Comparative antihypertensive and endocrinologic effects of clonidine and prazosin in patients with essential hypertension.

The acute and chronic effects of fixed dosages of clonidine and prazosin on supine and upright blood pressure, the renin-angiotensin-aldosterone system, and plasma catecholamines were compared in 24 patients with essential hypertension. The patients were randomized into two groups; 11 received chlorthalidone (50 mg daily) throughout the protocol, but 13 received no diuretic. Clonidine was generally more effective in lowering systolic and diastolic blood pressure in the supine posture throughout the study; prazosin tended to decrease blood pressure in the upright posture more effectively, especially during the first week of treatment. The only truly significant difference was found after four weeks of treatment when the decrease in supine systolic blood pressure by clonidine of 26.5 +/- 8.9 mm Hg was greater than that of 1.7 +/- 5.6 mm Hg produced by prazosin (P less than .05).