Absorption, metabolism, and excretion of hydrochlorothiazide

Abstract

¹⁴C-hydrochlorothiazide (hct) was administered orally (n = 4) and iv (n = 2) to healthy subjects. The gastrointestinal absorption ranged between 60% and 80%, most of it took place in the duodenum and the upper jejunum. The radioactivity was eliminated mainly in the urine, while no significant biliary excretion was observed. Chromatographic analysis of the urinary radioactivity demonstrated that >95% of the absorbed or injected ¹⁴C-hct was excreted unchanged. The radioactivity in plasma during the first 10 hr after oral administration declined with a fast phase but the levels of label thereafter suggested a slow phase. The existence of such a phase was verified in 1 subject given 75 mg hct orally. His plasma levels of hct (determined with gas-liquid chromatography) declined according to a 2-compartment model, the half-lives of the α− and β-phases being 1.7 and 13.1 hr, respectively. Hct accumulated in the blood cells and the ratio between the radioactivity in cells and that in plasma averaged 3.5. The fate of a single dose of ¹⁴C-hct in 2 hypertensive patients treated with the drug chronically was similar to that in the healthy subjects. A third patient, who had slightly elevated serum creatinine, eliminated hct more slowly than the others. Like the healthy subjects, the patients eliminated hct