Comparative study of the ventilatory effects of three beta 1-selective blocking agents in asthmatic patients

The safety of cardioselective β1-blockers in asthma: literature review and search of global pharmacovigilance safety reports

INTRODUCTION

Beta-blockers are key in the management of cardiovascular diseases but blocking airway β2-receptors can cause severe and sometimes fatal bronchoconstriction in people with asthma. Although cardioselective β1-blockers may be safer than non-selective β-blockers, they remain relatively contraindicated and under-prescribed. We review the evidence of the risk associated with cardioselective β1-blocker use in asthma.

METHODS

We searched "asthma" AND "beta-blocker" in PubMed and EmbaseOvid from start to May 2020. The World Health Organization (WHO) global database of individual case safety reports (VigiBase) was searched for reports of fatal asthma or bronchospasm and listed cardioselective β1-blocker use (accessed February 2020). Reports were examined for evidence of pre-existing asthma.

RESULTS

PubMed and EmbaseOvid searches identified 304 and 327 publications, respectively. No published reports of severe or fatal asthma associated with cardioselective β1-blockers were found. Three large observational studies reported no increase in asthma exacerbations with cardioselective β1-blocker treatment. The VigiBase search identified five reports of fatalities in patients with pre-existing asthma and reporting asthma or bronchospasm during cardioselective β1-blocker use. Four of these deaths were unrelated to cardioselective β1-blocker use. The circumstances of the fifth death were unclear.

CONCLUSIONS

There were no published reports of cardioselective β1-blockers causing asthma death. Observational data suggest that cardioselective β1-blocker use is not associated with increased asthma exacerbations. We found only one report of an asthma death potentially caused by cardioselective β1-blockers in a patient with asthma in a search of VigiBase. The reluctance to use cardioselective β1-blockers in people with asthma is not supported by this evidence.

Evolution of β-blockers: from anti-anginal drugs to ligand-directed signalling

Sir James Black developed β-blockers, one of the most useful groups of drugs in use today. Not only are they being used for their original purpose to treat angina and cardiac arrhythmias, but they are also effective therapeutics for hypertension, cardiac failure, glaucoma, migraine and anxiety. Recent studies suggest that they might also prove useful in diseases as diverse as osteoporosis, cancer and malaria. They have also provided some of the most useful tools for pharmacological research that have underpinned the development of concepts such as receptor subtype selectivity, agonism and inverse agonism, and ligand-directed signalling bias. This article examines how β-blockers have evolved and indicates how they might be used in the future.

Absence of respiratory effects with ivabradine in patients with asthma

AIM

beta-Blockers are commonly prescribed for stable angina and are recommended as initial therapy. However, beta-blockers are contraindicated in patients with obstructive airway disease because of a risk of bronchoconstriction. Ivabradine is a specific heart rate-lowering agent that acts via I(f) pacemaker channels in the sinoatrial node with no beta-adrenoreceptor activity. Ivabradine has been recently approved for the treatment of stable angina. This study assessed the effects of repeated administration of ivabradine on lung function in patients with asthma.

METHODS

In this double-blind, placebo-controlled, crossover study, 20 subjects with asthma received either oral ivabradine 10 mg b.i.d. or placebo for 4.5 days. Forced expiratory volume in 1 s (FEV(1)) and peak expiratory flow rate (PEFR) were designated as the main outcome variable. Diary cards were used to monitor asthma symptoms on a five-point scale, rescue medication usage, and adverse events.

RESULTS

There were no significant differences in mean variation of FEV(1) (ivabradine P = 0.664; placebo P = 0.652) or PEFR (ivabradine P = 0.153; placebo P = 0.356) from baseline following administration of ivabradine. There was also no significant difference in maximum percent variation in FEV(1) or PEF between treatment groups (P = 0.994; FEV(1) and P = 0.704; PEF). On a similar note, there was no significant difference in asthma symptoms or rescue medication usage reported between the two groups. Adverse events were generally mild-to-moderate in intensity and no cardiovascular or serious adverse events were recorded.

CONCLUSIONS

This study confirms that ivabradine does not affect respiratory function or symptoms in patients with asthma and therefore represents a valuable therapeutic alternative to beta-blockers for treating patients with stable angina and asthma.

