Antimicrobial resistance and ophthalmic antibiotics: 1-year results of a longitudinal controlled study of patients undergoing intravitreal injections.

OBJECTIVE

To determine antibiotic susceptibility patterns of conjunctival flora from patients undergoing intraocular injection for choroidal neovascularization after repeated exposure to ophthalmic antibiotics.

METHODS

We conducted a randomized, controlled, longitudinal study of 48 eyes of 24 patients undergoing unilateral intraocular injection for choroidal neovascularization. Bilateral conjunctival cultures from the treated eye and untreated (control) fellow eye were taken at baseline and after each injection (before the application of povidone-iodine). Patients were randomized to ofloxacin, 0.3%; azithromycin, 1%; gatifloxacin, 0.3%; or moxifloxacin hydrochloride, 0.5% and used only their assigned antibiotic after each injection. Bacterial isolates were tested for antibiotic susceptibility to 16 different antibiotics, and analysis of bacteria DNA was performed using pulse-field gel electrophoresis. Main outcome measures included changes in antibiotic susceptibility patterns of conjunctival flora after 1 year.

RESULTS

Coagulase-negative staphylococci (CNS) cultured from eyes repeatedly exposed to fluoroquinolone antibiotics demonstrated significantly increased rates of resistance to older-generation (P = .002) and newer-generation (P < .01) fluoroquinolones. In contrast, CNS isolated from azithromycin-exposed eyes demonstrated significantly increased resistance to macrolides (95%; P < .001) and decreased resistance to older-generation (P = .03) and newer-generation (P < .001) fluoroquinolones. There were significant increases in multiple-drug resistance of CNS isolated from treated eyes, with 81.8% and 67.5% of isolates resistant to at least 3 (P = .01) and at least 5 (P = .009) antibiotics, respectively.

CONCLUSION

Repeated exposure of conjunctival flora to ophthalmic antibiotics selects for resistant strains.

APPLICATION TO CLINICAL PRACTICE: Repeated use of ophthalmic antibiotics after intraocular injection promotes the emergence of antimicrobial resistance.

TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT00831961.