Dexamethasone Improves Ofloxacin Efficacy in Treating Acute Bacterial Conjunctivitis: Evidence from A Rabbit Model

Background: Bacterial conjunctivitis represents the major part of infectious conjunctivitis and, although it generally shows a spontaneous resolution, antibiotics speed the elimination of bacteria from the conjunctiva thus limiting the duration of the disease. The addition of anti-inflammatory drugs may potentiate the effectiveness of antibiotics in eradicating bacterial conjunctivitis. Aim of the present study is to compare the efficacy of two different eye drops based on ofloxacin without or with dexamethasone against bacterial conjunctivitis induced by Staphylococcus aureus or Pseudomonas aeruginosa. Methods: S. aureus or P. aeruginosa were inoculated in the palpebral conjunctiva of New Zealand rabbits. Twenty-four hours after bacteria inoculation, rabbits started treatment with eye drops containing saline, 0.3% ofloxacin or 0.3% ofloxacin/0.1% dexamethasone (5 times a day for 3 days). Animals were evaluated for pathology at specific times post infection using a clinical score. Tear levels of two inflammatory cytokines, interleukin (IL)-6 and (TGF)-ß, were quantified by ELISA. Results: Saline-treated rabbits showed a slow regression of the infection that was still present 96 hours after bacteria inoculation. On the contrary, in ofloxacin-treated rabbits, infective processes completely disappeared 72 hours after starting the treatment with a major efficacy of ofloxacin eye drops added with dexamethasone. Ofloxacin eye drops also reduced the infection-induced increase in tear levels of IL-6 and TGF-ß with greater effectiveness in the presence than in the absence of the corticosteroid. Conclusion: The addition of dexamethasone to ofloxacin results in a significative reduction of the bacterial infection indicating that the combination of a fluoroquinolone with a corticosteroid may accelerate disease resolution thus helping to minimize the potentially dangerous effects of bacterial conjunctivitis. Although results in animals cannot be directly translated to humans, the stringency of the rabbit model proposed here to the human disease supports the translatability of these findings to clinical settings.