A comparison of the effects of labetalol, bendrofluazide and their combination in hypertension

Effect of diuretics on plasma renin activity in primary hypertension: A systematic review and meta-analysis

AIMS

Plasma renin activity (PRA) is regarded as a marker of sodium and fluid homeostasis in patients with primary hypertension. Whether effects of diuretics on PRA differ according to class of diuretic, whether diuretics lead to a sustained increase in PRA, and whether changes in PRA relate to those in blood pressure (BP) is unknown. We performed a systematic review and meta-analysis of trials investigating the antihypertensive effects of diuretic therapy in which PRA and/or other biomarkers of fluid homeostasis were measured before and after treatment.

METHODS

Three databases were searched: MEDLINE, EMBASE and The Cochrane Central Register of Controlled Trials. Titles were firstly screened by title and abstract for relevancy before full-text articles were assessed for eligibility according to a predefined inclusion/exclusion criteria.

RESULTS

A total of 1684 articles were retrieved of which 61 met the prespecified inclusion/exclusion criteria. PRA was measured in 30/61 studies. Diuretics led to a sustained increase in PRA which was similar for different classes of diuretic (standardised mean difference [95% confidence interval] 0.481 [0.362, 0.601], 0.729 [0.181, 1.28], 0.541 [0.253, 0.830] and 0.548 [0.159, 0.937] for thiazide, loop, mineralocorticoid receptor antagonists/potassium-sparing and combination diuretics respectively, Q = 0.897, P = .826), and did not relate to the average decrease in blood pressure.

CONCLUSION

In antihypertensive drug trials, diuretics lead to a sustained increase in average PRA, which is similar across different classes of diuretic and unrelated to the average reduction in blood pressure.

Labetalol (Trandate, Glaxo Inc.; Normodyne, Schering Corp.)

Labetalol is a competitive antagonist of α1-, β1-, and β2-adrenergic receptors. The hemodynamic effects of the drug include reduced blood pressure, heart rate, and peripheral resistance, with little change in resting cardiac output or stroke volume. In open trials and controlled studies, labetalol was an effective antihypertensive. Labetalol compared favorably with β-blockers alone or in combination with vasodilators, for the treatment of hypertension. Reductions in heart rate are less pronounced with labetalol as compared with propranolol. Labetalol produces rapid reductions in blood pressure when administered intravenously for severe hypertension. The most frequent adverse reactions to the drug include fatigue, postural symptoms, headache, and gastrointestinal complaints. Labetalol may prove advantageous when vasodilation in addition to β-blockade is desired, or for selected patients experiencing adverse effects attributable to β-blockade. Until the clinical profile of labetalol is better defined, the use of the drug should be limited.

Properties of labetalol, a combined alpha- and beta-blocking agent, relevant to the treatment of myocardial ischemia

Labetalol, a combined alpha-beta-adrenergic antagonist, is one of the new group of beta-adrenergic blockers reduces peripheral and coronary vascular resistances while preserving cardiac output. Unlike alpha-adrenergic blockers, labetalol tends to reduce heart rate during rest and exercise. The drug is a potent antihypertensive agent which has been used by mouth and by vein to treat mild, moderate, and severe hypertension, including hypertensive emergencies. Labetalol has a hemodynamic profile which makes it an attractive agent for treating myocardial ischemia. The drug reduces blood pressure, left ventricular wall tension, heart rate, and contractility while preserving or even augmenting coronary blood flow. Studies with labetalol in hypertensive patients with angina have shown it to be more effective than placebo in reducing angina attacks and blood pressure while improving exercise tolerance. The drug appears to have antianginal and antihypertensive effects comparable to atenolol and propranolol. Side effects of treatment are observed and most are related to alpha- and beta-adrenergic blockade. Labetalol also appears to be effective for treatment of normotensive patients with angina and for silent myocardial ischemia. It has no apparent effects on serum lipids and lipoproteins. Labetalol appears to be a useful drug for treating the hypertensive heart and its many complications.

Labetalol in the treatment of essential hypertension: a single-blind dose ranging study

The hypotensive efficacy of labetalol was evaluated in 29 patients with essential hypertension in a single-blind dose ranging study. After a two-week period of placebo treatment, labetalol was given in oral doses of 0.6 g/d, 0.8 g/d, and 0.8 g/d combined with 25-50 mg/d of hydrochlorothiazide. Each regimen lasted four weeks. The decrease in blood pressure was dose dependent: 90% of patients showed a significant reduction in diastolic blood pressure and 75% showed a significant reduction in systolic blood pressure. In 69% of the patients, side effects of the drug were noted, and in five patients (17%), treatment was discontinued because of the side effects. Seven patients received labetalol intravenously before the oral treatment. Their heart rate and blood pressure reductions were similar to those found in patients only taking the medication orally. We conclude that labetalol is an efficient and safe antihypertensive agent in both oral and intravenous administration. However, the high incidence of side effects makes labetalol a drug of second choice in uncomplicated hypertensive patients.

