A-80556 is a novel
fluoroquinolone with potent antibacterial activity against gram-positive, gram-negative, and anaerobic organisms.
A-80556 was more active than
ciprofloxacin,
ofloxacin,
lomefloxacin, and
sparfloxacin against gram-positive bacteria.
A-80556 was particularly active against Staphylococcus aureus (MIC for 90% of isolates [MIC90], 0.12 microgram/ml, relative to
fluoroquinolone-susceptible strains) and Streptococcus pneumoniae (MIC90, 0.12 microgram/ml).
A-80556 was also the most active of the
quinolones tested against
ciprofloxacin-resistant S. aureus, with an MIC90 of 4.0 micrograms/ml; that of
ciprofloxacin was > 128 micrograms/ml. However, the significance of this activity is not known.
A-80556 was slightly less active against Escherichia coli (MIC90, 0.06 microgram/ml) and other enteric organisms than
ciprofloxacin (MIC90 for E. coli, < or = 0.03 microgram/ml).
A-80556 was slightly less active against Pseudomonas aeruginosa (MIC90, 4.0 micrograms/ml) than
ciprofloxacin (MIC90, 2.0 micrograms/ml) and more active against Acinetobacter spp. (respective MIC90s, 0.12 and 0.5 microgram/ml).
A-80556 was also the most active compound against anaerobes. Against Bacteroides fragilis, the MIC90 of
A-80556 was 2.0 micrograms/ml; that of
ciprofloxacin was 16 micrograms/ml. The in vivo efficacy of
A-80556 in experimental models with both gram-positive and gram-negative
infections was consistent with the in vitro activity and pharmacokinetics and oral absorption in mice.