Fully automated high-performance liquid chromatography of ciprofloxacin with direct injection of plasma and Mueller-Hinton broth for pharmacokinetic/pharmacodynamic studies.

An isocratic high-performance liquid chromatographic method with column switching and direct injection has been developed to determine ciprofloxacin in plasma and Mueller-Hinton broth. An on-line dilution of the sample was performed with a loading mobile phase consisting of 173 mM phosphoric acid. The analyte was retained on a LiChrocart 4-4 precolumn filled with a LiChrospher 100 RP18, 5 microm. An electric-actuated system with two six-port valves allowed a clean-up step with a mixture 20 mM phosphate buffer (pH 3.5)-methanol (97:3, v/v) and the transfer of the analyte by a back-flush mode to a 150 x 4.6 mm I.D. column packed with a Kromasil C8 5 microm, using a mobile phase of 20 mM phosphate buffer (pH 3.5)-acetonitrile (85:15, v/v). Fluorescence detection allowed a quantification limit of 0.078 microg/ml with a 40-microl sample size. The method was evaluated to determine its usefulness in studying the pharmacokinetic/pharmacodynamic behaviour of ciprofloxacin in an in vitro model.