Ciprofloxacin in combination with metronidazole

Ciprofloxacin has a reduced activity against anaerobic pathogens. Therefore, a combination of ciprofloxacin with an antimicrobial agent active against anaerobes, such as metronidazole, seems to be interesting for the treatment of mixed aerobic/anaerobic infections. High metronidazole concentrations (10 mg/l or 40 mg/l) neither affected the bactericidal efficacy of ciprofloxacin on aerobic pathogens, such as Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Enterococcus faecalis, nor on the anaerobic pathogens Clostridium perfringens and Clostridium difficile, as demonstrated by kill-kinetic curves. The same high concentrations, as well as lower therapeutically achievable concentration (2 mg/l or 5 mg/l) of metronidazole in combination with ciprofloxacin were slightly more potent for the tested clostridia than ciprofloxacin or metronidazole alone.