Immediate cardiovascular responses to oral prazosin--effects of concurrent beta-blockers

Clin Pharmacol Ther. 1981 Mar;29(3):303-9. doi: 10.1038/clpt.1981.40.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Administration, Oral
  • Adrenergic beta-Antagonists / administration & dosage
  • Adrenergic beta-Antagonists / pharmacology*
  • Adult
  • Blood Pressure / drug effects*
  • Catecholamines / blood
  • Dose-Response Relationship, Drug
  • Drug Therapy, Combination
  • Heart Rate / drug effects*
  • Humans
  • Hypotension, Orthostatic / chemically induced
  • Male
  • Prazosin / administration & dosage
  • Prazosin / adverse effects*
  • Prazosin / blood
  • Quinazolines / adverse effects*


  • Adrenergic beta-Antagonists
  • Catecholamines
  • Quinazolines
  • Prazosin