Repeated antibiotic exposure after intravitreal injection induces resistance

Emerging resistance of ocular flora to third- and fourth-generation fluoroquinolones has been recently documented; however, this is the first study to establish ophthalmic antibiotic use with resistance. Results from this study demonstrate that resistant strains in the conjunctiva emerge immediately after exposure to antibiotic and are maintained by periodic re-exposure.

This finding has considerable implications because conjunctival flora, particularly Coagulase-negative staphylococci, is a common cause of ocular infections.

For this study, researchers randomized 48 eyes of 24 patients undergoing unilateral intravitreal injections for choroidal neovascularization assigned to either azithromycin 1%, ofloxacin 0.3%, gatifloxacin 0.3%, or moxifloxacin 0.5%, which was used after each injection. Cultures were taken at baseline and at each visit during the subsequent year. Eight patients (33 percent) grew Staphylococcus aureus from the nasopharynx and 1 patient (13 percent) showed emergence of a resistant strain. Resistant strains in the conjunctiva emerged immediately after antibiotic exposure and were maintained by periodic re-exposure.

The authors conclude that these findings indicate the need for greater thought and rationale regarding the use of antibiotics after intraocular injection to reduce the emergence of antimicrobial resistance.