Alpha and beta adrenergic blockade with orally administered labetalol in hypertension. Studies on blood volume, plasma renin and aldosterone and catecholamine excretion

Screening for primary aldosteronism in pregnancy

Primary aldosteronism, the most common secondary cause of hypertension is likely to be significantly underdiagnosed in pregnancy and is associated with high rates of adverse maternal and fetal outcomes. Normal pregnancy is associated with a rise in aldosterone and renin levels early in pregnancy making the aldosterone:renin ratio which is normally used to screen for primary aldosteronism, difficult to interpret. Additionally, many laboratories have moved from performing plasma renin activity to measurements of direct renin. Aldosterone, direct renin and aldosterone: renin ratios were determined in 9 women with primary aldosteronism and compared to levels in 33 women with chronic hypertension. All women with primary aldosteronism had a direct renin levels of less than 20 mU/L together with aldosterone:renin ratio of greater than 40. Values for direct renin were significantly lower, and the aldosterone:renin ratio was significantly higher in pregnancy in women with primary aldosteronism compared to women with chronic hypertension. Pregnant women with chronic hypertension who have a direct renin level less than 20 mU/L and aldosterone:renin ratio of greater than 40 should have close surveillance for maternal and fetal complications, and follow-up postpartum should be ensured for definitive testing.

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.

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.

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.

Cardiovascular regulation during administration of co-dergocrine to normal subjects

Whether and to what extent activation of peripheral presynaptic dopamine2-receptors may modulate the release of norepinephrine (NE) and so affect blood pressure (BP) in normal or hypertensive man is not clear. The hydrogenated ergotoxine derivative, co-dergocrine, given in effective antihypertensive rather than excessive experimental doses, has recently been shown to act predominantly as a peripheral dopamine2-receptor agonist in several species. Accordingly, BP regulation assessed has been in 8 normal men on placebo and after 3 weeks on codergocrine 4 mg/day. Co-dergocrine significantly reduced urinary NE excretion from 43 to 33 micrograms/24 h, supine and upright plasma NE 21 to 16 and 49 to 36 ng/dl, respectively, heart rate (-8 and -5%, respectively) and upright systolic BP, 115 to 102 mm Hg; upright diastolic BP also tended to be lower. A standard pressor dose of infused NE was lowered from 131 to 102 ng/kg/min, and the relationship between NE-induced changes in BP and concomitant NE infusion rate or plasma NE concentration was displaced to the left. Exchangeable sodium and plasma volume tended to be slightly decreased. Plasma and urinary electrolytes and epinephrine, plasma renin activity and aldosterone levels, pressor responsiveness to angiotensin II, the chronotropic responses to isoproterenol, and the NE-induced rise in BP, plasma clearance of NE, glomerular filtration rate and effective renal plasma flow were not consistently modified. The findings are consistent with effective peripheral dopamine2-receptor agonism by co-dergocrine in humans. Peripheral presynaptic dopaminergic activation may modulate sympathetic activity and BP in normal man.

Cardiovascular and metabolic profile during intervention with urapidil in humans

Increased sympathetic activity or vascular reactivity to norepinephrine or both may play a complementary role in the pathogenesis of essential hypertension. Therefore, blood pressure regulation and metabolic correlates of cardiovascular risk were evaluated in 19 normal subjects and in 13 subjects with essential hypertension receiving placebo and after 4 weeks of intervention with urapidil, an agent that was found experimentally to exert a combined central sympathetic and peripheral alpha-adrenergic receptor inhibition. In hypertensive patients, urapidil normalized the initially low norepinephrine pressor dose (+ 106%), mildly increased basal plasma norepinephrine levels (+36%), and markedly shifted the plasma norepinephrine concentration-blood pressure response curve (p less than 0.01). Blood pressure was decreased (p less than 0.001). In normal subjects, urapidil produced only mild increases in norepinephrine plasma levels (+22%) and norepinephrine pressor dose (+38%) and no change in blood pressure. Body weight, exchangeable sodium, and blood volume were unaltered or increased slightly. Heart rate; plasma epinephrine, renin, angiotensin II, basal aldosterone, and electrolyte levels; plasma clearances of norepinephrine and angiotensin II; pressor effects of angiotensin II; chronotropic responses to isoproterenol or a norepinephrine-induced rise in blood pressure; and urinary prostaglandin F2 alpha excretion, as well as serum lipoprotein fractions and glucose, insulin, and uric acid levels, were not significantly modified by urapidil. Prostaglandin E2 excretion tended to be increased. Aldosterone responsiveness to angiotensin II was increased by urapidil in normal (p less than 0.05) but not in hypertensive subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Antihypertensive and metabolic effects of nifedipine and labetalol alone and in combination in primary hypertension

