title: The in vitro impact of moxifloxacin and gatifloxacin concentration (0.5% vs 0.3%) and the addition of benzalkonium chloride on antibacterial efficacy.
abstract: OBJECTIVE
  Varied concentrations of moxifloxacin (MOX) and gatifloxacin (GAT) and the addition of 0.005% benzalkonium chloride (BAK) were evaluated for eliminating Staphylococcus aureus (SA), Pseudomonas aeruginosa (PA), and coagulase-negative Staphylococcus (CNS).
  
  
  METHODS
  In vitro laboratory investigation.
  
  
  METHODS
  The time-kill survival of SA, PA, and CNS were tested at one, two, three, six, eight, and 24 hours to: (1) Mueller-Hinton broth, (2) BAK, (3) 0.5% MOX, (4) 0.5% GAT, (5) 0.3% MOX, (6) 0.3% GAT, (7) 0.3% GAT plus BAK, (8) 0.5% MOX plus BAK, (9) 8 microg/ml GAT, and (10) 8 mug/ml MOX. Antibiotic interactions (GAT and BAK) were determined by checkerboard testing. The outcome measures were (1) time-to-kill, (2) killing-rates, and (3) fractional inhibitory concentration (FIC) indices.
  
  
  RESULTS
  MOX and GAT at either 0.5% or 0.3% had equivalent antibacterial effects. BAK alone or the addition of BAK to either antibiotic eliminated SA and CNS within one hour, whereas 0.3% GAT plus BAK eliminated bacteria faster than 0.5% MOX (P = .016). For PA, BAK alone had no antibacterial effect. The kill rates of MOX and GAT were equivalent. FIC indices indicated that GAT and BAK were indifferent against SA and CNS, but antagonistic to PA.
  
  
  CONCLUSIONS
  As a preservative, MOX and GAT have equivalent antibacterial activity with similar killing rates. BAK appears to independently complement GAT for eliminating SA and CNS, but has no effect on PA. The in vitro predictive clinical effect due to varied antibiotic concentration and the addition of BAK requires confirmatory clinical studies for validation.
authors.affiliation: Charles T. Campbell Ophthalmic Microbiology Laboratory at the University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania, USA. kowalskirp@upmc.edu
authors.forename: Regis P
authors.initials: RP
authors.lastname: Kowalski
authors.forename: Brittany R
authors.initials: BR
authors.lastname: Kowalski
authors.forename: Eric G
authors.initials: EG
authors.lastname: Romanowski
authors.forename: Francis S
authors.initials: FS
authors.lastname: Mah
authors.forename: Paul P
authors.initials: PP
authors.lastname: Thompson
authors.forename: Y Jerold
authors.initials: YJ
authors.lastname: Gordon
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology*; D001372:Aza Compounds / Q000494:pharmacology*; D001548:Benzalkonium Compounds / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D024841:Fluoroquinolones / Q000494:pharmacology*; D000077734:Gatifloxacin; D008826:Microbial Sensitivity Tests; D000077266:Moxifloxacin; D011550:Pseudomonas aeruginosa / Q000187:drug effects* / Q000254:growth & development; D011804:Quinolines / Q000494:pharmacology*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000254:growth & development; D013997:Time Factors
chemical_list: D000890:Anti-Infective Agents; D001372:Aza Compounds; D001548:Benzalkonium Compounds; D024841:Fluoroquinolones; D011804:Quinolines; D000077734:Gatifloxacin; D000077266:Moxifloxacin