Antihypertensive efficacy of two low dosages of hydrochlorothiazide in patients treated with captopril.

Twelve patients with essential hypertension (diastolic blood pressure, greater than 90 mmHg) after four weeks of treatment with captopril (50 mg BID) were randomly divided into two groups and treated with 12.5 mg and 25 mg of hydrochlorothiazide OD, in addition to captopril, in a crossover experimental design. Each dosage of hydrochlorothiazide was given for four weeks, with a two-week placebo washout period intervening. Both dosages of hydrochlorothiazide caused significant reductions in blood pressure. Eighty percent of patients achieved a diastolic blood pressure less than 90 mmHg during combination therapy, independent of the dose of diuretic. None of the patients reported significant side effects, and no changes were observed in routine biochemical analysis during treatment. In patients not completely controlled by captopril alone, a once-daily dosage of 12.5 mg of hydrochlorothiazide proved as effective as a 25-mg once-daily dosage. The smaller dosage could result in fewer unwanted metabolic effects induced by diuretic administration.