Simultaneous determination of grepafloxacin, ciprofloxacin, and theophylline in human plasma and urine by HPLC

A specific and sensitive reversed-phase high-performance liquid chromatogra phic (HPLC) method has been developed and validated for the simultaneous de termination of grepafloxacin, ciprofloxacin, and theophylline in human plas ma and urine. This assay allows these drugs to elute and be resolved in a s ingle chromatogram at 280 nm, using a linear gradient. The procedure involv es liquid-liquid extraction. Separation was achieved on a C-18 reversed-pha se column. The quantification limits were 0.05 mg/L in plasma and 0.5 mg/L in urine for grepafloxacin and ciprofloxacin and 0.5 mg/L in plasma and uri ne for theophylline. Standard curves were linear (correlation coefficients >0.999) over the ranges 0.05 to 5 mg/L for grepafloxacin and ciprofloxacin in plasma, from 0.5 to 20 mg/L for theophylline in plasma, and from 0.5 to 500 mg/L for the three drugs in urine. The coefficients of variation for th e three drugs were less than 10% for within- and between-day analyses. The recoveries averaged 94.5% for theophylline, 93% for ciprofloxacin, 93.7% fo r grepafloxacin, and 95.1% for the internal standard (IS). The assay can be used for pharmacokinetic studies of these drugs, to investigate the intera ction of grepafloxacin and ciprofloxacin with theophylline, or for routine simultaneous monitoring of theophylline, grepafloxacin, and ciprofloxacin.