Simultaneous assay of fluoroquinolones and theophylline in plasma by high-performance liquid chromatography.

A sensitive and selective reversed-phase high-performance liquid chromatographic method for the determination of theophylline in plasma simultaneously with either ciprofloxacin, enoxacin or norfloxacin has been developed. It involves extraction of plasma with chloroform-isopropanol or dichloromethane-isopropanol prior to chromatography on a Spherisorb ODS2 column. The mobile phase is 15% acetonitrile in a phosphate buffer (pH 3.0) containing tetrabutylammonium hydrogen sulphate (4.4 mM) as an ion-pairing agent. Ultraviolet detection is carried out at 280 nm. Run time is less than 10 min for all three separations. The assays have been used to determine the effect of plasma concentrations of fluoroquinolone on theophylline clearance.