Cardioselective beta-blocker use in patients with reversible airway disease

BACKGROUND

Beta-blocker therapy has mortality benefit in patients with hypertension, heart failure and coronary artery disease, as well as during the perioperative period. These drugs have traditionally been considered contraindicated in patients with reversible airway disease.

OBJECTIVES

To assess the effect of cardioselective beta-blockers on respiratory function of patients with reversible airway disease. Reversible airway disease was defined as asthma or chronic obstructive pulmonary disease with a reversible obstructive component.

SEARCH STRATEGY

A comprehensive search of EMBASE, MEDLINE and CINAHL was performed using the Cochrane Airways Group registry to identify randomized blinded placebo-controlled trials from 1966 to February, 2000. The search was completed using the terms: asthma*, bronchial hyperreactivity*, respiratory sounds*, wheez*, obstructive lung disease* or obstructive airway disease*, and adrenergic antagonist*, sympatholytic* or adrenergic receptor block*. We did not exclude trials on the basis of language.

SELECTION CRITERIA

Randomized, blinded, placebo-controlled trials of single dose or longer duration that studied the effects of cardioselective beta-blockers on the forced expiratory volume in 1 second (FEV1), symptoms and use of short-acting inhaled beta-agonists, in patients with reversible airway disease. Reversible airway disease was documented by response to methacholine challenge, by an increase in FEV1 of at least 15% to beta-agonist administration, or the presence of asthma as defined by the American Thoracic Society.

DATA COLLECTION AND ANALYSIS

Two independent reviewers extracted data from the selected articles, reconciling differences by consensus. Cardioselective beta-blockers were divided into 2 groups, those with or without intrinsic sympathomimetic activity (ISA). Two interventions studied were the administration of beta-blocker, given either as a single dose or for longer duration, and the use of beta-agonist given after the study drug.

MAIN RESULTS

Nineteen studies for single-dose treatment and 10 for treatment of longer duration met selection criteria. The patients had mild-moderate airways obstruction. For cardioselective beta-blockers taken as a group, administration of a single dose was associated with a 7.98% (CI, 6.19 to 9.77%) reduction in FEV1, but with a 13.16% (CI, 10.76 to 15.56%) increase in beta-agonist response, as compared to placebo. There was no increase in symptoms. After treatment lasting a few days to a few weeks, there was no decrement in FEV1 compared to placebo and no increase in symptoms or inhaler use. Regular use of cardioselective beta-blockers without ISA produced a 13.13% (CI, 5.97 to 20.30) increase in beta-agonist response compared to placebo, a response not seen with beta-blockers containing ISA (-0.60% [CI, -11.7 to +10.5%]).

REVIEWER'S CONCLUSIONS

Cardioselective beta-blockers, given to patients with mild-moderate reversible airway disease, do not produce clinically significant adverse respiratory effects in the short term. It is not possible to comment on their effects in patient with more severe or less reversible disease, or on their effect on the frequency or severity of acute exacerbations. Given their demonstrated benefit in conditions such as heart failure, coronary artery disease and hypertension, cardioselective beta-blockers should not be withheld from patients with mild-moderate reversible airway disease.

Beta-adrenergic-blocking agents in bronchospastic diseases: a therapeutic dilemma

Cardioselective beta-blockers should be administered starting with a low dosage under direct medical observation. Bronchodilators should be readily available or may be coadministered. Because of several advantages, agents such as metoprolol, atenolol, and, in some cases, esmolol should be the first agents considered. In contrast to noncardioselective agents, if bronchospasm occurs, the effect of cardioselective agents is believed to be easier to reverse. Clinicians should avoid noncardioselective beta-blockers in asthmatics, even in small doses, such as those administered as eye drops. For asthmatic patients who are intolerant to noncardioselective beta-blockers, switching to a cardioselective beta-blocker might be a safe alternative. The significance of beta2-blockade usually varies with the patient's ventilatory condition, with more serious consequences being anticipated in patients with more severe asthma.

