Ophthalmic antibiotics and antimicrobial resistance a randomized, controlled study of patients undergoing intravitreal injections.

Purpose: To determine whether repeated exposure of ocular and nasopharyngeal flora to ophthalmic antibiotics promotes antimicrobial resistance in patients undergoing intravitreal injections for choroidal neovascularization (CNV).

Design: Prospective, randomized, controlled, clinical trial.

Participants: Forty-eight eyes of 24 patients undergoing unilateral intravitreal injections for CNV.

Methods: Patients were assigned randomly to 1 of 4 ophthalmic antibiotics (azithromycin 1%, ofloxacin 0.3%, gatifloxacin 0.3%, moxifloxacin 0.5%) to be used after each injection in the treatment eye only. Bilateral conjunctival and unilateral nasopharyngeal cultures on the treatment side were obtained at baseline and were repeated at each subsequent visit for 1 year. All bacterial isolates were tested for antibiotic susceptibility to 16 different antibiotics using the Kirby-Bauer disc diffusion technique. Genetic analysis of bacteria strains was performed using pulse-field gel electrophoresis.

Main Outcome Measures: Changes in antibiotic susceptibility patterns of conjunctival and nasopharyngeal flora over time and emergence of resistant strains.

Results: Eight subjects (33%) grew Staphylococcus aureus from the nasopharynx and 1 subject (13%) showed emergence of a resistant strain. Coagulase-negative staphylococci (CNS) cultured from eyes repeatedly exposed to fluoroquinolone antibiotics demonstrated significantly increased rates of resistance to third- and fourth-generation fluoroquinolones compared with untreated eyes. Resistance to ofloxacin and levofloxacin was roughly 85% (P = 0.003), and resistance to gatifloxacin and moxifloxacin approached 67% (P = 0.009) and 77% (P<0.001), respectively. In contrast, CNS isolated from eyes repeatedly exposed to azithromycin demonstrated significantly increased resistance (94%) to erythromycin and azithromycin when compared with control eyes (P = 0.009) and decreased resistance to third-generation (P<0.03) and fourth-generation (P<0.001) fluoroquinolones when compared with eyes exposed to fluoroquinolones.

Conclusions: Repeated exposure of ocular and nasopharyngeal flora to ophthalmic antibiotics selects for resistant strains.