High-performance liquid chromatographic analysis of theophylline in serum and its use in therapeutic drug monitoring.

A rapid, highly sensitive high-performance liquid chromatographic method has been developed for the determination of theophylline in serum using beta-hydroxyethyltheophylline as an internal standard (IS). Theophylline and IS were extracted from serum using a mixture of dichloromethane: isopropanol (90: 10, v/v) and eluted from a 5 microns, C-18 reversed-phase column at 60 degrees C with a mobile phase consisting of sodium acetate buffer-acetonitrile (90:10, v/v), at a flow rate of 1 ml/min with ultraviolet detection at 280 nm. Each analysis required no longer than 7 min to perform. Quantification was achieved by the measurement of the peak: height ratio and the relative and absolute recoveries varied from 86 to 100%. Within-day coefficients of variation ranged from 2.9 to 5.1% and between-day coefficients of variation from 1.1 to 5.9% in subtherapeutic, therapeutic, and toxic concentrations.