Selectivity of acebutolol, atenolol, and metoprolol in healthy volunteers estimated by the extent the drugs occupy beta 2-receptors in the circulating plasma

The selectivity of acebutolol, atenolol, and metoprolol in healthy volunteers was estimated by determining the extent to which the drugs occupied beta 1-receptors of rabbit lung and beta 2-receptors of rat reticulocytes in the circulating plasma after drug intake. This ex vivo method had the advantage of including all drug components contributing to the drug-receptor equilibrium in vivo and of excluding the factors regulating organ sensitivity to catecholamine stimulation. The oral doses of 400 mg acebutolol, 100 mg atenolol, and 100 mg metoprolol were administered to six healthy male volunteers using a double-blind, randomized, and cross-over study design. The three drugs occupied beta 1-receptors to a similar extent at 2 hours after drug intake. The receptor fraction occupied by metoprolol at 3 to 8 hours after drug intake was usually smaller, however (analysis of variance for repeated measures, P < .05) than that of the other drugs. Acebutolol occupied significantly larger fractions of beta 2-receptors (analysis of variance for repeated measures, P < .05) than did atenolol and metoprolol. Therefore, at an identical beta 1-receptor occupancy, the beta 2-receptor occupancy of acebutolol was larger than that of the other agents. Apparently, active metabolites decreased markedly the selectivity of acebutolol, but not that of metoprolol. The receptor occupancy of the agents was well in agreement with the literature concerning the selectivity, intensity, and time-course of drug actions after identical doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative evaluation of cardioselectivity of metoprolol OROS and atenolol: a double-blind, placebo-controlled crossover study

Cardioselectivity of a single oral dose of metoprolol oral osmotic (OROS) (14/190 mg) and atenolol (100 mg) was compared in 12 patients with reversible obstructive airway disease by assessing the dose-response curve to increasing doses of inhaled salbutamol. The beta-blocking activity of the two drugs, which was determined by measuring heart rate, blood pressure, and derived indexes at peak plasma drug levels, was similar. Both metoprolol and atenolol significantly reduced forced vital capacity and peak expiratory flow, with no difference between drugs. Atenolol but not metoprolol also significantly reduced forced expiratory volume in 1 second and specific airway conductance. Both metoprolol and atenolol shifted the dose-response curve of specific airway conductance to the right. The results indicate that the new OROS delivery system for metoprolol, which produces a relatively constant plasma drug level, provides a cardioselectivity comparable to or greater than that of atenolol at maximum plasma levels.

Pharmacologic aspects of intrinsic sympathomimetic activity in beta-blocking drugs

The possession of intrinsic sympathomimetic activity (ISA) by a beta-adrenoceptor blocking drug results in a number of different pharmacologic properties. Most profound are the central hemodynamic effects. A drug with a significant degree of ISA results in less of a decrease in heart rate at rest and cardiac output, and, at least partly because of this, less of a decrease in peripheral blood flow. If prevailing sympathetic tone is low enough (e.g., during sleep) and the degree of ISA is sufficient, an increase in heart rate may be seen from an ISA-possessing drug. If the drug possesses beta 2 ISA, then a peripheral vasodilation action from stimulation of beta 2 vasodilator receptors may also be relevant. If high levels of exercise and full dosages of the drugs are used, a beta-blocking drug with ISA produces less of a decrease in heart rate. In asthmatic subjects, the modest beta-stimulant action on bronchial smooth muscle is not important, as these patients are potentially sensitive to any receptor blockade. Isoprenaline responses are inhibited to a similar degree compared with inhibition of exercise tachycardia, by nonselective drugs with and without ISA, whereas beta 1 selective agents produce much less inhibition of isoprenaline-induced tachycardia. A drug with ISA "down regulates" beta receptors; thus, when the drug is withdrawn there is no post-beta-blocking drug hypersensitivity in contrast to agents without ISA. There is evidence that ISA results in less of a disturbance in certain metabolic processes, particularly lipid metabolism and the metabolism of liver-metabolized drugs.

A comparative study on the ventilatory and haemodynamic effects of xamoterol and atenolol in asthmatic patients

The effects of single oral doses of atenolol 50 mg and xamoterol 200 mg (a recently developed partial beta 1-adrenoceptor agonist) on lung function, heart rate and blood pressure were investigated in 11 patients with asthma. Xamoterol caused a significant increase in heart rate and systolic blood pressure, which changes are consistent with the partial beta 1-adrenoceptor agonist activity of this drug. Atenolol induced a significant decrease in FEV1 and the forced vital capacity (FVC); there was a non-significant change in FEV1 and FVC after xamoterol. There was no significant difference between the effects of atenolol and xamoterol of FEV1 and FVC. Bronchospasm induced by atenolol 50 mg and xamoterol 200 mg was completely reversed by inhalation of the beta 2-adrenoceptor agonist terbutaline to a cumulative dose of 4.0 mg.

