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

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.

How Do Antihypertensive Drugs Work? Insights from Studies of the Renal Regulation of Arterial Blood Pressure

Though antihypertensive drugs have been in use for many decades, the mechanisms by which they act chronically to reduce blood pressure remain unclear. Over long periods, mean arterial blood pressure must match the perfusion pressure necessary for the kidney to achieve its role in eliminating the daily intake of salt and water. It follows that the kidney is the most likely target for the action of most effective antihypertensive agents used chronically in clinical practice today. Here we review the long-term renal actions of antihypertensive agents in human studies and find three different mechanisms of action for the drugs investigated. (i) Selective vasodilatation of the renal afferent arteriole (prazosin, indoramin, clonidine, moxonidine, α-methyldopa, some Ca(++)-channel blockers, angiotensin-receptor blockers, atenolol, metoprolol, bisoprolol, labetolol, hydrochlorothiazide, and furosemide). (ii) Inhibition of tubular solute reabsorption (propranolol, nadolol, oxprenolol, and indapamide). (iii) A combination of these first two mechanisms (amlodipine, nifedipine and ACE-inhibitors). These findings provide insights into the actions of antihypertensive drugs, and challenge misconceptions about the mechanisms underlying the therapeutic efficacy of many of the agents.

Cardiovascular risk, drugs and erectile function--a systematic analysis

AIMS

Erectile dysfunction is a major problem with an increasing prevalence in cardiovascular high-risk patients due to its association with cardiovascular risk factors. Drugs used for evidence-based treatment of cardiovascular diseases have been reported to decrease erectile function, but possible mechanisms are poorly characterised.

METHODS

MEDLINE, EMBASE and Cochrane Registry search were performed including manuscripts until January 2010. Searching terms are: 'erectile dysfunction or impotence' in combination with 'ACE-inhibitors', 'angiotensin', 'beta-blockers', 'calcium antagonist' and 'diuretics'. Animal studies, letters, reviews, case-reports and manuscripts other than English language and trials dealing with combination treatment are excluded.

RESULTS

Analysis of literature revealed five epidemiological trials evaluating the effect of different cardiovascular drugs on erectile function. There were eight trials evaluating the effect of beta-blockers, five trials evaluating the effect of ace-inhibitors or angiotensin-receptor-blockers and one trial evaluating the effect of diuretics on erectile function. Results of these trials demonstrate that only thiazide diuretics and beta-blockers except nebivolol may adversely influence erectile function. ACE-inhibitors, angiotensin-receptor-blockers and calcium-channel-blockers are reported to have no relevant or even a positive effect on erectile function.

CONCLUSION

Inappropriate patients' concerns about adverse effects of cardiovascular drugs on erectile function might limit the use of important medications in cardiovascular high-risk patients. Knowledge about the effects of drug-treatments on erectile function and about the major role of the endothelium in penile function might improve patients' adherence to evidence based treatment of cardiovascular diseases.

Should β-Blockers Be Used to Control Hypertension in People With Chronic Kidney Disease?

Activation of the sympathetic nervous system is common in patients with chronic kidney disease, plays an important role in the genesis of hypertension, the rate of decrease of renal function, and is associated with the increased cardiovascular morbidity and mortality seen in these patients. beta-blockers are potent antihypertensive agents but differ in their hemodynamic effects on renal function. The cardioselective beta-blockers such as atenolol and metoprolol are known to retard the progression of renal diseases, but to a lesser degree compared with blockers of the renin-angiotensin-aldosterone system. However, the newer vasodilating beta-blockers such as carvedilol and nebivolol have different effects on renal hemodynamics and function primarily because of its greater adjunctive alpha1-blocking activity. Carvedilol decreases renal vascular resistance and prevents reductions in the glomerular filtration rate and renal blood flow in patients with hypertension with or without impaired kidney function. In addition, carvedilol may retard progression of albuminuria, and provide cardiorenal protection in chronic kidney disease patients with hypertension, congestive heart failure, and at high risk for sudden cardiac death.

Beta blockers in the management of chronic kidney disease

The sympathetic nervous system modulates renal function through its receptors namely beta1 (cardiac output and renin release), alpha1 (systemic and renovascular constriction), and beta2 renovascular dilation. Sympathetic overactivity is commonly seen in chronic kidney disease (CKD) and is an important contributor to increasing the risk of cardiovascular events as well as increasing renal disease progression. Recent evaluations of drug use in people with CKD shows a remarkably low percentage of patients receiving beta-blockers, especially in more advanced stage CKD when cardiovascular risk is higher. This is in large part due to tolerability of these agents. Moreover, water-soluble beta-blockers such as atenolol and metoprolol are dialyzable and require supplementation to avoid exacerbation of arrhythmias following dialysis. Newer vasodilating beta-blockers have better tolerability and different effects on renal hemodynamics as well as metabolic variables. These effects are related to the relative alpha1-blocking effect of agents such as carvedilol and labetolol, with carvedilol having relatively greater alpha-blocking effects. Few studies evaluate beta-blockers on cardiovascular risk in CKD patients. Studies with carvedilol demonstrate attenuated increases in albuminuria as well as reduction in cardiovascular events in CKD patients with hypertension. This paper reviews the animal and clinical trial data that evaluate beta-blockers in CKD highlighting the vasodilating beta-blockers. It is apparent that greater use of this drug class for blood pressure control would further enhance reduction of risk of heart failure, the most common cause of death in the first year of starting dialysis.

