Spectrofluorometric determination of hydroflumethiazide in plasma and urine

A rapid, accurate, sensitive, and reproducible assay for hydroflumethiazide in plasma and urine was developed after studies of its UV and fluorescence spectral properties and partitioning behavior. The assay is based on initial extraction from acidified plasma or urine into ether, back-extraction into basic solution followed by acidification to about pH 1, and measurement of the fluorescence derived from the unionized molecule. Analysis of variance indicated no significant differences in assays performed on the same day. The mean recovery was 98.8 +/- 7.4% for plasma over a concentration range of 0.2-2.0 mug/ml. The method is convenient for routine clinical use and has sufficient sensitivity to quantify hydroflumethiazide levels after administration of therapeutic doses.