Double-blind factorial trial of prindolol and hydrochlorothiazide in hypertension

The antihypertensive actions of the beta-adrenergic blocking agent, prindolol, and of the diuretic, hydrochlorothiazide, were analysed in a double-blind randomized 2 X 2 factorial trial in 16 patients. There were four eight-week phases in which patients received prindolol alone, hydrochlorothiazide alone, prindolol plus hydrochlorothiazide in combination, and no treatment. Both drugs were given in fixed doses: prindolol, 10 mg three times per day; hydrochlorothiazide, 50 mg per day. Blood pressure was measured weekly, alternately at the outpatient clinic and at home. Supine mean arterial pressure (MAP) in resting patients fell from 127 mm Hg in the placebo phase to 117 mm Hg with hydrochlorothiazide alone, 116 mm Hg with prindolol alone, and 111 mm Hg with the combination of prindolol and hydrochlorothiazide. (The standard error of difference between treatments was +/-3-58). A mean factorial effect of -7 mm Hg for hydrochlorothiazide (P less than 0-01) and -8 mm Hg for prindolol (P less than 0-01) was obtained, and the two drugs acted in an additive manner. The effects on standing blood pressure in resting patients were similar. No serious side effects were noted.