In vitro activity of fleroxacin in combination with other antimicrobial agents.

The trifluoroquinolone fleroxacin inhibits the majority of Enterobacteriaceae at concentrations < or = 1 micrograms/mL and most Pseudomonas aeruginosa and staphylococci at < or = 2 micrograms/mL. The purpose of this study was to determine the effect of the combination of fleroxacin with other antimicrobial agents. Previous studies that used checkerboard assay, fixed concentrations, and killing curves were reviewed, and these methods were used to evaluate the combination of fleroxacin and agents that had not been previously studied. The combination of fleroxacin with such aminoglycosides as gentamicin, amikacin, and tobramycin is indifferent against most Enterobacteriaceae, as is the combination of fleroxacin with penicillins, cephalosporins, rifampin, clindamycin, and metronidazole. Combinations of fleroxacin with penicillins, cephalosporins, imipenem, aminoglycosides, clindamycin, metronidazole, and rifampin are indifferent against P. aeruginosa. Fosfomycin and fleroxacin acted synergistically against P. aeruginosa. Against staphylococci, combinations of fleroxacin with oxacillin, rifampin, or fosfomycin had synergistic or additive effects, whereas combinations of fleroxacin with vancomycin, gentamicin, or metronidazole have shown indifference. No synergy or antagonism has been found for combinations of fleroxacin with penicillin, vancomycin, erythromycin, clindamycin, or rifampin against streptococci or enterococci. The combination of fleroxacin and metronidazole has proved synergistic against various Bacteroides species. In general, combinations of fleroxacin with other antimicrobial agents display indifference and rarely synergy. Thus, fleroxacin can be combined with other antibiotics to enlarge the spectrum of activity.