Effects of amiloride on plasma and total body potassium, blood pressure, and the renin-angiotensin-aldosterone system in thiazide-treated hypertensive patients

Total body potassium content, plasma potassium concentration, blood pressure, and plasma concentrations of renin, angiotensin II, and aldosterone were measured in patients with essential hypertension after a run-in period of 8 wk on a regimen of hydrochlorothiazide (median dosage 75 mg/day). Patients were then randomly assigned to continued hydrochlorothiazide therapy (group I) or to receive adjunctive treatment with amiloride (group II, median dosage 15 mg/day or 5 mg per 25 mg hydrochlorothiazide) for the following 3 mo. There were no changes in group I patients during 3 mo on hydrochlorothiazide in plasma potassium, total body potassium content, or the renin-angiotensin-aldosterone system. Blood pressure was also unchanged. In group II patients addition of amiloride to hydrochlorothiazide induced a rise in plasma and total body potassium of approximately 15% and 4%. The potassium-retaining effect was maintained throughout the 12-wk period, although the maximal changes were observed after 8 wk of treatment. Supine blood pressure did not change, but there was a significant decrease in standing systolic blood pressure. There was a marked rise in plasma concentrations of renin, angiotensin II, and aldosterone.