Synergy of fluoroquinolones with other antimicrobial agents.

Synergy resulting from the combination of ciprofloxacin and an antipseudomonal penicillin has been reported for 20%-50% of isolates of Pseudomonas aeruginosa. A similar effect has also been reported for the combination of ciprofloxacin and fosfomycin. In contrast, the combination of quinolones and aminoglycosides rarely showed synergy when tested against P. aeruginosa. Most studies have shown that the combination of beta-lactams or aminoglycosides with quinolones is indifferent against Escherichia coli, Klebsiella species, Enterobacter species, Citrobacter species, and Serratia species. The combination of ciprofloxacin and chloramphenicol can be antagonistic against E. coli. In general, the combination of quinolone antibiotics with other drugs tested against staphylococci, enterococci, and anaerobic species has shown indifference. The neutropenic mouse model of infection has demonstrated the synergistic effect of ciprofloxacin plus antipseudomonal penicillins; the combination of ciprofloxacin and rifampin has been superior to single agents in experimental Staphylococcus aureus osteomyelitis. Ciprofloxacin has been the quinolone studied most thoroughly, and few data are available about the combination of other quinolones with other antimicrobial agents. Overall, the occurrence of synergy when quinolones are combined with other antimicrobial agents is infrequent, and clinical studies that demonstrate the clinical relevance of data from in vitro and animal models of infection are not available. However, data from in vitro and animal model studies indicate that the combination of a quinolone with other antimicrobial agents rarely results in antagonism.