Kinetics of kill of bacterial conjunctivitis isolates with moxifloxacin, a fluoroquinolone, compared with the aminoglycosides tobramycin and gentamicin

Rudolph S Wagner¹, David B Granet², Steven J Lichtenstein³, Tiffany Jamison⁴, Joseph J Dajcs⁴, Robert D Gross⁵, Paul Cockrum⁴

¹New Jersey Medical School, Newark, NJ, USA; ²Ratner Children’s Eye Center, University of California – San Diego, La Jolla, CA, USA; ³University of Illinois College of Medicine at Peoria, Peoria, Illinois, USA; ⁴Alcon Research, Ltd, Fort Worth, TX, USA; ⁵Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, TX, USA

Purpose: To compare the kinetics and speed of kill of Streptococcus pneumoniae and Haemophilus influenzae on exposure to three topical ophthalmic antibiotic solutions.

Materials and methods: Bacterial conjunctivitis isolates of S. pneumoniae and H. influenzae were exposed to 1:1000 dilutions of moxifloxacin 0.5%, tobramycin 0.3%, gentamicin 0.3%, and water (control). At 15, 30, 60, 120, and 180 minutes after exposure, aliquots were collected, cells were cultured, and viable cell counts were determined using standard microbiological methods.

Results: Moxifloxacin achieved 99.9% kill (3-log reduction) at approximately 2 hours for S. pneumoniae and at 15 minutes for H. influenzae. Tobramycin and gentamicin did not achieve 3-log reduction of S. pneumoniae during the 180-minute study period. An increase in bacterial growth was noted for these isolates. Gentamicin took more than 120 minutes to achieve the 3-log reduction of H. influenzae and tobramycin did not reach the 3-log reduction of this pathogen during the 180-minute study period.

Conclusion: Moxifloxacin killed S. pneumoniae and H. influenzae in vitro faster than tobramycin and gentamicin, suggesting its potential clinical benefit as a first-line treatment for bacterial conjunctivitis to minimize patient symptoms and to limit the contagiousness of the disease.

Keywords: kinetics of kill, bacterial conjunctivitis, in vitro, Streptococcus pneumoniae, Haemophilus influenzae, fluoroquinolones, aminoglycosides