24-hour control of blood pressure by once daily doxazosin: a multicentre double-blind comparison with placebo

Blood pressure lowering efficacy of alpha blockers for primary hypertension

BACKGROUND

Alpha blockers are occasionally prescribed for hypertension so it is important to determine and compare their effects on blood pressure (BP), heart rate and withdrawals due to adverse effects (WDAE).

OBJECTIVES

To quantify the dose-related systolic and/or diastolic BP lowering efficacy of alpha blockers versus placebo in the treatment of primary hypertension.

SEARCH METHODS

For the updated review, we searched CENTRAL (The Cochrane Library 2012, Issue 4), MEDLINE (1946 to May 2012), EMBASE (1980 to May 2012) and reference lists of articles.

SELECTION CRITERIA

Double-blind, randomized, controlled trials evaluating the BP lowering efficacy of fixed-dose monotherapy with an alpha blocker compared with placebo for a duration of 3 to 12 weeks in patients with primary hypertension.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed the risk of bias and extracted data. Study authors were contacted for additional information. WDAE information was collected from the trials.

MAIN RESULTS

Only 10 trials evaluated the dose-related trough BP lowering efficacy of 4 different alpha blockers in 1175 participants with a baseline BP of 155/101 mm Hg. The data do not suggest that any one alpha blocker is better or worse at lowering BP. The best but unsatisfactory estimate of the trough BP lowering efficacy for alpha blockers is -8/-5 mmHg.

AUTHORS' CONCLUSIONS

Based on the limited number of published RCTs, the BP lowering effect of alpha blockers is modest; the estimate of the magnitude of trough BP lowering of -8/-5 mmHg is likely an overestimate. There are no clinically meaningful BP lowering differences between different alpha blockers. The review did not provide a good estimate of the incidence of harms associated with alpha blockers because of the short duration of the trials and the lack of reporting of adverse effects in many of the trials.

Blood pressure lowering efficacy of alpha blockers for primary hypertension

BACKGROUND

Alpha blockers are occasionally prescribed for hypertension so it is important to determine and compare their effects on blood pressure (BP), heart rate and withdrawals due to adverse effects (WDAE).

OBJECTIVES

To quantify the dose-related systolic and/or diastolic BP lowering efficacy of alpha blockers versus placebo in the treatment of primary hypertension.

SEARCH STRATEGY

We searched CENTRAL (The Cochrane Library 2009, Issue 1), MEDLINE (1950 to April 2009), EMBASE (1980 to April 2009) and reference lists of articles.

SELECTION CRITERIA

Double-blind, randomized, controlled trials evaluating the BP lowering efficacy of fixed-dose monotherapy with an alpha blocker compared with placebo for a duration of 3 to 12 weeks in patients with primary hypertension.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed the risk of bias and extracted data. Study authors were contacted for additional information. WDAE information was collected from the trials.

MAIN RESULTS

Only 10 trials evaluated the dose-related trough BP lowering efficacy of 4 different alpha blockers in 1175 participants with a baseline BP of 155/101 mm Hg. The data do not suggest that any one alpha blocker is better or worse at lowering BP. The best but unsatisfactory estimate of the trough BP lowering efficacy for alpha blockers is -8/-5 mmHg.

AUTHORS' CONCLUSIONS

Based on the limited number of published RCTs, the BP lowering effect of alpha blockers is modest; the estimate of the magnitude of trough BP lowering of -8/-5 mmHg is likely an overestimate. There are no clinically meaningful BP lowering differences between different alpha blockers. The review did not provide a good estimate of the incidence of harms associated with alpha blockers because of the short duration of the trials and the lack of reporting of adverse effects in many of the trials.

Efficacy and tolerability of doxazosin versus enalapril in the treatment of patients with mild-to-moderate hypertension

The effects of 4 weeks of treatment with doxazosin or enalapril on diastolic blood pressure (DBP) and plasma lipid levels were studied in 160 patients 18 to 50 years old with mild-to-moderate hypertension. Comparing baseline measurements with measurements taken after 4 weeks, DBP was significantly reduced by 6.8 +/- 7.4 (mean +/- SD) mm Hg and 12.0 +/- 7.1 mm Hg in the doxazosin and enalapril groups, respectively. Systolic blood pressure was significantly decreased from baseline to end of treatment in both groups. There were no significant changes in heart rate from baseline to end of treatment in the doxazosin group, but there was a statistically significant decrease in heart rate in the enalapril group. High-density lipoprotein cholesterol increased statistically significantly in the doxazosin group but not in the enalapril group. A decrease in triglycerides was statistically significant with respect to the doxazosin group and was close to significance for the enalapril group. Forty-nine (62%) patients in the doxazosin group and 43 (54%) patients in the enalapril group reported at least one adverse event. Significant reductions in DBP after 4 weeks of treatment were achieved by both drugs, each taken once daily. This reduction was more pronounced in the enalapril group 24 hours postdose, with a mean final daily dose of 2.8 mg of doxazosin and 12.6 mg of enalapril. However, even relatively short-term treatment with low-dose doxazosin showed a more favorable effect on lipids than did enalapril.

