Fluorometric and high-performance liquid chromatographic measurement of quinolone uptake by human neutrophils

A fluorometric assay, based on the natural fluorescence of the quinolone nucleus, and high-performance liquid chromatography (HPLC) were compared to determine the penetration of six quinolones (norfloxacin, ciprofloxacin, ofloxacin, fleroxacin, lomefloxacin and temafloxacin) into human polymorphonuclear neutrophils (PMN). Intracellular concentrations after 20 min incubation of the cells with 10 and 25 mg/l were three or more times higher than the extracellular ones. There were no statistical differences between the two methods. At lower extracellular concentrations (2 and 5 mg/l) the intracellular levels of all the quinolones tested were undetectable by HPLC. Fluorometry is a useful method for determining the intracellular penetration of quinolones. The usefulness of HPLC, however, is questionable since it requires great volumes of cells and extracellular concentrations much higher than the therapeutic ones.