In a randomised, double-blind, cross over trial, 25 patients with mild to moderate primary hypertension were given nifedipine 20-40 mg twice daily and labetalol 200-400 mg twice daily after a 4 week period on placebo, followed by the two drugs in combination. The BP during placebo therapy was 164/108 mmHg supine and 159/110 mmHg standing. After monotherapy with nifedipine for 6 weeks the supine BP was reduced by 18/13 mmHg and the standing BP by 20/12 mmHg; with labetalol the corresponding figures were 26/15 mmHg and 28/21 mmHg, respectively. The combined therapy induced a larger fall in BP, by 36/22 mmHg supine and by 39/24 mmHg standing; in 21 of 23 patients the BP became normal. The heart rate (HR) decreased during labetalol treatment alone and on the combined therapy. With nifedipine alone, the HR was unchanged in the supine position and increased on standing. Nifedipine increased plasma renin activity (PRA) and urinary aldosterone excretion (uA), whereas labetalol reduced both. During combination therapy, PRA and uA remained unchanged. There was a slight fall in HDL-cholesterol during treatment with labetalol alone and in combination with nifedipine. The fasting blood glucose increased slightly during treatment with each of the drugs, but neither caused a change in the concentrations of glycosylated haemoglobin A1, serum insulin, C-peptide, or plasma glucagon. Adverse effects as a rule were well tolerated and were related to the pharmacological effects of the drugs. Only 2 patients left the trial, both during labetalol treatment.

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)

Pharmacology of combined alpha-beta-blockade. I

Several compounds of the chemical class arylethanolamines have been shown to possess combined alpha- or vasodilator and beta-adrenoceptor blocking properties. The first drug was labetalol (AH5158)[5-(1-hydroxy-2)1-methyl-3-phenylpropyl(amino)-ethyl (salicylamide)]. Others include medroxalol, bucindolol and YM-09538, which differ from labetalol either by the nature of the substitution on the primary benzene ring and/or on the terminal nitrogen. All of these drugs are non-selective beta-blockers, except for bucindolol whose selectivity has not been carefully defined. The rationale for the development of this group of drugs was the knowledge that blockade of one adrenoceptor subtype causes reflex stimulation of the other, i.e. vasoconstriction after nonspecific beta-blockade and tachycardia after alpha-blockade. Since both of these compensatory responses act to prevent a fall in blood pressure, a relatively weak blockade of both receptor types should act synergistically to produce a lowering of blood pressure with minimal physiological disturbance. Haemodynamic studies have confirmed that the additional alpha-blocking properties of labetalol produce a pattern of haemodynamic changes unlike that of propranolol and other simple beta-adrenoceptor blocking agents. Peripheral vascular resistance, which falls acutely during the initial administration of the drug, tends to fall further during prolonged administration and the pulse rate tends to remain only slightly lower than pretreatment levels. In addition, at normal dose levels cardiac output is maintained by a compensatory increase in stroke volume. Thus, blood pressure is lowered largely by a reduction in vascular resistance, and although the heart rate falls significantly during exercise, the cardiac output is maintained by an increase in stroke volume. This pattern of events is different to that seen with beta-blocking agents which consistently reduce cardiac output during exercise. Currently labetalol is the only member of this group of drugs which is in established clinical use. Its antihypertensive efficacy has been confirmed in many studies and it has been shown to be effective in the management of both hypertensive emergencies and in the long term management of severe hypertension. It is particularly valuable in allowing a reduction in the number of drugs required for adequate blood pressure control. The early theoretical prediction that postural hypotension would occur with high doses is now acknowledged to be labetalol's major dose-limiting side effect. Most of the available pharmacokinetic data on labetalol were derived from studies which utilised a fluorimetric assay.(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.

