FIG. 2.

Comparative short-term kinetics of the accumulation of ciprofloxacin (left) and moxifloxacin (right) at two different extracellular concentrations (open symbols, 5 mg/liter; closed symbols, 17 mg/liter). All data are the mean ± SD of three experiments (for symbols without bars, the SD is smaller than the symbol size). Results are expressed as the ratio of the apparent cellular concentration of each quinolone to its extracellular concentration. Data obtained for each drug were fitted to a two-phase exponential association; regression parameters are as follows: ciprofloxacin, 5 mg/liter and R² = 0.987; ciprofloxacin, 17 mg/liter and R² = 0.992; moxifloxacin, 5 mg/liter and R² = 0.999; moxifloxacin, 17 mg/liter and R² = 0.991. The parameters best describe the biphasic character of the uptake of these two quinolones.