title: Immediate cardiovascular responses to oral prazosin--effects of concurrent beta-blockers.
abstract: Initiation of prazosin therapy may be complicated by the first-dose response of acute postural hypotension and tachycardia. The effects of beta-blocker on the responses to oral prazosin were studied in eight 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 (mean +/- SD), associated with a tachycardia of 117 +/- 13 bpm, and an increase in mean plasma norepinephrine concentration to 9.6 +/- 7.9 nmole/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 (BP) 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 dose of prazosin.
mesh_terms: D000284:Administration, Oral; D000319:Adrenergic beta-Antagonists / Q000008:administration & dosage / Q000494:pharmacology*; D000328:Adult; D001794:Blood Pressure / Q000187:drug effects*; D002395:Catecholamines / Q000097:blood; D004305:Dose-Response Relationship, Drug; D004359:Drug Therapy, Combination; D006339:Heart Rate / Q000187:drug effects*; D006801:Humans; D007024:Hypotension, Orthostatic / Q000139:chemically induced; D008297:Male; D011224:Prazosin / Q000008:administration & dosage / Q000009:adverse effects* / Q000097:blood; D011799:Quinazolines / Q000009:adverse effects*
chemical_list: D000319:Adrenergic beta-Antagonists; D002395:Catecholamines; D011799:Quinazolines; D011224:Prazosin