Alternative pharmacologic approaches to the initial management of hypertension

Recent clinical trials in hypertension report more deaths due to coronary heart disease in mild hypertensives who received aggressive antihypertensive drug therapy and achieved better blood pressure control. Subset analyses of these trials suggest that diuretic therapy may have contributed to this outcome, possibly through a reduction in serum potassium or an elevation in serum lipids. Because of this, patients with an abnormal pretreatment electrocardiogram, history of myocardial infarction, unstable coronary heart disease, or diuretic-induced hyperlipidemia or hypokalemia unresponsive to management are candidates for alternative antihypertensive agents. A review of the literature suggests that most of the currently available beta-blockers, the alpha 1-antagonist prazosin, the angiotensin-converting enzyme inhibitor captopril, and the vasodilator hydralazine are effective alternatives to thiazide therapy in the initial management of hypertension and are recommended for particular subgroups of patients. Monotherapy with the centrally and peripherally acting sympatholytic agents is not recommended because of the frequent side effects encountered and the inferior hypotensive efficacy reported. Calcium channel blocking agents also appear to be suitable alternatives to thiazides in hypertension, but more experience with these is needed. Alternative pharmacologic agents may be selected on the basis of age, and, to a lesser extent, race.

A comparison of labetalol and prazosin combined with atenolol in non-responders to atenolol plus hydrochlorothiazide in uncomplicated hypertension

After screening two local populations in the northern part of The Netherlands for hypertension, patients with a diastolic pressure (DP) between 95 and 120 mmHg were treated daily either with 50 mg hydrochlorothiazide or 100 mg atenolol. Nonresponders were given the combination and if necessary the dose of atenolol was increased to 200 mg. Non-responders to the latter combination were randomized and treated either with 50 mg hydrochlorothiazide and labetalol or with 50 mg hydrochlorothiazide, 200 mg atenolol and prazosin. If after 1 month a DP less than or equal to 90 mmHg had been reached the patient was reassessed after a further 3 months. If a DP greater than 90 mmHg was found the dose of labetalol or prazosin was increased and the patient was re-examined after 1 month. This protocol was followed until the maximum dose was reached or adverse reactions prevented a further increase in dosage. During 6 months of treatment there was a further drop in systolic and diastolic blood pressures under both regimens of, respectively, 8.6 and 2.4 mmHg for labetalol, and 7.7 and 5.0 mmHg for the prazosin group. At the end of the period the average daily doses of labetalol and prazosin were 1256 mg and 4.3 mg, respectively. There was no significant difference in the average number of complaints between the labetalol and the prazosin group.

Effect of indoramin, labetalol and alinidine on sympathetic function in normal man

The effects of single oral doses of indoramin (mean dose 58 mg), abetalol (mean dose 150 mg), alinidine 80 mg and placebo on arterial pressure and heart rate in the supine and standing positions were studied in six normal volunteers. Doses were chosen to give equivalent reductions of arterial pressure in the standing position. Observations were made before and at 2 and 4 h after drug administration. Plasma noradrenaline (NA) was measured at each time interval in the supine position, and after 4 min of standing. Plasma renin activity (PRA) was measured at each time interval after 30 min in the standing position. In the supine position, alinidine produced a significant reduction of systolic arterial pressure from 124.0 +/- 3.0 mm Hg to 104.3 +/- 4.1 mm Hg at 2 h (P less than 0.01) and to 101.7 +/- 2.2 mm Hg at 4 h (P less than 0.01). Diastolic pressure was reduced from 74.7 +/- 2.6 mm Hg to 57.0 +/- 4.6 mm Hg at 4 h (P less than 0.01). Arterial pressure was unchanged after indoramin or labetalol administration. In the supine position, heart rate was unchanged after indoramin, and small reductions were observed after labetalol and alinidine. Indoramin produced a significant increase in plasma NA. A small increase of plasma NA was observed after labetalol, and a small decrease after alinidine. In the standing position, the three active drugs reduced systolic arterial pressure to a similar extent (indoramin, -26.7 mm Hg at 4 h after drug administration; labetalol, -21.3 mm Hg at 2 h; alinidine, -21.7 mm Hg at 4 h).(ABSTRACT TRUNCATED AT 250 WORDS)