Sympathetic nervous activity and the pressor effect of noradrenaline under chronic alpha-beta-adrenoceptor blockade with labetalol in hypertension

In 14 patients with essential hypertension, the influence of the alpha- and beta-adrenoceptor blocking drug labetalol on blood pressure, heart rate, plasma renin, plasma noradrenaline and pressor effect of exogenous noradrenaline was investigated during long-term treatment. During the initial four weeks of treatment, labetalol at a dose of 400 mg/day showed a slight effect only on supine blood pressure, whereas upright blood pressure was already lowered effectively after the second week of treatment (p less than 0.01). An increase in the mean dose to 850 mg/day had an additional blood pressure-lowering effect (p less than 0.001), whereby a preferential decrease of the orthostatic blood pressure was no longer apparent. Further increase in the mean dose to 1,000 mg/day at the end of the 12th week did not have an additional blood pressure-lowering effect. Body weight, plasma renin and plasma noradrenaline remained unchanged on labetalol treatment in the lowest and the highest dose. There was, however, an increased pressor effect of exogenous noradrenaline, i.e. an alpha-adrenoceptor antagonistic effect of labetalol was not detectable under these conditions. The cause of the increased pressor effect was a reduced elimination of noradrenaline from plasma, which is probably the consequence of an inhibition of the uptake 1 process by labetalol. During long-term treatment with the doses administered, the blood pressure-lowering effect of labetalol appears essentially to be the expression of the beta-adrenoceptor blocking properties of the drug.

Reversal of diuretic-induced increases in serum low-density-lipoprotein cholesterol by the betablocker pindolol

Seventeen patients with mild to moderate essential hypertension received during three consecutive 4 wk periods a matched placebo, the thiazide-like diuretic, clopamide in a low dosage of 5 mg/day, or this diuretic combined with the betablocker, pindolol in a low dosage of 10 mg/day. Compared to placebo conditions, clopamide monotherapy significantly increased serum low-density lipoprotein cholesterol (LDL-C) by 13% (p less than 0.025). Following addition of pindolol, serum LDL-C was restored to control values. These variations in serum LDL-C were unrelated to concomitant changes in blood pressure, plasma potassium, renin activity or aldosterone levels. Blood pressure in the supine position was reduced from 152/99 +/- 13/9 mm Hg (+ SD) to 141/93 +/- 15/7 mm Hg following diuretic-monotherapy and to 139/90 +/- 12/9 mm Hg following diuretic-betablocker combination treatment. These findings suggest that antihypertensive combination treatment with low doses of clopamide and pindolol is not only effective and well tolerated, but may also avoid the increase in serum LDL-C levels occurring when the thiazide-like diuretic is given alone.

The treatment of hypertension by labetalol--a new alpha- and beta-adrenoreceptor blocking agent

A new alpha- and beta-blocking agent, labetalol, was used to treat 50 hypertensive patients, 34 of them with refractory hypertension. A significant reduction in hypertension was achieved with relatively few adverse reactions. The combination of alpha and beta blockers in labetalol with their mutually opposing characteristics offers an interesting and promising approach to the control of hypertension.

