Initial potassium loss and hypokalaemia during chlorthalidone administration in patients with essential hypertension: the influence of dietary sodium restriction

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Abstract
To investigate the initial K loss and development of hypokalemia during the administration of an oral diuretic, metabolic balance studies were performed in 10 patients with essential hypertension who showed hypokalemia under prior oral diuretic treatment. Chlorthalidone (50 mg daily) was given for 14 days. Six patients received a normal Na diet and 4 a low Na (17 mmol/day) diet. All patients had a normal initial total body K (40K). The electrolyte balances, weight, bromide space, plasma renin activity and aldosterone secretion rate were measured. In both groups a K deficit developed, with proportionally larger losses from the extracellular than from the intracellular compartment. In the normal Na group the highest mean K deficit was 176 mmol on day 9, after which some K was regained; in the low Na group the highest deficit was 276 mmol on day 13. The normal Na group showed an immediate but temporary rise of the renin and aldosterone levels; in the low Na group renin and aldosterone increased more slowly but remained elevated. Dietary Na restriction increases diuretic-induced dietary K loss, presumably by an increased activity of the renin-angiotensin-aldosterone system, while Na delivery to the distal renal tubules remains sufficiently high to allow increased K secretion.