Immediate cardiovascular responses to oral prazosin—Effects of concurrent β-blockers

Abstract

Initiation of prazosin therapy may be complicated by the 1st dose response of acute postural hypotension and tachycardia. The effects of .beta.-blocker on the responses to oral prazosin were studied in 8 normotensive men. After 1 mg oral prazosin there was a marked postural fall in blood pressure to a lowest mean standing systolic pressure of 88 .+-. 7 mm Hg (.hivin.x [mean] .+-. SD), associated with a tachycardia of 117 .+-. 13 beats/min and an increase in mean plasma norepinephrine concentration to 9.6 .+-. 7.9 nmol/l. There was a linear relationship (r = 0.93) between plasma prazosin concentration and hypotensive effect. Concurrent propranolol 80 mg or primidolol 100 mg (a cardioselective .beta.-blocker) increased the severity and duration of the postural hypotensive response, with lowest mean systolic blood pressure of 79 .+-. 7 and 75 .+-. 9 mm Hg. There was no effect on the orthostatic release of norepinephrine but there was attenuation of the postural tachycardia. Concurrent .beta.-adrenergic blocking therapy, selective or nonselective, intensifies the immediate postural hypotensive response to the initial oral dose of prazosin.