Analysis of Chlorthalidone in Biological Fluids by High-Performance Liquid Chromatography Using a Rapid Column Cleanup Procedure

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Abstract
A high-performance liquid chromatographic assay usable for clinical monitoring of chlorthalidone in biological fluids was developed. Extraction efficiency was >80% for blood and urine using a rapid, disposable column cleanup procedure. Chlorthalidone could be reliably measured in the range of 100–4,000 ng/ml in biological fluids with excellent day-to-day reproducibility and within-day precision. Chlorthalidone was found to be stable at –20°C in blood and urine for at least 1 year, permitting repeat assays and large clinical studies to be conducted. The pharmacokinetics of chlorthalidone was studied in 24 subjects over a 120-h time interval following a single dose. Chlorthalidone has a long terminal half-life in whole blood of 49 h, with peak concentrations occurring 8–10 h after oral dosing. During the first 12 h after dosing, chlorthalidone was rapidly excreted into urine followed by a slower phase with a half-life of 49 h.