Antihypertensive Efficacy of Guanfacine and Prazosin in Patients with Mild to Moderate Essential Hypertension

Abstract

Guanfacine, an alpha 2 adrenoceptor agonist, was compared with prazosin hydrochloride for the treatment of patients with mild to moderate essential hypertension in an 8-week, double-blind, randomized, parallel evaluation to determine efficacy and safety. The study consisted of a 2-week screening/weaning period (phase I), a 3-week treatment period with chlorthalidone 25 mg every morning (phase II), and an 8-week double-blind treatment period with diuretic plus prazosin or guanfacine (phase III). Those who had an average seated diastolic blood pressure (BP) of 95 to 114 mm Hg at the end of the phase II period were eligible to enter the phase III period and were randomly assigned to chlorthalidone plus either guanfacine, 1 mg every night, or prazosin, 1 mg three times a day. Of the 102 patients who were randomly assigned to guanfacine or prazosin, 80% completed the entire study. Guanfacine and prazosin appeared to be equally effective and reduced seated as well as standing diastolic and systolic BP. The mean seated systolic and diastolic BP were reduced 11/9 mm Hg by guanfacine and 11/10 mm Hg by prazosin. The mean reduction in seated pulse was 3 beats/minute for guanfacine and no change with prazosin. Similar changes occurred in the standing position. Very few adverse effects were reported during the study. Adverse effects with an incidence of 5% or greater for either drug group were dizziness (6% guanfacine, 8% prazosin), xerostomia (6% guanfacine, 2% prazosin), and somnolence (0% guanfacine, 6% prazosin). Three patients (6%) in the prazosin group experienced symptoms of orthostasis requiring premature discontinuation of the drug and termination from the study.

Pharmacokinetics and pharmacodynamics of guanfacine extended release in adolescents aged 13–17 years with attention‐deficit/hyperactivity disorder

“…Consistent with guanfacine's known effects as an antihypertensive and similar to previous studies of guanfacine extended release, guanfacine extended release was associated with a dose‐dependent decrease in BP and HR. In this study, it was shown that the physiologic HR response to standing (i.e., an increase) is preserved during treatment with guanfacine extended release.…”

“…Guanfacine decreases blood pressure (BP) and heart rate (HR) through stimulation of α 2 ‐adrenoceptors in the brain stem . Several studies of adult subjects with mild to moderate hypertension have found that treatment with guanfacine (1–3 mg/day) significantly reduced both seated and standing systolic BP (SBP) and diastolic BP (DBP) as well as HR . Rebound hypertension and increases in HR have been noted upon rapid withdrawal of clonidine, another α 2 ‐adrenergic agonist, in hypertensive patients .…”

“…[1][2][3][4][5] Several studies of adult subjects with mild to moderate hypertension have found that treatment with guanfacine (1-3 mg/day) significantly reduced both seated and standing systolic BP (SBP) and diastolic BP (DBP) as well as HR. [6][7][8][9][10] Rebound hypertension and increases in HR have been noted upon rapid withdrawal of clonidine, another a 2 -adrenergic agonist, in hypertensive patients. 1,2,4,6,10 Less pronounced effects have been noted after treatment with guanfacine, although withdrawal symptoms remain an important clinical consideration.…”