The use of labetalol in Japan: results of multicentre clinical trials

1 The anti-hypertensive effects and safety of labetalol have been evaluated in multicentre clinical trials in Japan based on unified study protocols. The results of three studies are reported. 2 A total of 178 patients with essential hypertension were treated with labetalol for 12 weeks, 127 of them with labetalol alone (monotherapy) and the other 51 with labetalol plus diuretics (combined therapy). 3 Satisfactory antihypertensive effects were achieved in 76 of the 119 assessable patients in the monotherapy group and 25 of the 49 in the combined therapy group. The mean daily doses of labetalol were 329 mg in the monotherapy group and 374 mg in the combined therapy group. Seven patients (six in the monotherapy group; one in the combined therapy group) were withdrawn from the trials due to side-effects. 4 Sixty-one patients with hypertension were treated with labetalol alone or combined with diuretics for 6 months or longer. In most of these patients, good blood pressure control was achieved. No patients had to discontinue the treatment due to side-effects. The mean daily doses of labetalol were stabilised in and after week 8 of the treatment at an average of 260 mg in the monotherapy and 450 mg in the combined therapy. Tolerance to the anti-hypertensive effect did not develop. 5 Thirty patients with phaeochromocytoma were treated with labetalol and good blood pressure control was achieved in 21 of them. The effects of labetalol were better in patients with predominantly adrenaline-secreting tumours, and better in patients with sustained hypertensive type than in those with paroxysmal hypertensive type.

Intravenous labetalol in severe hypertension

1 Labetalol was administered by intravenous infusion or by the combination of intravenous bolus injection plus infusion to 15 patients with severe essential hypertension and to one with phaeochromocytoma. 2 With the infusion alone the reduction of arterial pressure was slow to develop and limited in degree, but with the combination of the bolus injection plus the infusion the reduction in pressure was more prompt, more pronounced and longer lasting. Apart from an uncomplicated syncopal attack in one patient, no serious side--effects were encountered. 3 Subsequent treatment with oral labetalol usually required the addition of a diuretic to control the blood pressure probably due to sodium and fluid retention during treatment with labetalol alone.

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.

Labetalol and propranolol in mild hypertensives: comparison of blood pressure and plasma volume effects

Labetalol administered in a small to moderate dose (first month 400 mg/day, second month average 585 mg/day) was effective in lowering blood pressure (BP) (-21/-18 mmHg, recumbent) in 11 of 13 mild essential hypertensives over an eight-week period, despite a significant (+294 ml) increase in plasma volume. The effect of propranolol (first month 160 mg/day, second month average 234 mg/day) was significantly less on both blood pressure (-9/-9 mmHg) and plasma volume (+98 ml), although the pre-propranolol BP was lower and the final BP achieved on the two medications was comparable (labetalol 147/89 mmHg, propranolol 145/89). Six patients who continued labetalol for periods of up to 14 months had persistent plasma volume expansion. Three of these, taking a higher dose of labetalol, developed resistance to the drug's antihypertensive effect. Addition of a diuretic restored antihypertensive efficacy and led to a fall in plasma volume. No such plasma volume expansion was seen in six patients who were followed on long term propranolol therapy. Some plasma volume expansion with the combined alpha- beta-adrenoceptor blocker labetalol may be appropriate to its vasodilator action. Provided this effect is not excessive, it appears not to lead to resistance to its antihypertensive action. Small to moderate doses of labetalol would, therefore, seem effective without concomitant diuretic. Such sole use of labetalol could help minimise orthostatic symptoms which can be a major side effect of combination therapy.

Effects of chronic alpha and beta adrenoceptor blockade with labetalol on plasma catecholamines and renal function in hypertension

Plasma catecholamines and renal function were evaluated in 18 patients with essential hypertension treated with the alpha and beta adrenoceptor blocking agent, labetalol. Following 6 weeks of labetalol therapy, blood levels of epinephrine and norepinephrine remained unaltered. Glomerular filtration rate and renal plasma flow were decreased similarly by about 20% (P less than 0.025). Tubular rejection fraction of sodium was increased by 36% (P less than 0.001) while sodium excretion was comparable to control conditions. Labetalol's potential to cause a mild reduction in kidney function should be considered, but may have no clinical consequences in most hypertensive patients receiving such treatment. The lack of increased plasma catecholamine levels during therapy supports the concept that labetalol's alpha-blocking potential is limited to post-junctional receptors, leaving the prejunctional feedback control of catecholamine release intact. Moreover, labetalol's blood pressure-lowering mechanism may be largely independent of changes in sympathetic nervous activity.

