SIMULTANEOUS ASSAY OF FLUOROQUINOLONES AND THEOPHYLLINE IN PLASMA BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY

A sensitive and selective reversed-phase high-performance liquid chrom atographic method for the determination of theophylline in plasma simu ltaneously with either ciprofloxacin, enoxacin or norfloxacin has been developed. It involves extraction of plasma with chloroform-isopropan ol or dichloromethane-isopropanol prior to chromatography on a Spheris orb ODS2 column. The mobile phase is 15% acetonitrile in a phosphate b uffer (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 assay s have been used to determine the effect of plasma concentrations of f luoroquinolone on theophylline clearance.