Benzalkonium chloride enhances the antibacterial efficacy of gatifloxacin in an experimental rabbit model of intrastromal keratitis.
OBJECTIVE
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 reduced 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.
Romanowski
Eric G
EG
The Charles T. Campbell Ophthalmic Microbiology Laboratory, University of Pittsburgh Medical Center, Pittsburgh, PA 15213, USA. romanowskieg@upmc.edu
Mah
Francis S
FS
Kowalski
Regis P
RP
Yates
Kathleen A
KA
Gordon
Y Jerold
YJ
D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage*; D001548:Benzalkonium Compounds / Q000008:administration & dosage*; D003319:Corneal Stroma / Q000187:drug effects / Q000382:microbiology*; D004195:Disease Models, Animal; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D015818:Eye Infections, Bacterial / Q000188:drug therapy* / Q000382:microbiology; D005260:Female; D024841:Fluoroquinolones / Q000008:administration & dosage*; D000077734:Gatifloxacin; D007634:Keratitis / Q000188:drug therapy* / Q000382:microbiology; D011817:Rabbits; D013203:Staphylococcal Infections / Q000188:drug therapy* / Q000382:microbiology
D000900:Anti-Bacterial Agents; D001548:Benzalkonium Compounds; D024841:Fluoroquinolones; D000077734:Gatifloxacin