Experience with labetalol in essential hypertension

A study was carried out in 73 patients with mild or moderate hypertension to assess the effectiveness of treatment with labetalol. After a 2 to 4-week period on placebo, patients received 200 mg labetalol daily for 4 weeks, after which time dosage was doubled if the blood pressure was not satisfactorily controlled. Treatment was continued for a further 4 weeks and was followed by another period on placebo. Pre-treatment levels of 157/99 mmHg were significantly reduced after 2 weeks, and after 4 weeks the mean reduction was 14/8 mmHg. Half the patients had their dosage increased to 400 mg daily. At the end of the 8-week active treatment period, 80% were adequately controlled, the mean reduction in blood pressure being 22/12 mmHg compared with placebo values. Heart rate was significantly reduced from 78 to 69 beats per min during labetalol therapy. The reduction in blood pressure was similar whether or not patients had been previously treated or untreated, but heart rate was reduced more in the previously treated group. Four weeks after the end of labetalol therapy blood pressure and heart rate had increased but were less than during the initial placebo period and did not give rise to any severe problems.

Effect of oral labetalol on plasma catecholamines, renin and aldosterone in patients with severe arterial hypertension

Arterial blood pressure and plasma catecholamines, renin activity and aldosterone concentration in 12 patients with severe essential hypertension were studied before and after combined alpha- and beta-adrenergic receptor blockage induced by oral labetalol treatment for 2 months. Furosemide in a fixed dose was employed as a basic antihypertensive agent throughout the study. Blood pressure was adequately controlled in only 6 patients. Mean body weight increased by 1.8 kg and there was a rise in body weight which was inversely correlated with the fall in standing mean blood pressure. The mean plasma noradrenaline concentration decreased from 0.30 to 0.20 ng/ml, whereas plasma adrenaline did not change significantly. Plasma renin activity and aldosterone concentration varied greatly, but the mean values did not change significantly. Change in body weight was correlated inversely with changes in plasma noradrenaline and renin. The results suggest that labetalol, through its combined alpha- and beta-adrenergic receptor blocking action, induces a rise in body weight, probably due to sodium and fluid retention, which partly counterbalances the antihypertensive effect of labetalol, and partly modifies both renin and sympathetic nervous activity.

Increased catecholamine excretion after labetalol therapy: a spurious effect of drug metabolites

Patients with essential hypertension were treated for four weeks with the alpha- and beta-adreno-receptor blocking agent labetalol. Urinary excretion of total catecholamines, metanephrine plus normetanephrine and vanillylmandelic acid was measured with various methods before and during treatment. An unidentified substance interfering with the fluorimetric method for catecholamines and the photometric assay for metanephrines caused falsely high values of those substances. Using appropriate methodology no changes of total catecholamines, metanephrine plus normetanephrine and vanillylmandelic acid excretion were found after labetalol therapy. Our findings are important in preventing errors in the diagnosis of pheochromocytoma as well as in the evaluation of the effects of labetalol on the sympathetic nervous system in man.

[Acute combined alpha- and beta-adrenergic blockade in essential hypertension: effects on blood pressure, renal function, renin, and aldosterone]

In seven patients with uncomplicated essential hypertension the effects of an acute alpha-adrenergic blockade, alone and combined with a chronic beta-adrenergic blockade, on blood pressure, renal function as measured by standard clearance methods, plasma renin activity, and plasma aldosterone were evaluated. Acute alpha-adrenergic blockade with phentolamine (20 mg by intravenous infusion) significantly enhanced the antihypertensive effect of chronic beta-adrenergic blockade with slow-oxprenolol (160 mg/ day X 14 days) (- 14.5% verus - 7.4% for pulse pressure, - 12.4% versus - 6.0% for diastolic pressure, 2 alpha less than 0.05). Under combined adrenergic blockade renal plasma flow increased, glomerular filtration rate and filtration fraction decreased (2 alpha less than 0.05 each), whereas the fractional clearances of sodium, potassium, free water, and solute load remained unchanged. The activation of the renin-angiotensin-axis, elicited by alpha-adrenergic blockade alone, was suppressed by the preceding beta-adrenergic blockade. These findings demonstrate a favourable antihypertensive action of a combined blockade of alpha- und beta-adrenergic receptor sites without untoward side effects on renal function or the renin-angiotensin-axis.