Chronopharmacologic considerations when treating the patient with hypertension: a review

Recognition of the existence of circadian variation in exacerbation of cardiovascular disease may have relevance to clinical use of cardioactive agents. Physiologic rational for the chronobiology of cardiac disease exists and can provide a basis on which to examine the efficacy of agents to manage cardiac disease. The use of 24-hour ambulatory blood pressure monitoring (ABPM) devices have advanced our ability to describe the interplay of chronobiologic rhythms and pharmacodynamic response to antihypertensive medications. This review summarizes the studies evaluating the use of various antihypertensive medications in the context of using 24-hour blood pressure monitoring devices. The studies are described in an attempt to increase awareness of chronobiology and potential implications of designing chronotherapeutic regimens.

Comparative and combined efficacy of doxazosin and enalapril in hypertensive patients

Twenty patients with essential hypertension were randomised to a 7-week period of dose titration with doxazosin, 1-8mg/day or enalapril, 5-20mg/day. In a further 7-week period the dosage level reached with the initial drug was halved, and titration with the second agent was carried out. Blood pressure responses at the end of each treatment period were assessed by clinic measurements made 24 hours post-dose. In the first treatment period, enalapril (mean dose 19mg/day) reduced serum free ACE activity by 40% and had a greater effect than doxazosin (mean dose 5.2mg/day) on clinic supine blood pressure (systolic and diastolic). In the second period, the addition of enalapril to doxazosin was associated with a significant fall in clinic standing blood pressure (systolic and diastolic), despite the doxazosin dose reduction and consequent decrease in median plasma doxazosin concentration (from 10.6 to 5.2ng/ml). Alternatively, when doxazosin was added to enalapril, free ACE activity remained 40% decreased despite enalapril dose reduction, and blood pressure was not further affected. Plasma renin activity was increased by enalapril. No changes were observed in plasma aldosterone or lipid concentrations with either drug. The combination of doxazosin and enalapril was well tolerated and lowered blood pressure overall. Judged by clinic measurements 24 hours post-dose, most of the antihypertensive effect was attributable to the enalapril component. However, ambulatory blood pressure monitoring 0-12 hours post-dose in a subset of patients suggested a contribution of doxazosin earlier in the dose interval.

Selective alpha 1-adrenoreceptor blockers in the treatment of hypertension: should we be using them more?

It has become apparent in recent years that in the treatment of essential hypertension, reduction of blood pressure alone is not sufficient to reduce significantly the morbidity and mortality from ischaemic heart disease. Since the emergence of a multifactorial approach to the prevention of cardiovascular disease, the potential interaction between antihypertensive therapy and metabolic factors, such as control of blood glucose and lipid levels, has become an important consideration. Abnormal function of the sympathetic nervous system may contribute to both the initiation, or maintenance, of hypertension and the associated metabolic disturbances. The new generation of selective alpha 1-adrenoreceptor blockers, besides lowering blood pressure, appear to have favourable effects on lipid and glucose metabolism. The use of these drugs and their place in the treatment of hypertension are discussed.

Doxazosin: a study in a cohort of patients with hypertension in general practice--an interim report

The objective of this study was to assess the safety and efficacy of doxazosin in a substantial cohort of hypertensive patients drawn from general practice. A total of 4027 patients entered the study, 1472 of whom (36.6%) were untreated hypertensive patients. Patients were not advised to change diet, smoking habit, or life-style during the study. Twenty-one percent were cigarette smokers, and concurrent diabetes was present in 2.3%. Baseline blood cholesterol exceeded 200 mg/dl (5.2 mmol/L) in 90% and 250 mg/dl (6.5 mmol/L) in 56% of patients. The mean decrease in blood pressure produced by doxazosin was 22/15 mm Hg after 10 weeks of therapy; there was a mean decrease in heart rate of 1 beat/min. The mean maintenance dose for all patients was 3.1 mg/day. Side effects considered related or possibly related to treatment were reported in 705 patients. Treatment was discontinued in 233 patients (5.8%) because of adverse events related or possibly related to treatment with doxazosin. Doxazosin produced a significant (p less than 0.001) decrease in total cholesterol, low-density lipoprotein cholesterol, and triglyceride levels and a significant increase in high-density lipoprotein cholesterol and the ratio of high-density lipoprotein:total cholesterol. The potential reduction in 10-year coronary heart disease risk (according to the Framingham equation) was calculated to be 20.4%.

