Doxazosin withdrawal and ambulatory blood pressure monitoring in normotensive subjects

Add-on therapy with a nighttime dose of doxazosin in patients with uncontrolled hypertension: effects on autonomic modulation of the cardiovascular system

This study was designed to determine whether or not the addition of a single nighttime dose of doxazosin in extended-release form (GITS; gastrointestinal therapeutic system) would affect the autonomic modulation of the cardiovascular system in patients with uncontrolled hypertension treated with a multi-drug regimen. Resting 5-min noninvasive finger blood pressure and ECG signals, as well as 24-h Holter ECGs, were recorded in 30 patients with uncontrolled hypertension on multi-drug treatment before and after 16-week add-on therapy with doxazosin GITS. Cardiovascular autonomic modulation was evaluated by spectral analysis of heart rate variability (HRV) and a cross-correlation method for spontaneous baroreflex sensitivity (BRS) in 5-min resting recordings, and by the analysis of Poincaré plots and phase-rectified signal averaging of the duration of cardiac cycles in 24-h ECG recordings. This combined therapy significantly reduced systolic pressure (19.4+/-3.5 mmHg; p<0.0001), diastolic blood pressure (9.4+/-2.0 mmHg; p=0.0003), and pulse pressure (10.0+/-2.8 mmHg; p=0.0021). Concomitantly, there was a significant increase in resting spontaneous BRS (p=0.0191) and increases in 24-h short-term (p=0.0129) and total (p=0.0153) HRV, but with no significant change in heart rate or other measures of HRV. The improvements in HRV and BRS were observed mainly in patients already treated with thiazide diuretics. There was a significant association (r=0.49; p=0.0065) between the degree of change in diastolic blood pressure and short-term HRV caused by the combined treatment. The addition of 4 mg doxazosin GITS to multi-drug antihypertensive therapy is associated with an improvement in cardiovascular autonomic control.

A Review of the Adverse Effects of Peripheral Alpha-1 Antagonists in Hypertension Therapy

BACKGROUND: Doxazosin and its role as an antihypertensive agent have come under recent scrutiny as a result of the early termination of that treatment arm in ALLHAT. It is unclear why the cardiovascular (CV) event rate in this randomized, controlled trial (RCT), especially heart failure, is higher in those treated with a doxazosin-based regimen than with a chlorthalidone based-regimen. There has been little work in the past to summarize information on peripheral alpha-1 antagonists that may be helpful in evaluating the results of this randomized controlled trial. METHODS: Using Medline and the Cochrane databases, we performed a comprehensive review of the literature on the use of peripheral alpha-1 antagonists as antihypertensive agents, focusing on available information that could explain the excess cardiovascular events observed in the Antihypertensive and Lipid-Lowering Treatment to prevent Heart Attack Trial (ALLHAT). RESULTS: Minimal data were available concerning the effects of peripheral alpha-1 antagonists on CV endpoints. A multitude of short-term studies-ranging from small observational studies to short-term moderate-sized RCTs - focused on safety, efficacy, and tolerability, and some studies investigated the physiologic effects of these agents. These previously reported studies reveal associations with weight gain, fluid retention, and neurohormonal changes among various populations of those treated with peripheral alpha-1 antagonists. CONCLUSION: These findings suggest several possible mechanisms by which doxazosin may be inferior to low-dose diuretics as antihypertensive therapy for the prevention of heart failure.

Effect of administration and withdrawal of doxazosin on ambulatory blood pressure in patients with essential hypertension

The effect of both administration and withdrawal of doxazosin on patients with essential hypertension was evaluated by twenty-four-hour ambulatory blood pressure (BP) monitoring. Six hypertensive men were treated with doxazosin starting at 1 mg/day, and the dosage was titrated at weekly intervals up to a maximum of 8 mg/day. The twenty-four-hour BP profile was monitored noninvasively before treatment, in the fourth week of treatment, and on days 2 and 7 after the discontinuation of doxazosin. The average twenty-four-hour systolic and diastolic BPs (SBP and DBP) were lowered by doxazosin treatment and returned to the pretreatment levels within two days of doxazosin withdrawal. Doxazosin treatment produced a significant decrease in the daytime SBP and DBP but not in the nighttime BP values. The daytime BP decrease was no longer detected on days 2 and 7 after drug withdrawal. The twenty-four-hour pulse rate was not influenced by either doxazosin administration or discontinuation. The plasma norepinephrine concentration and plasma renin activity were increased by doxazosin treatment and were decreased by drug withdrawal. There was no rebound hypertension following doxazosin withdrawal. Thus, the present study using twenty-four-hour BP monitoring showed that doxazosin treatment reduced the daytime BP in patients with essential hypertension and that this reduction was abolished within two days after doxazosin discontinuation.