Gatifloxacin (CG5501) 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.

Topo II:36.7 μM (IC50)

Gatifloxacin increases serum adrenaline levels in both normal and diabetic rats, and concurrently reduces serum glucose concentrations in these subjects.

Gatifloxacin exhibits potent inhibitory activity against bacterial type II topoisomerases, with half-maximal inhibitory concentrations (IC50) of 13.8 mg/mL and 0.109 mg/mL for Staphylococcus aureus topoisomerase and Escherichia coli DNA gyrase, respectively. Its inhibitory effect on HeLa cell topoisomerase II is minimal, with an IC50 of 265 mg/mL. Gatifloxacin inhibits Mycobacterium tuberculosis ATCC 35801 with a minimum inhibitory concentration (MIC) of 0.125 μg/mL. When used in combination with ciprofloxacin, gatifloxacin demonstrates a synergistic effect on 19% of 31 strains of Pseudomonas aeruginosa. However, gatifloxacin's activity is two-fold lower than that of ciprofloxacin and two-fold less potent than ofloxacin against Enterobacteriaceae. Gatifloxacin shows strong antimicrobial activity against Haemophilus influenzae, Legionella, and Helicobacter pylori (MIC90s, 0.03-0.06 mg/L), and at least an eight-fold greater efficacy against Chlamydiaceae and Mycoplasmataceae (gatifloxacin MIC90s, 0.13 mg/L).