Uptake and intracellular activity of fleroxacin in phagocytic cells

The uptake and intracellular activity of fleroxacin in murine J774.1 macrophages and human polymorphonuclear leukocytes were studied. The uptake of fleroxacin by J774.1 macrophages was rapid and reversible. The cellular to extracellular concentration ratios of fleroxacin in both types of phagocytes ranged from 5 to 6. These ratios were almost equal to those of ofloxacin and ciprofloxacin, and higher than those of the beta-lactam antibiotics, flomoxef and piperacillin. The intracellular activity of fleroxacin in J774.1 macrophages, examined with Staphylococcus aurenus as a test bacterium, showed that its bactericidal action was dependent on both the extracellular concentration and the exposure time. Fleroxacin reduced the number of viable cells of ingested S. aureus at an extracellular concentration that simulated the clinical serum levels, that is, killing more than 70% of the bacteria at 4 micrograms/ml. The bactericidal activity of fleroxacin in phagocytes was superior to that of erythromycin, flomoxef and piperacillin. These results indicate that fleroxacin is taken up well by phagocytes, reaching a concentration several fold higher than the extracellular concentration, and that it has potent activity against intracellular pathogens.