Influence of beta blockade and intrinsic sympathomimetic activity on hemodynamics, inotropy and respiration at rest and during exercise

The degree of intrinsic sympathomimetic activity (ISA) is reported to influence the effects of beta blockade at rest, but the effects during exercise are not well documented. Heart rate, blood pressure and left ventricular (LV) function (as assessed by systolic time intervals) were measured at rest and during upright bicycle exercise as well as with flow-volume spirometry at rest in 13 healthy volunteers. The measurements were performed before and 4 and 24 hours after a single oral dose of pindolol (10 mg), nadolol (80 mg) and acebutolol (400 mg) in a double-blind, randomized, crossover manner. All drugs reduced heart rate, but nadolol had the most pronounced and longest bradycardic effect at rest. Diastolic blood pressure was only slightly influenced by the drugs, whereas systolic pressure was significantly lower compared with control values, especially during exercise (p less than 0.001). Neither preejection period (PEP) nor LV ejection time (LVETc) was changed at rest after pindolol, but PEP increased and LVETc decreased significantly after nadolol (p less than 0.05 for PEP and p less than 0.01 for LVETc) and acebutolol (p less than 0.05 for both). During exercise, PEP and LVET were significantly longer after all 3 drugs compared with control values. Only nadolol, which lacks ISA, significantly decreased expiratory flow values (p less than 0.05). Thus, unlike the other beta blockers, pindolol (with strong ISA) did not depress LV function at rest, while during exercise all 3 beta blockers had equal adverse effects. The degree of ISA appears to be important in determining the hemodynamic effects of beta-blocking drugs.

Metoprolol. An updated review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy, in hypertension, ischaemic heart disease and related cardiovascular disorders

During the intervening years since metoprolol was first reviewed in the Journal (1977), it has become widely used in the treatment of mild to moderate hypertension and angina pectoris. Although much data have accumulated, its precise mechanisms of action in these diseases remain largely uncertain. Optimum treatment of hypertension and angina pectoris with metoprolol is achieved through dose titration within the therapeutic range. It has been clearly demonstrated that metoprolol is at least as effective as other beta-blockers, diuretics and certain calcium antagonists in the majority of patients. Although a twice daily dosage regimen is normally used, satisfactory control can be maintained in many patients with single daily doses of conventional or, more frequently, slow release formulations. Addition of a diuretic may improve the overall response rate in hypertension. Several controlled trials have studied the effects of metoprolol administered during the acute phase and after myocardial infarction. In early intervention trials a reduction in total mortality was achieved in one moderately large trial of prolonged treatment, but in another, which excluded patients already being treated with beta-blockers or certain calcium antagonists and where treatment was only short term, mortality was significantly reduced only in 'high risk' patients. Overall results with metoprolol have not demonstrated that early intervention treatment in all patients produces clinically important improvement in short term mortality. Thus, the use of metoprolol during the early stages of myocardial infarction is controversial, largely because of the requirement to treat all patients to save a small number at 'high risk'. This blanket coverage approach to treatment may be more justified during the post-infarction follow-up phase since it has been shown that metoprolol slightly, but significantly, reduces the mortality rate for periods of up to 3 years. Metoprolol is generally well tolerated and its beta 1-selectivity may facilitate its administration to certain patients (e.g. asthmatics and diabetics) in whom non-selective beta-blockers are contraindicated. Temporary fatigue, dizziness and headache are among the most frequently reported side effects. After a decade of use, metoprolol is well established as a first choice drug in mild to moderate hypertension and stable angina, and is beneficial in post-infarction patients. Further study is needed in less well established areas of treatment such as cardiac arrhythmias, idiopathic dilated cardiomyopathy and hypertensive cardiomegaly.

