Blood pressure lowering and potassium conservation by triamterene-hydrochlorothiazide and amiloride-hydrochlorothiazide in hypertension

Effects of once-daily doses of 50 mg triamterene with 25 mg hydrochlorothiazide and 5 mg amiloride with 50 mg hydrochlorothiazide were compared in a randomized, multicenter study of 84 adult subjects with mild to moderate hypertension (diastolic blood pressure 90 to 114 mm Hg). After a 3-wk placebo lead-in period, the subjects entered a 6-wk treatment period. The two drug regimens were compared with respect to antihypertensive effects and effects on serum potassium and magnesium levels during the final week of drug therapy, with the use of the last week of placebo therapy as a covariate. Both drug regimens substantially reduced mean supine systolic and diastolic blood pressures to well within normal limits; there was no significant difference between the two groups. Twenty-four of the 41 subjects receiving triamterene-hydrochlorothiazide (59%) and 29 of the 43 patients receiving amiloride-hydrochlorothiazide (67%) had diastolic blood pressure <90 mm Hg at week 9. Five subjects receiving amiloride-hydrochlorothiazide (12%) and two subjects receiving triamterene-hydrochlorothiazide (5%) had hypokalemia (serum potassium level <3.5 mEq/l) at week 9. The average decrease in serum potassium levels during amiloride-hydrochlorothiazide therapy (−0.33 ± 0.08 mEq/l) was greater than that after triamterene-hydrochlorothiazide (−0.08 ± 0.07 mEq/l). Serum magnesium levels were not changed by either regimen. Weight loss was greater in the amiloride-hydrochlorothiazide group than in the triamterene-hydrochlorothiazide group. It is reasonable to assume that the greater potassium loss during amiloride-hydrochlorothiazide therapy than during triamterene-hydrochlorothiazide therapy was a consequence of the larger dose of hydrochlorothiazide in the former (50 mg) compared with the latter (25 mg). Although the effect on lowering blood pressure by amiloride-hydrochlorothiazide was slightly greater than that by triamterene-hydrochlorothiazide (also consistent with the larger dose of hydrochlorothiazide), the difference was small and not significant. Triamterene-hydrochlorothiazide at low doses is effective in the treatment of hypertension. Clinical Pharmacology and Therapeutics (1985) 37, 61–65; doi:10.1038/clpt.1985.12