Combined alpha- and beta-receptor inhibition in the treatment of hypertension

Both beta- and alpha-adrenergic mechanisms are important in the control of blood pressure; alpha-mediated vasoconstriction is responsible for the regulation of vascular tone, and beta-mediated responses stimulate the heart directly and indirectly by liberating renin and affecting vascular smooth muscle tone. beta-Adrenergic blocking drugs have long been established in the treatment of hypertension. The development of drugs which combine this action with an alpha-blocking effect represents an additional mode of action to lower the blood pressure. Numerous studies have demonstrated that labetalol intravenously or orally gives a rapid fall of blood pressure in essential and renal hypertension. It has also been used intravenously in phaeochromocytoma, tetanus, clonidine withdrawal, and as an adjunct to halothane to produce hypotensive anaesthesia. Intravenously, labetalol is probably best given as a graded infusion or as repeated small bolus injections to assure a smooth fall of blood pressure. Many long term studies have shown it to be effective orally in prolonged treatment of hypertension with studies of over 5 years, showing that tolerance does not develop. Labetalol can be used in combination with diuretics and other drugs when necessary. It can be employed to control the blood pressure in all grades of hypertension. A dosage of 100mg twice daily will often be adequate to control mild hypertension and the use of even lower doses has been reported. However, the dosage can be markedly increased in severe hypertension and while such doses are relatively exceptional, several trials have employed over 2 g per day for the more resistant cases. Studies have demonstrated that blood pressure control with labetalol is equivalent to that with beta-adrenoceptor blocking drugs plus vasodilators, or methyldopa. Labetalol has been used in patients with severe renal impairment and a number of studies suggest that it may now be the drug of choice in raised blood pressure of pregnancy. Side effects can be divided into those related to beta-blockade, those related to alpha-blockade and those not clearly related to either effect. It has been suggested that the side effects attributable to the beta-blocking component are less obtrusive than those seen with pure beta-blocking drugs without alpha-activity because the alpha-blockade modifies the consequences of beta-blockade. Heart failure has been reported, but for haemodynamic reasons would be expected to be less common; careful patient selection should avoid any risk. Similarly labetalol may worsen asthma even if the risks are probably less than with non-selective beta-blockade alone.(ABSTRACT TRUNCATED AT 400 WORDS)

Labetalol: a review of its pharmacology, pharmacokinetics, clinical uses and adverse effects

Labetalol is a combined alpha- and beta-adrenoceptor blocking agent for oral and intravenous use in the treatment of hypertension. It is a nonselective antagonist at beta-adrenoceptors and a competitive antagonist of postsynaptic alpha 1-adrenoceptors. Labetalol is more potent at beta that at alpha 1 adrenoceptors in man; the ratio of beta-alpha antagonism is 3:1 after oral and 6.9:1 after intravenous administration. Labetalol is readily absorbed in man after oral administration, but the drug, which is lipid soluble, undergoes considerable hepatic first-pass metabolism and has an absolute bioavailability of approximately 25%. There are no active metabolites, and the elimination half-life of the drug is approximately 6 hours. Unlike conventional beta-adrenoceptor blocking drugs without intrinsic sympathomimetic activity, labetalol, when given acutely, produces a decrease in peripheral vascular resistance and blood pressure with little alteration in heart rate or cardiac output. However, like conventional beta-blockers, labetalol may influence the renin-angiotensin-aldosterone system and respiratory function. Clinical studies have shown that the antihypertensive efficacy of labetalol is superior to placebo and to diuretic therapy and is at least comparable to that of conventional beta-blockers, methyldopa, clonidine and various adrenergic neuronal blockers. Labetalol administered alone or with a diuretic is often effective when other antihypertensive regimens have failed. Studies have shown that labetalol is effective in the treatment of essential hypertension, renal hypertension, pheochromocytoma, pregnancy hypertension and hypertensive emergencies. In addition, preliminary studies indicate that labetalol may be of value in the management of ischemic heart disease. The most troublesome side effect of labetalol therapy is posture-related dizziness. Other reported side effects of the drug include gastrointestinal disturbances, tiredness, headache, scalp tingling, skin rashes, urinary retention and impotence. Side effects related to the beta-adrenoceptor blocking effect of labetalol, including asthma, heart failure and Raynaud's phenomenon, have been reported in rare instances.

