Antihypertensive and Biochemical Effects of Different Doses of Hydrochlorothiazide Alone or in Combination with Triamterene

. The antihypertensive and biochemical effects of 25 mg hydrochlorothiazide alone or 50 mg hydrochlorothiazide alone or in combination with triamterene (either 37.5 or 75 mg) once daily were studied in 26 patients with essential hypertension. After a 5-week run-in period the patients were randomized to receive active therapy in a cross-over manner. Each treatment period lasted 3 months. All drugs significantly (p < 0.01) lowered both systolic and diastolic blood pressure. There were no differences in blood pressure between the medication periods. Serum potassium concentration was slightly lower during all medication periods than during the run-in period. This change was statistically significant (p < 0.01) only on 50 mg hydrochlorothiazide daily. There were no significant changes in serum magnesium during any of the periods compared to the run-in period. The lowest values were recorded on 50 mg hydrochlorothiazide alone and the highest on 50 mg hydrochlorothiazide plus 75 mg triamterene daily. A slight increase in serum urate was recorded in all medication periods compared to the run-in period. No significant changes were observed in serum total cholesterol, HDL cholesterol or triglycerides between any of the periods. It can be concluded that 25 mg of hydrochlorothiazide is as effective in lowering blood pressure as higher doses of the diuretic. Higher doses of thiazides will in some patients cause adverse metabolic reactions of which the fall in serum potassium and magnesium is effectively hindered by triamterene.