Interactions of ciprofloxacin with clindamycin, metronidazole, cefoxitin, cefotaxime, and mezlocillin against gram-positive and gram-negative anaerobic bacteria.

A total of 598 clinical isolates of anaerobic bacteria were tested against ciprofloxacin by the agar dilution technique with 10(5) CFU on Wilkins-Chalgren medium. Selected strains representative of the six major genera of anaerobes relatively resistant to the quinolones were tested for interactions with ciprofloxacin in combination with clindamycin, metronidazole, cefoxitin, cefotaxime, or mezlocillin by using a checkerboard agar dilution technique. Cefotaxime-ciprofloxacin and clindamycin-ciprofloxacin were the most effective combinations, with 16% of all isolates and 44% of the Bacteroides fragilis group isolates responding synergistically to the former combination and 9% of all isolates and 37% of Peptostreptococcus isolates responding synergistically to the latter. Occasional synergy was seen with all other antibiotic combinations except for metronidazole-ciprofloxacin. Likewise, synergism was seen with all groups of anaerobes except for Fusobacterium species. Antagonistic interactions were observed only with a Peptostreptococcus intermedius strain tested against clindamycin-ciprofloxacin. These data suggest that combinations of ciprofloxacin with these agents may be useful for certain resistant anaerobic infections.