title: Comparison of ciprofloxacin and ofloxacin using human corneal susceptibility levels.
abstract: OBJECTIVE
  We compared the in vitro susceptibility of gram-positive bacteria to ciprofloxacin and ofloxacin using human corneal susceptibility levels.
  
  
  METHODS
  The concentrations of ciprofloxacin and ofloxacin that can be attained in 99% of human corneas (Cornea99) after topical administration were calculated statistically from reported data. The minimal inhibitory concentrations (MICs) were determined for 95 corneal isolates of gram-positive bacteria (51 Staphylococcus aureus, 16 Streptococcus pneumoniae, 16 Streptococcus viridans group, and 12 coagulase-negative staphylococci). Susceptibility was interpreted by comparing the MICs with the respective Cornea99 for each antibiotic. Time-kill studies of representative gram-positive bacteria were tested using the Cornea99 and the maximal corneal concentrations reported for ciprofloxacin and ofloxacin.
  
  
  RESULTS
  The Cornea99 of ciprofloxacin and ofloxacin were calculated to be 3.57 microg/ml (n = 22) and 2.22 microg/ml (n = 20), respectively. The reported mean corneal concentrations of ciprofloxacin (6.90 +/- 6.20 microg/ml) and ofloxacin (5.71 +/- 6.15 microg/ml) were comparable (p = 0.54). All gram-positive bacteria were equally susceptible to ciprofloxacin and ofloxacin (p = 0.54) based on the Cornea99. The time-kill studies determined that 8-24 h were required for both ciprofloxacin and ofloxacin to reach bactericidal levels.
  
  
  CONCLUSIONS
  Ciprofloxacin and ofloxacin demonstrated comparable penetration into the cornea and provided equivalent in vitro efficacy against representative gram-positive bacteria. Time-kill studies indicated that 8-24 h of continual corneal concentrations of ciprofloxacin and ofloxacin were necessary in this study to reduce susceptible gram-positive bacteria by 99.9%.
authors.affiliation: The University of Pittsburgh and Medical Center, Pennsylvania 15213, USA.
authors.forename: R P
authors.initials: RP
authors.lastname: Kowalski
authors.forename: L M
authors.initials: LM
authors.lastname: Karenchak
authors.forename: Y J
authors.initials: YJ
authors.lastname: Gordon
mesh_terms: D000890:Anti-Infective Agents / Q000493:pharmacokinetics / Q000494:pharmacology*; D001682:Biological Availability; D002939:Ciprofloxacin / Q000493:pharmacokinetics / Q000494:pharmacology*; D015169:Colony Count, Microbial; D003315:Cornea / Q000378:metabolism* / Q000382:microbiology; D006094:Gram-Positive Bacteria / Q000187:drug effects* / Q000254:growth & development / Q000302:isolation & purification; D006801:Humans; D007634:Keratitis / Q000378:metabolism / Q000382:microbiology; D008826:Microbial Sensitivity Tests; D015242:Ofloxacin / Q000493:pharmacokinetics / Q000494:pharmacology*; D012189:Retrospective Studies
chemical_list: D000890:Anti-Infective Agents; D002939:Ciprofloxacin; D015242:Ofloxacin