Clinical experience with dual-acting drugs in hypertension

There are now several antihypertensive agents with dual actions. Among these, labetalol has been studied most extensively. The drug has a place in the chronic treatment of hypertension and in the therapy of hypertensive emergencies. Carvedilol, now available in Germany, has been shown to be effective in different forms of hypertension. Celiprolol binds to beta 1- and beta 2-receptors. This drug also binds to alpha 2-receptors. It is not clear, at present, whether or not this binding property contributes to its antihypertensive effect.

Influence of antihypertensive therapy on renal function

Antihypertensive therapy influences kidney function by different mechanisms depending on the mode of action of the drug used. The GFR is improved by calcium entry blockers and ACE inhibitors, unaffected by vasodilators, alpha-blockers and centrally acting sympatholytics and impaired by beta-blockers. The same is true for renal blood flow and is due to changes of renal vascular resistance. Renal sodium excretion is impaired mostly by vasodilators, by alpha-blockers, sympatholytics and beta-blockers; in contrast, calcium entry blockers and ACE inhibitors acutely induce natriuresis. The RAAS is stimulated by vasodilators, unaffected by alpha-blockers and sympatholytics and suppressed by beta-blockers. Plasma catecholamines are stimulated by vasodilators and suppressed by centrally acting sympatholytics and unaffected by the others. Induction of acute renal functional impairment is reported for ACE inhibitors under conditions of compromised renal perfusion pressure such as in renal artery stenosis. These data from the literature reviewed are supported by our own experimental data on sodium balance under different drugs and micropuncture data in experimental renal artery stenosis. To achieve effective antihypertensive treatment with a low profile of side effects, careful monitoring of renal function seems to be mandatory.

Effects of carvedilol on renal function

A randomized, double-blind, placebo-controlled study was conducted to study the effects of acute and chronic administration of carvedilol in essential hypertension, with special emphasis on renal haemodynamics and function. Acute administration of a single dose of 50 mg carvedilol reduced systolic and diastolic blood pressure without inducing reflex tachycardia. Renal blood flow was preserved; accordingly, renal vascular resistance was significantly reduced. A significant reduction in the glomerular filtration rate and filtration fraction was observed. Plasma renin activity (PRA) and plasma aldosterone values were not changed. Chronic carvedilol treatment produced a significant fall in systolic and diastolic blood pressure, heart rate, PRA and plasma aldosterone. Renal blood flow, glomerular filtration rate and filtration fraction also remained unchanged; renal vascular resistance decreased significantly. It is concluded that carvedilol possesses definite antihypertensive and renal vasodilating properties, both acutely and after chronic treatment.

The renal function and blood pressure effects of dilevalol in the normotensive and hypertensive elderly

Dilevalol, the R-R optical isomer of labetalol, is a nonselective beta adrenergic blocking drug with selective beta-2 agonist properties. In a double-blind, crossover study the renal function effects of dilevalol were compared to placebo in 12 normotensive elderly volunteers before and after single dose administration. In addition, chronic treatment (greater than 4 weeks) effects of dilevalol were determined in eight elderly patients with mild to moderate essential hypertension. Renal function was determined by plasma disappearance curves from single injections of 99mTc-DTPA and 131I-orthohippurate. In both study populations renal function tests commenced two hours after dosing at expected peak plasma levels of dilevalol. Normotensive volunteers had an acute decrease in glomerular filtration rate of 10.3 ml/min, which was significant (P less than 0.05), while hypertensive patients had no change in glomerular filtration rate. There were no significant changes in other parameters of renal function measured. In the hypertensive elderly dilevalol treatment resulted in significant reductions, 18 and 19 mmHg respectively, of systolic (P less than 0.01) and diastolic (P less than 0.001) blood pressure. Heart rate was reduced by 5 beats per minute, and the change was not statistically significant. Dilevalol appears to be an excellent agent for treatment of hypertension in the elderly hypertensive patient, and does not change renal function when administered chronically to the hypertensive patient. Small but significant decrements in glomerular filtration rate occur with acute administration to normotensive volunteers.

