In vitro activity: Gatifloxacin has somewhat better in vitro activity against M. tuberculosis than moxifloxacin, and both are much more active than levofloxacin. Gatifloxacin is against M. tuberculosis ATCC 35801 with MICs of 0.125 μg/mL. Gatifloxacin possesses potent inhibitory activities against bacterial type II topoisomerases (50% inhibitory concentration [IC50] = 13.8 mg/mL for S. aureus topoisomerase IV; IC50 = 0.109 mg/mL for E. coli DNA gyrase) but the lowest activity against HeLa cell topoisomerase II (IC50 = 265 mg/mL) among the quinolones tested. Gatifloxacin is synergic with the beta-lactams piperacillin, cefepime and meropenem, and with gentamicin against some drug-resistant pathogens. Gatifloxacin, an 8-methoxyfluoroquinolone, inhibits a staphylococcal efflux pump. Gatifloxacin combined with Ciprofloxacinplus shows synergy by the Etest method for 6 (19%) of the 31 P. aeruginosa isolates using a summation fractional inhibitory concentration of < or = 0.5 for synergy. Gatifloxacin is two-fold less potent than ciprofloxacin, and the same as or two-fold more potent than ofloxacin against Enterobacteriaceae. Gatifloxacin is highly potent (MIC90s, 0.03-0.06 mg/L) against Haemophilus influenzae, Legionella spp., Helicobacter pylori and has at least eight-fold better anti-chlamydial and anti-mycoplasma potency (gatifloxacin MIC90s, 0.13 mg/L).

Kinase Assay: Gatifloxacin is an antibiotic of the fourth-generation fluoroquinolone family, it inhibits the bacterial enzymes DNA gyrase and topoisomerase IV.

Cell Assay: Antibacterial Gatifloxacin is an antibiotic of the fourth-generation fluoroquinolone family, that like other members of that family, inhibits the bacterial enzymes DNA gyrase and topoisomerase IV. Gatifloxacin had activity equal to that of tosufloxacin and activity more potent than those of norfloxacin, ofloxacin, ciprofloxacin, and sparfloxacin against the second-step mutants (grlA gyrA; gatifloxacin MIC range, 1.56 to 3.13 microg/ml) and had the most potent activity against the third-step mutants (grlA gyrA grlA; gatifloxacin MIC range, 1.56 to 6.25 microg/ml), suggesting that gatifloxacin possesses the most potent inhibitory activity against singly mutated topo IV and singly mutated DNA gyrase among the quinolones tested. Ophthalmic gatifloxacin 0.3% is at least as effective as ciprofloxacin at healing corneal ulcers infected with Pseudomonas aeruginosa when gatifloxacin is administered less frequently than ciprofloxacin. Trends favored gatifloxacin in fluorescein retention scores.