Short term effects and urinary excretion of the new diuretic,indapamide, in normal subjects

Summary The pharmacology, toxicology and kinetics of a new diuretic indapamide, have been studied in six normal volunteers following a single oral dose of 40 mg. Pronounced diuresis was found, commencing three hours after ingestion, with a peak urinary flow at four to six hours, and continuing for a total of thirty-six hours. A fall in systolic standing blood pressure occurred twenty four hours after ingestion, coincident with the period of maximum dehydration. Free water clearance rose, accompanied by increased urinary losses of Na⁺, K⁺ and Cl^– and alkalinisation of the urine comparable to the actions of benzothiadiazines. Total urinary losses of Ca²⁺, Mg²⁺ and PO ₄ ^3– rose in spite of a fall in urinary concentrations of these ions. The Ca²⁺ effect compares with the acute ionic effects of other diuretics. No renal, hepatic or haematological toxic effect was demonstrated. The blood sugar level was not disturbed. Serum uric acid rose to abnormal levels although the change did not reach statistical significance. — A thin layer chromatographic method, with a sensitivity limit of 0.1 µg/ml., has been developed for the assay of indapamide in urine. The urinary excretion rates of the volunteers measured over forty-eight hours indicate that the drug is rapidly absorbed with a peak excretion, 2.9±1.3 µg/min occurring three hours after ingestion. The drug is eliminated bi-phasically with an initial short rapid elimination followed by a slower exponential decline with a mean elimination half-life of 10.3 ± 3.9 h. The mean urinary excretion of unchanged indapamide over forty-eight hours was 4.4±1.4% of the administered dose. — It is concluded that indapamide is an effective long-acting diuretic with comparable action to the benzothiadiazine diuretics, but without an effect on blood sugar level in single doses in normal subjects. In contrast with other diuretics, indapamide appears to be extensively metabolised in man, and its longer duration of action to be related to a longer elimination half-life.