Post-antibiotic and synergic effects of fluoroquinolones and ceftazidime in combination against Pseudomonas strains.

Infectious complications are still the leading cause of morbidity and mortality in seriously ill patients [1-3]. To combat the resistance of (mainly Gram-negative, non-fermentative) bacteria, e.g. Pseudomonas aeruginosa, to a wide spectrum of antibiotics, drug combination therapy has been widely adopted as standard clinical practice since the late 1990s. beta-Lactam combinations are not optimal and the potential of nephrotoxicity and ototoxicity from aminoglycosides has caused clinicians to evaluate new possibilities, such as combinations of fluoroquinolones and beta-lactams. We examine here the synergic and post-antibiotic effects (PAEs) of ciprofloxacin, ofloxacin and pefloxacin-ceftazidime combinations against 6 clinical Pseudomonas isolates. The fluoroquinolone-ceftazidime combinations were not only synergic against Comamonas (P.) testosteroni, but had double the PAEs of the two drugs alone. The ciprofloxacin-ceftazidime combination had a longer PAE against P. aeruginosa isolate 1 than ciprofloxacin alone. The combinations, however, did not have longer PAEs than those of the single drugs against the other 5 P. aeruginosa isolates.