Prazosin alone and combined with a beta-adrenoreceptor blocker in treatment of hypertension.

We recorded intra-arterial ambulatory blood pressure in 13 patients with essential hypertension before and after long-term twice-daily prazosin therapy (mean dosage 13.8 mg, SD 4.2 mg). Nine other patients with essential hypertension inadequately controlled with beta-adrenoreceptor blocking drugs were studied before and after the addition of long-term twice-daily prazosin therapy (mean dosage 8.8 mg, SD 6.7 mg). Ten patients, responders from both groups, then received once-daily prazosin, and intraarterial monitoring was repeated for a third time. Circadian curves from pooled hourly data showed no significant reduction of intra-arterial ambulatory blood pressure with prazosin alone. There was a slight reflex tachycardia. Nine patients receiving combination therapy showed a daytime reduction in blood pressure averaging 24/6 mm Hg (p less than 0.001). Postural hypotension was recorded in both groups. Once-daily prazosin failed to control the blood pressure after 1700 h in the group of 10 patients defined as responders. Following combination therapy the blood pressure was reduced by 19/14 mm Hg at the peak of isometric hand grip and by 25/9 mm Hg on dynamic bicycle exercise. These data indicate that prazosin as an antihypertensive agent is best used in combination therapy with beta-adrenoreceptor blockade.