Combination Effect of Cefuroxime and Levofloxacin Against Bacteria Isolated from the Healthy Conjunctival Sac and Endophthalmitis Cases Using a Fractional Inhibitory Concentration Index.

Abstract

Intracameral cefuroxime (CXM) and antibiotic eye drops such as fluoroquinolone are widely used for preventing endophthalmitis after cataract surgery. However, few reports are available regarding their interactions. This study was conducted to examine the in vitro interaction of CXM and levofloxacin (LVFX) against bacterial isolates from the healthy conjunctival sac before cataract surgery and from endophthalmitis cases. The activity of each drug was determined using a broth dilution method. Checkerboard synergy testing was performed for 43 isolates from the healthy conjunctival sac before cataract surgery and 15 isolates from endophthalmitis cases, respectively. Antimicrobial combinations were classified as synergistic, additive, indifferent, or antagonistic based on their fractional inhibitory concentration (FIC). Minimum inhibitory concentrations of CXM and LVFX against endophthalmitis isolates were compared against conjunctival sac isolates. The average FIC indices of combined CXM and LVFX used in endophthalmitis isolates were significantly lower than those in conjunctival sac isolates (P < 0.001). The synergistic activities of CXM and LVFX combinations were observed in 50% of endophthalmitis isolates and no conjunctival sac isolates. No consistent additive or synergistic effect was observed in Enterococcus faecalis isolates from endophthalmitis cases. CXM and LVFX resistance was frequently identified in the endophthalmitis isolates. However, CXM and LVFX combination showed a synergistic effect against endophthalmitis isolates and increased the antibiotic activity of each drug, suggesting that the combination may improve effects of both antibiotics and combat drug-resistant bacteria that cause endophthalmitis.