Clonidine, acebutolol and their interaction in essential hypertension: effects on blood pressure and the control of water and electrolyte balance.

The effects of 0.5 mg of slow-release (sr) clonidine, 800 mg of acebutolol, and of both drugs combined on blood pressure and the water-salt balance were compared in 10 patients with essential hypertension. An initial placebo period was followed by three 72-h periods during which 5 patients were given sr-clonidine, acebutolol plus sr-clonidine, and acebutolol, respectively in that order whereas the other 5 received the same drugs in the opposite order. Placebo and active medications were given once a day, and the recorded variables were measured 24 h after the last intake. Sr-clonidine, acebutolol and their combined administration reduced mean blood pressure by 23, 16 and 39 mmHg, respectively, indicating first, that single daily doses of sr-clonidine and/or acebutolol constitute satisfactory antihypertensive treatments and second, that the interaction of these drugs is additive. All three treatments reduced plasma renin activity significantly and similarly. A reduction in plasma and urinary aldosterone was observed with sr-clonidine, and a decrease in plasma noradrenaline with the combined treatment. Both water diuresis and natriuresis rose significantly during combined therapy. The additive antihypertensive effects of sr-clonidine and acebutolol might be due to the parallel inhibition observed in the renin and sympathetic systems, and to the increase in natriuresis.