Effects of dilevalol on renal function

Renal function was measured in a total of 35 volunteers and patients who were given dilevalol, the R,R optical isomer of labetalol. Young normotensive volunteers (n = 6) and elderly normotensive volunteers (n = 12) received single 400- and 200-mg doses of dilevalol, respectively. Renal function was determined in these subjects on the same day before and after dosing. In addition, patients with mild to moderate essential hypertension (n = 11) and hypertensive patients with renal insufficiency (n = 6) were treated with placebo to establish baseline blood pressure and then were given dilevalol, 400 to 1,600 mg/day, for 2 to 6 weeks until blood pressure was controlled. Renal function was determined at the end of the baseline period and again at the end of dilevalol treatment. A subgroup of elderly hypertensives from the 2 protocols used to study hypertensive patients was treated as a separate study group. The only effect on parameters of renal function seen in any of the study groups was a statistically significant 15% decrease in glomerular filtration rate after single-dose treatment in the elderly normotensive group. Effective renal plasma flow, filtration fraction, renal blood flow and renal vascular resistance were unchanged before and after treatment in all groups. Mean arterial pressure was reduced significantly in all groups except in the elderly normotensive volunteers. Dilevalol appears to be a well-tolerated, effective therapeutic agent that is neutral regarding its effect on renal function and potentially useful in a variety of patient populations.

Effects of dilevalol, an R, R-isomer of labetalol, on blood pressure and renal function in patients with mild-to-moderate essential hypertension

The effects of oral dilevalol (an R, R-isomer of labetalol), a new beta-adrenoceptor blocker with beta 2-receptor stimulating and alpha-recepter blocking properties on blood pressure, renal function, plasma renin activity (PRA) and plasma aldosterone have been studied in 15 patients with mild-to-moderate essential hypertension treated with it for 6 weeks. Two patients with apparent treatment failure and one patient who developed muscle pain and cramps, and had an elevated creatine phosphokinase level, were excluded from the study. Dilevalol monotherapy 100 mg once daily for 6 weeks significantly lowered both the systolic and diastolic blood pressure compared to placebo. Total renal vascular resistance was significantly reduced, and RBF and GFR remained unchanged. Dilevalol significantly decreased PRA. The results suggest that prolonged daily treatment with dilevalol preserves renal function and produces a concomitant hypotensive action in patients with mild-to-moderate essential hypertension. The ancillary pharmacological properties of dilevalol rather than PRA suppression may be relevant to its renal effects.

The combined alpha- and beta-adrenergic blocker labetalol and propranolol in the treatment of high blood pressure: similarities and differences

Labetalol, an agent with both alpha- and beta-adrenoreceptor blocking properties, and the beta blocker propranolol were each given for one month to groups of 15 patients with essential hypertension. With either treatment, 11 of the 15 patients experienced decreased supine diastolic blood pressure to less than 90 mm Hg without evidence of fluid retention. Propranolol significantly increased plasma concentrations of uric acid and potassium, whereas labetalol significantly increased plasma concentration of high-density lipoproteins (HDL) and decreased the total cholesterol:HDL ratio; neither drug significantly changed renal function. During three additional months of labetalol treatment, there was a slight tendency to orthostatic decreases in systolic blood pressure as compared with the values after the initial month. Labetalol had variable effects on plasma renin activity and aldosterone excretion, but within individual patients the values were constant; there were close correlations between changes measured after one month and after four months for both renin (r = 0.86) and aldosterone (r = 0.94). The manifestations of labetalol's alpha-blocking component appeared to be a small postural effect on systolic blood pressure and an increase in plasma HDL.

Propranolol vs metoprolol vs labetalol: a comparative study in essential hypertension

In a double blind, within patient investigation of twenty-four patients (nineteen males and five females) with a mean age of 46.3 years (SD 10.9 years) with mild to moderate essential hypertension a comparison between equipotent beta-blocking doses of propranolol, metoprolol and labetalol was carried out. Blood pressure and pulse rate were measured in lying, sitting and standing positions and before, during and after isometric and dynamic exercise. Peak expiratory flow was recorded before and during dynamic exercise. All the active treatments were better than placebo in reducing blood pressure and heart rate. Comparing the effects of treatment, labetalol lowered sitting diastolic pressure significantly more than propranolol and standing diastolic pressure than both propranolol and metoprolol. Metoprolol and propranolol were more effective in reducing heart rate. Propranolol significantly reduced peak flow rate compared to labetalol. During the exercise, both isometric and dynamic, the heart rate and the blood pressure, both systolic and diastolic, of the treated patients were lower than those on placebo. There was little difference between the drugs in the influence on blood pressure, but metoprolol and propranolol were significantly more effective than labetalol in lowering the heart rate.

Antihypertensives and their impact on renal function

Antihypertensive agents possess many properties that could cause alterations in renal function. These are: alterations in systemic hemodynamics, changes in the renin-angiotensin aldosterone system, direct intrarenal effects, and alterations in salt and water metabolism. This article reviews the antihypertensive agents in general usage and major points are made concerning potential deleterious effects of methyldopa and nonselective beta-adrenergic blocking drugs on renal function. In particular, recent data are shown concerning the effects of labetalol on renal function indicating the absence of decrements in glomerular filtration rate and renal plasma flow in patients with normal renal function and in patients with mild to moderate renal insufficiency. A possible decrease in these parameters in patients with severe renal insufficiency is presented and discussed.

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.