A comparison of the effect of lisinopril and hydrochlorothiazide on electrolyte balance in essential hypertension.

The effects of lisinopril 10-20 mg or hydrochlorothiazide 25-50 mg (each given once daily) on blood pressure, serum sodium, potassium and magnesium concentrations, total body potassium and urinary cation excretion were compared in a group of hypertensive patients using a double blind randomised crossover design. Each active treatment phase lasted six weeks and a total of sixteen patients completed the study. Both lisinopril and hydrochlorothiazide produced clinically significant decreases in blood pressure. However, lisinopril treatment produced a mean reduction of 14 mmHg in sitting diastolic pressure compared with a 7 mmHg reduction for hydrochlorothiazide treatment. This difference was statistically significant. The decrease in the concentration of serum potassium during hydrochlorothiazide treatment was greater than that during lisinopril treatment (0.53 vs 0.01 mmol.1). The absolute value of serum potassium was significantly lower on hydrochlorothiazide than on lisinopril therapy. Neither treatment had an effect on serum magnesium concentrations, nor was there any significant effect of either treatment on urine volume or urinary excretion of sodium, potassium or magnesium. There was a trend towards increased total body potassium concentration on lisinopril compared with a decrease in total body potassium on hydrochlorothiazide. However, this difference was just outside the range of statistical significance. Both treatments were equally well tolerated. The results indicate slight superiority of lisinopril over hydrochlorothiazide with regard to control of diastolic blood pressure with a better effect on overall electrolyte balance.