Activity of levofloxacin and ciprofloxacin in combination with cefepime, ceftazidime, imipenem, piperacillin-tazobactam and amikacin against defferent P. aeruginosa phenotype and Acinetobacter spp.

BACKGROUND: Combination therapy is used to widen the antimicrobial spectrum, minimize toxicity and prevent the emergence of resistant mutants. METHODS: Synergy between levofloxacin or ciprofloxacin and ceftazidime, cefepime, imipenem, piperacillin-tazobactam and amikacin was evaluated by checkerboard assay with 55 strains and by time-kill curves with 8 strains of Pseudomonas aeruginosa and Acinetobacter spp. RESULTS: In the checkerboard assay, synergy and additivity were the most frequent effects observed among all the combinations against P. aeruginosa and Acinetobacter spp., with no significant differences between the two fluoroquinolones. No antagonism was observed. In the time-kill curves, synergy was evidenced against all the tested strains, at least for one combination at one of the time points considered. Levofloxacin and ciprofloxacin combined with ceftazidime, as well as levofloxacin plus amikacin, were synergistic for all the strains tested. CONCLUSION: Combinations of fluoroquinolones with beta-lactams or amikacin show an enhanced activity against P. aeruginosa and Acinetobacter spp.