High-performance liquid chromatographic analysis of nalidixic acid and hydroxynalidixic acid in plasma with a dynamic anion-exchange system.

A rapid high-performance liquid chromatographic method has been developed for monitoring plasma level of patients treated intravenously with nalidixic acid. The major metabolite (in vitro also active) can be determined as well; 50 microliter plasma samples are sufficient. Use is made of a dynamic anion-exchange system. Different parameters such as adsorption of the surfactant cetrimide onto the column; pH and ionic strength of the eluent, and the critical micelle concentration of the surfactant in the eluent have been studied.