Comparison of labetalol, propranolol and hydralazine in hypertensive out-patients

In a randomized cross-over trial the combination labetalol/hydrochlorothiazide was compared with the combination of propranolol/hydralazine/hydrochlorothiazide in 34 uncomplicated hypertensive patients, who were not satisfactorily controlled with hydrochlorothiazide 50 mg alone. The elevated diastolic pressure (D.P.) in 27 patients responded satisfactorily to the labetalol schedule and in 28 patients to the propranolol/hydralazine schedule. No difference was found in the rate of decrease of D.P., nor in the disappearance of hypertension-related complaints. Although the duration of the washout between treatments was at least one month, treatment was significantly more efficacious during the second period. Labetalol pre-treatment especially seemed to enhance the effect of subsequent propranolol/hydralazine administration. Side effects due to therapy were rare and were not related to any particular treatment. The median daily dose of labetalol in responders was 600 mg and that of propranolol/hydralazine 120/60 mg (in both therapies hydrochlorothiazide 50 mg was given in addition). Patients showed a slight preference for the labetalol medication. It is concluded that labetalol/hydrochlorothiazide and propranolol/hydralazine/hydrochlorothiazide are equally satisfactory in the treatment of uncomplicated hypertension.

Comparison of labetalol with other anti-hypertensive drugs

1 The anti-hypertensive effects of labetalol have been compared and contrasted with other groups of anti-hypertensive drugs in this review of the published literature. 2 The data show that the pharmacological and haemodynamic profile of labetalol in man is distinctly different from that of other specific anti-hypertensive agents; namely the properties of competitive alpha-and beta-adrenoceptor blockade leading to haemodynamic effects of reduced blood pressure and peripheral vascular resistance with little accompanying changes in resting heart rate or cardiac output. 3 The anti-hypertensive effects of labetalol are dose related. In fixed dose comparative studies equivalent anti-hypertensive effects to those of labetalol have been shown for individual drugs of the beta-adrenoceptor-blocking and diuretic groups. In dose titration studies, equivalent anti-hypertensive effects at given doses of labetalol have been demonstrated for drugs of the following types: beta-adrenoceptor blockers, beta-blockers plus diuretics, methyldopa, adrenergic neurone blockers and the combination of beta-blockers plus a peripheral vasodilator. 4 Comparing side-effect liabilities, it is clear that quantitatively labetalol produces no greater burden of side-effects than drugs of the beta-adrenoceptor-blocking group. Qualitative differences, however, do exist; in particular, symptomatic postural hypotension is dose related and is more likely to occur when excessive doses (greater than 2 g daily) are used.

Pharmacokinetics of bendroflumethiazide alone and in combination with propranolol and hydralazine

Bendroflumethiazide (Bft) was administered to 6 healthy subjects at 3 different dose levels (2.5, 5 and 10mg) in a cross-over design, either as capsules (2.5mg) or as tablets (5mg). Its pharmacokinetics were evaluated then and following administration of a fixed combination of Bft and propranolol and hydralazine to a further 7 volunteers. Plasma and urinary concentrations of Bft were determined by a new fluorimetric - thin-layer chromatography procedure. Peak plasma levels occurred after 2-3h and averaged 15, 27 and 45 microgram/l in the three dose groups. Areas under the plasma concentration - time curves (AUC0 leads to 12), which were 75, 147 and 250 microgram 1(-1)h respectively, and cumulative urinary recovery (20%) were independent of the dose administered and the type of formulation. Thus Bft kinetics proved to be linear within the dose range evaluated. The plasma clearance was calculated to be 505 ml/min, renal clearance 108 ml/min and nonrenal clearance 396 ml/min. Bioavailability of Bft was not altered following administration of the fixed combination. The amount of propranolol found in the circulation did not change, whereas that of hydralazine (determined as apparent hydralazine) increased by 59% when the fixed combination was administered.

Blood pressure, body fluid volumes and glomerular filtration rate during treatment with labetalol in essential hypertension

1 In a single blind study seventeen patients with mild or moderate essential hypertension and normal renal function were treated with labetalol alone in increasing doses from 300 via 600 to 1200 mg daily. 2 Average supine BP (systolic/diastolic) was reduced by 24/19 mm Hg. Seven patients attained a diastolic BP less than or equal to Hg. A significant postural fall in systolic BP was recorded, but no symptomatic orthostatic hypotension occurred. 3 In twelve patients measurements of plasma volume (125I-albumin), extracellular volume (82Br-space) and glomerular filtration rate (51Cr-EDTA clearance) on placebo and subsequently labetalol showed no systemic changes. 4 Side effects were few causing two withdrawals because of impotence and arthralgia. 5 It is concluded that monotherapy with labetalol results in clinically relevant, persistent and dose dependent reduction in BP in patients with mild or moderate essential hypertension, apparently without concomitant expansion of body fluid volumes or influence on glomerular filtration rate.