In vitro antibacterial spectrum of a new broad-spectrum 8-methoxy fluoroquinolone, gatifloxacin

The in vitro antibacterial spectrum of gatifloxacin was compared with those of ciprofloxacin and ofloxacin. Gatifloxacin was two- to four-fold more po tent than comparator quinolones against staphylococci, streptococci, pneumo cocci and enterococci (gatifloxacin MIC(90)s, less than or equal to 1 mg/L, except 4 mg/L against methicillin-resistant Staphylococcus aureus and Ente rococcus faecium). Gatifloxacin was two-fold less potent than ciprofloxacin , and the same as or two-fold more potent than ofloxacin against Enterobact eriaceae (MIC(90)s, 0.06-0.5 mg/L against most members of the Enterobacteri aceae and less than or equal to 1 mg/L against Proteus/Morganella spp.). Re lative to the comparator quinolones, gatifloxacin was two- to four-fold mor e potent against Providencia spp., and had good potency against Acinetobact er spp. (MIC(90)s, 0.25-1 mg/L). Gatifloxacin and ofloxacin had similar ant i-pseudomonal potency, with corresponding MIC(90)s of 4, 8 and 0.25 mg/L fo r Pseudomonas aeruginosa, Pseudomonas fluorescens and Pseudomonas stutzeri, while ciprofloxacin had two- to eight-fold more potency. The three quinolo nes were equipotent against Burkholderia cepacia (MIC(90)s, 8 mg/L), but ga tifloxacin was two-fold more potent against Stenotrophomonas maltophilia (M IC90, 4 mg/L). Gatifloxacin was highly potent (MIC(90)s, 0.03-0.06 mg/L) ag ainst Haemophilus influenzae, Legionella spp., Helicobacter pylori and had at least eight-fold better anti-chlamydial and anti-mycoplasma potency (gat ifloxacin MIC(90)s, 0.13 mg/L). The higher quinolone MICs for ureaplasma (M IC(90)s, 4-8 mg/L) may be due to the acidic pH of the ureaplasma test mediu m, which antagonizes quinolones. Like other quinolones, gatifloxacin had po or potency against Mycobacterium avium-intracellulare, though it was eight- to 16-fold more potent against Mycobacterium tuberculosis (MIC90, 0.25 mg/ L). Of the three quinolones, only gatifloxacin had activity against Bactero ides fragilis and Clostridium difficile. In summary, gatifloxacin is a broa d-spectrum 8-methoxy fluoroquinolone that is more potent than ciprofloxacin and ofloxacin against Gram-positive bacteria, chlamydia, mycoplasma, mycob acteria and anaerobes.