Interactions of the 4-quinolones with other antibacterials.

The effect of sub-inhibitory concentrations of 16 antibacterials on the bactericidal activity of the 4-quinolones nalidixic acid, ciprofloxacin and ofloxacin against Escherichia coli KL16 in nutrient broth was investigated. Sub-inhibitory concentrations of rifampicin, clindamycin, chloramphenicol, erythromycin or tetracycline antagonised the bactericidal activity of the 4-quinolones. Conversely, all seven aminoglycosides tested enhanced the bactericidal activity of the 4-quinolones whereas the cell wall antagonists, azlocillin, mezlocillin, ceftazidime and vancomycin had no effect on the bactericidal activity of the 4-quinolones.