Mode of Action: The quinolones inhibit bacterial enzyme topoisomerases, including topoisomerase II and topoisomerase IV, otherwise known as DNA-gyrase. Topoisomerases support supercoiling and subsequent uncoiling of DNA so that the DNA can twist into the chromosomal domains that conform to the RNA core. The quinolones are usually bactericidal; susceptible organisms lose viability within 20 min of exposure to optimal concentrations of the newer fluoro-quinolones. Quinolones are associated with a post- antibiotic effect in a number of bacteria, principally gram-negative (eg, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa). The effect generally lasts 4-8 hr after exposure.

Efficacy of the fluorinated quinolones depends on concentrations in plasma that exceed the MIC of the infecting organism by 10- to 12- fold.