p.i. Following sacrifice of the rabbits, the numbers of viable S. aureus organisms per cornea was quantified and expressed as base 10 logarithms ± standard deviations (indicated by error bars). The number of eyes per group (n) was 6 unless specified by one of the following labels above the error bars: (a), n = 12; (b), n = 15; (c), n = 22; (d), n = 10; (e), n = 18.

FIG. 2.

Fluoroquinolone treatment of rabbit eyes infected with ofloxacin-resistant S. aureus strains. Rabbit corneas were infected with ofloxacin-resistant S. aureus and treated with moxifloxacin (0.5%), levofloxacin (0.5%), or ciprofloxacin (0.3%). Rabbit eyes were treated every hour from 4 to 9 (A and B) or from 10 to 15 (C and D) h p.i. Following sacrifice of the rabbits, the numbers of viable S. aureus organisms per cornea were quantified and expressed as base 10 logarithms ± standard deviations (indicated by error bars). The number of eyes per group (n) was 6 unless specified by one of the following labels above the error bar: (a), n = 17; (b), n = 13; (c), n = 12; (d), n = 26; (e), n = 20.