Plasma potassium levels in hypertensive patients receiving fixed-combination diuretic therapy.

Among 54 patients attending a hospital hypertension clinic and receiving the fixed-combination diuretic Moduretic (hydrochlorothiazide 50 mg, amiloride 5 mg), there was a 44.4% incidence of hypokalaemia. The mean drop in plasma potassium level was 0.69 mmol/L (P less than 0.0001), the mean low level being 2.81 mmol/L. Seventy-four per cent of falls occurred within 52 weeks of the start of therapy, 19.5 weeks being the average period between a normal and a low plasma potassium level. There was no difference in the fall in potassium level between male and female subjects, and beta-blockers were not obviously protective, although there was a statistically significant smaller fall in potassium level in females treated with them. The clinical significance of the unexpected hypokalaemia is uncertain; but even with fixed-combination diuretics, it remains necessary to monitor the plasma potassium level regularly in order to avoid complicating situations. The results of the present study would cast doubt on the efficacy of 5 mg of amiloride with 50 mg of hydrochlorothiazide in fixed-combination form in preventing hypokalaemia in this clinical situation.