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T. Das, A. Lall, A. Duggirala, S. Sharma, V.D. Rao; Are Fluoroquinolones Synergistic in Combination With Vancomycin, Amikacin, and Ceftazidime? Possible Implication in Treatment of Bacterial Endophthalmitis . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4887.
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Purpose: We evaluated the in vitro antibacterial efficacy of fluoroquinolones in combination with other commonly used intravitreal antibiotic. Systemic fluoroquinolones in combination with intravitreal antibiotics may prove efficacious in the treatment of selected cases of infective bacterial endophthalmitis. Methods: Staphylococcus epidermidis, Pseudomonas aeruginosa and Bacillus cereus, isolated from the vitreous of postoperative endophthalmitis patients, after proper characterization, were selected for the study. Synergism testing (NCCLS broth dilution susceptibility methods) was done for the combination of fluoroquinolones (ciprofloxacin and gatifloxacin) with the commonly used intravitreal antibiotics (vancomycin, amikacin, and ceftazidime). Two dimensional, two–agent checkerboard broth microdilution method was used with positive and negative controls. Six combinations of antibiotics for each bacterial isolate were tested. Each one had 70 different combinations of antibiotic concentration from 2–4 fold of the expected MIC to 1/8 – 1/16 of expected MIC. Time kill assay was done to reconfirm the results of broth microdilution. Results: There was no synergism of fluoroquinolones with other antibiotics for Staphylococcus epidermidis and Bacillus cereus. Synergism of ciprofloxacin and amilkacin was seen for Pseudomonas aeruginosa as follows: complete synergism– ciprofloxacin ¼ MIC + amikacin ¼ MIC; partial synergism– ciprofloxacin ½ MIC+ amikacin 1/16 MIC or ciprofloxacin 1/16 MIC + amikacin ½ MIC. Time kill assay confirmed the synergistic activity of ciprofloxacin and amikacin, apparent at as early as 4 hours and maintained thereafter. Conclusions: Fluoroquinolones are highly active against gram–negative bacteria and have intermediate or no activity against gram+ve bacteria. Synergism of ciprofloxacin and amikacin may play a role in culture proven gram–negative infection particularly with Pseudomonas.
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