Benzalkonium chloride enhances the antibacterial efficacy of gatifloxacin in an experimental rabbit model of intrastromal keratitis

Purpose: The aim of this study was to determine whether a preservative (0.005% benzalkonium chloride [BAK]) enhances the antibacterial efficacy of an antibiotic (0.3% gatifloxacin, [GAT]) in vivo. Methods: Rabbits were inoculated intrastromally with GAT-resistant, methicillin-resistant Staphylococcus aureus or Staphylococcus epidermidis and then divided into four treatment groups: 0.3% GAT + 0.005% BAK; 0.3% GAT without BAK; vehicle including 0.005% BAK; and saline control. At 4 h postinoculation, topical treatment was initiated in both eyes every 15 min for 5 h. One (1) h after therapy, corneal colony counts were determined. Results: For S. aureus, duplicate experiments demonstrated that GAT+BAK and GAT without BAK significantly reduced colony counts, compared with BAK or saline (P < 0.05). Further, GAT+BAK significantly reduce Colony Counts, compared with GAT Without BAK. BAK alone was equivalent to the saline control. For S. epidermidis, duplicate experiments demonstrated that GAT+BAK and GAT without BAK significantly reduced colony counts, compared with BAK or saline (P < 0.05). There were no differences between GAT+BAK and GAT without BAK for S. epidermidis. Conclusions: For the first time, we demonstrated that a preservative (0.005% BAK) significantly enhanced the antibacterial efficacy of an antibiotic (0.3%, GAT) in an experimental rabbit model of intrastromal keratitis.