BACTERICIDAL ACTIVITY, MORPHOLOGICAL ALTERATIONS, AND SYNERGISTIC INTERACTIONS OF RUFLOXACIN, A NEW FLUOROQUINOLONE, ALONE AND IN COMBINATION WITH ITS N-DESMETHYLATE D-DERIVATIVE (MF-922)

The in vitro activity of rufloxacin, alone and in combination with its metabolite (MF 922) against common respiratory and urinary tract path ogens and anaerobes was assessed. No synergistic interaction between r ufloxacin and MF 922 was observed by the checkerboard technique agains t aerobic bacteria. When the time-kill system was employed, 24 synergi stic interactions were noted out of 30 tests performed (80%), of which 14 (100%) were with Enterobacteriaceae isolates, 2 with Moraxella cat arrhalis (50%), 4 with Haemophilus influenzae (100%), 2 with Staphyloc occus aureus (50%) and 2 with Streptococcus pneumoniae and Streptococc us fragilis (50%), Synergism was found with all Bacteroides fragilis i rrespectively of the method used. Rufloxacin alone or in combination w ith MF 922, at concentrations achieved in vivo, induced morphological alterations in all the pathogens analyzed with the exception of M. cat arrhalis and H. influenzae. Towards S. pyogenes and S. pneumoniae, the same levels of rufloxacin and MF 922 were capable of inducing only ba cteriostatic rather than bactericidal effect, followed by reversible m orphological modifications. The presence of 50% human serum in the tes t media did not affect the results.