In vitro activities of amifloxacin and two of its metabolites.

Amifloxacin and two of its metabolites, N-desmethyl amifloxacin and amifloxacin N-oxide, were evaluated by a microdilution MIC susceptibility test against 500 clinical isolates and compared with ciprofloxacin, lomefloxacin, norfloxacin, aztreonam, and imipenem. Of the Staphylococcus species isolates, 208 were methicillin resistant; the MICs for 78 of the isolates of the family Enterobacteriaceae were greater than or equal to 64 micrograms of cefazolin, ampicillin, piperacillin, and mezlocillin per ml. Based on our results, amifloxacin had activity equivalent to those of norfloxacin and lomefloxacin but was less active than ciprofloxacin. The N-oxide metabolite was the least active; however, for the majority of gram-negative bacteria, N-desmethyl amifloxacin was as active as amifloxacin.