In vitro activity of A-56619 and A56620, two new aryl-fluoroquinolone antimicrobial agents.

The in vitro antimicrobial activity of two new aryl-fluoroquinolone antibiotics, A-56619 and A-56620, was compared with those of norfloxacin and several other antibiotics against 448 bacterial isolates. A-56620 was the most active agent tested. The usual 90% MIC of A-56620 was less than or equal to 2 micrograms/ml, except for enterococci, gentamicin-resistant Serratia marcescens, and gentamicin-resistant Pseudomonas aeruginosa, for which the 90% MIC was 4 micrograms/ml. A-56619 and norfloxacin were generally severalfold less active than A-56620. Cross resistance was observed between the quinolone antibiotics and other unrelated antibiotic classes.