Alpha-adrenergic blockers: mechanism of action, blood pressure control, and effects of lipoprotein metabolism

The sympathetic nervous system plays a major role in the pathogenesis of essential hypertension and is mediated by the alpha and beta receptors. The alpha receptor is divided into two types, alpha 1 and alpha 2, based on response to epinephrine and norepinephrine. alpha 1-Adrenergic receptors have a high affinity for drugs such as prazosin, doxazosin, and terazosin, which act to reduce blood pressure by selective blockade of the receptor. These agents provide a rational approach to the treatment of hypertension by correcting elevated total peripheral resistance, the fundamental hemodynamic abnormality in essential hypertension. In contrast, early alpha-adrenergic receptor blockers nonselectively blocked both alpha 1 and alpha 2 receptors and were unsuitable as antihypertensive agents because they induced tachycardia and patients developed a tolerance to them rapidly. alpha 1-Adrenergic blockers also have beneficial effects on plasma lipoproteins, tending to decrease levels of triglycerides and cholesterol and increase levels of high-density lipoprotein (HDL) cholesterol and the HDL cholesterol/total cholesterol ratio. beta-Adrenergic blockers, such as propranolol and atenolol, have been shown to have an adverse effect on the lipid profile by tending to increase levels of triglycerides and decrease HDL cholesterol. A number of mechanisms contribute to these effects, in particular, adrenergic modulation of lipoprotein lipase and the triglyceride secretion rate. Doxazosin has been shown to increase the activity of LDL receptors, which may be partly responsible for its beneficial effect on plasma lipids and lipoproteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical pharmacotherapeutics of doxazosin

Doxazosin is the latest in a series of highly selective postsynaptic alpha 1-adrenoceptor inhibitors. It is readily absorbed, with high bioavailability and a relatively long plasma half-life, neither of which property is influenced by age. This accounts for the prolonged pharmacologic activity of doxazosin following a single oral dose. Its prime pharmacodynamic activity resides in its ability to counter sympathetic vasoconstriction of the systemic arteriolar resistance vessels and venous capacitance system, which enables the drug to target the major pathophysiologic abnormality in hypertension, i.e., the generalized systemic arteriolar constriction. The widespread vasodilation induced by doxazosin relieves both cardiac preload and afterload and, consequently, reduces left ventricular wall stress and myocardial oxygen consumption. In hypertension, doxazosin reduces blood pressure both at rest and during exercise by reduction of systemic vascular resistance without precipitating substantial reflex cardiac stimulation. The effects are maximal on the standing blood pressure between two and four hours after ingestion; due to doxazosin's relatively slow absorption, postural hypotension is infrequent. Its antihypertensive activity is maintained over 24 hours following a single oral dose, and the optimal dose range is 2 to 8 mg once daily. The antihypertensive efficacy of doxazosin has been shown to be comparable with that of other alpha-adrenoceptor inhibitors, beta-blocking drugs, diuretics, calcium antagonists, and angiotensin-converting enzyme inhibitors. In contrast to other conventional antihypertensive drugs, a unique feature of alpha-adrenoceptor-inhibiting drugs, including doxazosin, is their ability to reduce the plasma concentrations of triglycerides, total cholesterol, and low-density lipoprotein cholesterol and to increase high-density lipoprotein cholesterol concentration. This contrasts with the opposite effect on lipid levels induced by hydrochlorothiazide and atenolol seen in comparative studies. Side effects show no predilection for any organ system, and the overall incidence of such effects compares well with those of other commonly used antihypertensive drugs. This unique combination of antihypertensive efficacy and favorable effect on blood lipid levels indicates that once-daily treatment with doxazosin holds considerable promise in the treatment of hypertension, both from the point of view of its antihypertensive efficacy and also from its primary preventative potential.

Pharmacotherapeutic stature of doxazosin and its role in coronary risk reduction

In hypertension the primary pathophysiologic abnormality is a generalized increase in the peripheral vascular resistance as a result of concentric narrowing of the systemic arterioles, as a result of alpha 1-receptor stimulation. Such stimulation is attenuated by the selective alpha 1-inhibitor doxazosin. The pharmacologic attributes of doxazosin are translated into direct relaxation of the peripheral arteriolar resistance vessels and venous capacitance system, particularly those with a high alpha-adrenoceptor population. The direct effects of such vascular dilatation are immediately beneficial to the heart in reducing systemic and pulmonary vascular pressures that reduce left ventricular wall stress and myocardial oxygen consumption. In clinical studies doxazosin has been found to have a plasma half-life of 19 to 22 hours, of which a single daily dose is sufficient to control hypertension. The antiatherogenic changes in the blood lipid profile resulting from long-term treatment with doxazosin can also be expected to advance its primary prevention potential in hypertensive patients, which is in marked contrast to the potentially disadvantageous changes in the blood lipid profile that follow treatment with beta-blockers and thiazide diuretics. The therapeutic efficacy of doxazosin has been confirmed, irrespective of hypertension severity, age and race of the patient, or the presence of renal impairment or diabetes mellitus. Its side-effect profile is not substantially different from that of placebo or other antihypertensive drug treatment. Given its unique actions regarding antihypertensive efficacy, together with favorable effects on blood lipids, doxazosin probably holds more promise for the prevention of precocious coronary heart disease in hypertensive patients than any other currently available antihypertensive agent.