Xipamide and cyclopenthiazide in essential hypertension--comparative effects on blood pressure and plasma potassium

1 The blood pressure lowering effect of xipamide, a non-thiazide diuretic given for 6 weeks was compared in a randomised cross-over trial with that of cyclopenthiazide in 14 patients with essential hypertension. 2 Xipamide 10 or 20 mg given once daily was as effective in lowering supine blood pressure as daily cyclopenthiazide 0.5 mg. There was no difference in the blood pressure lowering effect of 10 mg xipamide daily for 2 weeks compared to 20 mg daily given for a further 4 weeks. 3 Plasma potassium was reduced by both drugs, but markedly more after both 10 mg and 20 mg xipamide than after cyclopenthiazide 0.5 mg. By the sixth week of treatment 13 of 14 patients on xipamide but only 6 of 14 on cyclopenthiazide has plasma potassium concentrations of, or less than, 3.5 mmol/l. The fall in plasma potassium was significantly greater and the final plasma potassium concentration was significantly lower after either dose of xipamide than after cyclopenthiazide. 4 These results suggest that 10 mg or 20 mg of xipamide daily is effective in lowering blood pressure in hypertensive patients but is associated with hypokalaemia. In view of recent evidence linking diuretic-induced hypokalaemia with cardiac dysrhythmias in patients with essential hypertension we would suggest that thiazide diuretics be used in preference to xipamide for the routine management of essential hypertension. Our results also suggest that the currently recommended dose of xipamide (20 mg) for the treatment of hypertension is excessive, and lower amounts than 10 mg per day might possibly be as effective in lowering blood pressure with less adverse metabolic consequences.