Development of an Effective and Cost-Saving Synergistic-Antibacterial Therapy for Prevention of Endophthalmitis

Background: Endophthalmitis, associated with intraocular procedures, is an infection of the eye that can rapidly result in substantial irreversible loss of vision and may even lead to removal of the eye. Prevention strategies vary globally and often include antibiotic use—often consisting of a broad-spectrum mono-therapeutic agent. The purpose of this study is to test the efficacy and value of combinations of cefuroxime (cefu), cefazolin (cefa), azithromycin (azith), and/or tobramycin (tob) as alternatives to the use of moxifloxacin. We looked for synergism since these antimicrobials used different mechanisms of inhibition. Methods: Initially, we examined individual antimicrobials to determine the minimal bactericidal concentrations (MBC) of each individual treatment against Klebsiella pneumonia, Pseudomonas aeruginosa, Staphylococcus aureus, two clinical isolates of MRSA, and Staphylococcus epidermidis, by both the Zone of Inhibition (ZOI) and the Colony Forming Unit (CFU) assays. We then used these data in a combinatorial study. Results: We found combinations that were synergistic against all the bacteria tested, resulting in total eradication [8 logs] of all bacteria. We found that the ZOI assay provided less consistent results than the CFU assays. Conclusions: We have found combinations of these antimicrobials that were synergistic in the total eradication (8 logs) of all bacteria tested. These three combinations were: cefuroxime/azithromycin; azithromycin/tobramycin; and cefuroxime/tobramycin. Moxifloxacin (Vigamox) did not completely eradicate Staphylococcus epidermidis. These combinations can then be used as eye drops to serve as a prophylactic for endophthalmitis after eye injections and eye surgery.