To assess the potential of fluoroquinolones as topical antimicrobial agents, we evaluated in vitro the antimicrobial activity of five fluoroquinolones (ciprofloxacin, norfloxacin, ofloxacin, pefloxacin, and temafloxacin), as well as gentamicin, tobramycin, and cefazolin against 96 isolates of common bacterial corneal pathogens. Ciprofloxacin and temafloxacin were the most active quinolones [minimal inhibitory concentration inhibiting 90% of stains (MIC90) of 1 microgram/ml], followed by ofloxacin (MIC90 2 micrograms/ml), and norfloxacin and pefloxacin (MIC90s 4 micrograms/ml). In contrast, gentamicin and tobramycin MIC90s were 32 and 64 micrograms/ml, respectively; cefazolin MIC90 was greater than 2048 micrograms/ml. The corneal epithelial cytotoxicity of the fluoroquinolones also was evaluated utilizing an in vitro assay of 3H-thymidine uptake of rabbit corneal epithelial cell cultures. The least to greatest toxicity of the fluoroquinolones were as follows: ciprofloxacin and temafloxacin less than norfloxacin less than ofloxacin less than pefloxacin. Our study suggests that the fluoroquinolones, especially ciprofloxacin and temafloxacin, possess excellent in vitro activity against common bacterial corneal pathogens and are less toxic to the corneal epithelium than the aminoglycosides.

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We assessed in vitro the antimicrobial activity of four agents (vancomycin, teicoplanin, mupirocin, and imipenem) which are effective against Gram-positive cocci causally associated with bacterial keratitis, as well as their corneal epithelial cytotoxicity. Minimal inhibitory concentrations inhibiting 90% of strains (MIC90s) against 10 strains each of methicillin-susceptible and -resistant Staphylococcus aureus and Staphylococcus epidermidis, penicillin-susceptible and -resistant Streptococcus pneumoniae, and viridans group streptococci were as follows: vancomycin (MIC90s 0.25-2 micrograms/ml), teicoplanin (MIC90s 0.25-4 micrograms/ml, mupirocin (MIC90s 0.12-4 micrograms/ml), and imipenem (MIC90s 0.008-0.25 micrograms/ml, except for methicillin-resistant staphylococci with MIC90 of 16 micrograms/ml). Cytotoxicity was assayed by uptake of 3H-thymidine by rabbit corneal epithelial cell cultures at drug concentrations of 12.5-100 mg/ml for vancomycin and teicoplanin, 1-8 mg/ml for mupirocin and 0.125-8 mg/ml for imipenem, with exposure times of 5, 30 and 60 min. Cytotoxicity was as follows: imipenem < mupirocin < vancomycin < or = teicoplanin. Resistance to methicillin-resistant S. aureus and S. epidermidis for imipenem and resistance to S. epidermidis and cytotoxicity for teicoplanin limit their consideration for suspected Gram-positive keratitis. On the other hand, vancomycin and mupirocin, because of their excellent therapeutic indices, should be considered for this indication.