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

Acebutolol is a new hydrophilic, cardioselective beta-adrenergic-blocking agent that possesses partial agonist and membrane-stabilizing activities. In the treatment of mild to moderate essential hypertension, once-daily acebutolol as monotherapy provides effective control in a large majority of patients and produces a further reduction in blood pressure when used concomitantly with diuretics. Acebutolol is as effective as other beta-blocking agents, and in a large, double-blind, parallel study against propranolol was found to cause less reduction in heart rate, and fewer neurologic side effects and patient withdrawals due to adverse effects. Oral acebutolol is also effective in suppressing premature ventricular contractions, and in small numbers of patients generally beneficial results were obtained in supraventricular and ventricular arrhythmias with intravenous administration. These salutary effects are attributable to beta blockade. Controlled clinical trials documented the antianginal actions of oral acebutolol in chronic stable angina pectoris; its efficacy in this regard is comparable to that of other beta-blocking agents. The drug produces smaller decreases in heart rate and cardiac output and alterations in peripheral vascular hemodynamics than beta-blocking drugs without partial agonist activity, and because of its cardioselectivity, it may be used cautiously in patients with bronchospastic disease. Acebutolol has minimal metabolic effects and does not elevate levels of blood lipids during long-term therapy; high-density-lipoprotein cholesterol increased with acebutolol in a small number of patients.

Effects of esmolol on airway function in patients with asthma

In a double-blind, randomized, crossover study in ten patients with asthma, the effects on specific airway resistance of esmolol, a new ultra-short-acting beta 1-selective adrenoceptor blocker, were compared with those of placebo. Specific airway resistance was measured during increasing doses of esmolol infusion, during dry air provocation tests, and following isoproterenol inhalation. These same studies were later carried out on six of ten patients following intravenous propranolol infusion. All patients were able to tolerate the maximum dose of esmolol (300 micrograms/kg/min); treatment differences between esmolol and placebo were not found. In contrast, intravenous propranolol produced marked symptomatic bronchoconstriction after the lowest dose (1 mg) in two of six patients. Esmolol produced slight but statistically significant enhancement of patients' sensitivity to dry air provocation. Similarly, a slight but significant inhibition of bronchomotor sensitivity to isoproterenol was noted during esmolol infusion. After infusion of 5 mg of intravenous propranolol, one of four patients had a clinically significant increase in sensitivity to dry air. It is concluded that esmolol, because of its short duration of action and relative lack of effect on airway resistance, may be preferred over propranolol in patients with asthma who require treatment with an intravenous beta-blocking agent.

Comparative study of the respiratory effects of two beta 1-selective blocking agents atenolol and bevantolol in asthmatic patients

Seven asthmatic patients were given a single placebo tablet in a first test session and then in two subsequent double blind sessions they randomly received 400 mg bevantolol or 100 mg atenolol, with at least 2 days between each of the sessions. Neither beta-blocker had any significant effect on FVC as compared to the placebo. FEV 1, however, was significantly lower 2 and 3 h after atenolol or bevantolol; there was no significant difference between the effects of the two drugs on FEV 1. Peak expiratory flow rate was reduced by bevantolol but not by atenolol, the difference reaching significance after 3 h. Fenoterol inhalation at the end of each test session always enhanced pulmonary performance, but to a lesser extent after bevantolol than after placebo or atenolol. A slower heart rate was recorded 2, 3, and 4 h after bevantolol and 3 and 4 h after atenolol; the mean 2-h value was significantly lower with atenolol than with bevantolol. No patient suffered any adverse effect. Bevantolol may be slightly less selective than atenolol.

Ancillary pharmacologic properties of acebutolol: cardioselectivity, partial agonist activity, and membrane-stabilizing activity

Acebutolol, a new beta-blocking agent, possesses the ancillary pharmacologic properties of cardioselectivity and partial agonist and membrane-stabilizing activities. Compared to propranolol at equipotent doses, acebutolol produces less bronchoconstriction and preserves the bronchodilator response to isoprenaline. Similarly, acebutolol has less of an effect on peripheral vascular hemodynamics than does propranolol. Because of partial agonist activity, acebutolol produces a lesser reduction in heart rate and cardiac output than do propranolol and atenolol and has been found to have minimal effects on lipoprotein metabolism. Acebutolol may be the only beta-blocking agent that demonstrates some membrane-stabilizing activity at clinically achievable plasma concentrations. The ancillary pharmacologic properties of cardioselectivity and partial agonist activity are distinct and offer definite advantages to selected patients, particularly patients with respiratory disease, in whom cardioselective acebutolol, particularly at low doses, can minimize patient risk. The ancillary property of membrane-stabilizing activity may also guide therapy in selected patients.

Acebutolol: ten years of experience

During 10 years of clinical use involving almost 3 million patient-years, acebutolol has become established as a remarkably safe and well-tolerated beta-blocking agent, effective in treating essential hypertension and cardiac arrhythmias. The existence of a long-lived active metabolite (diacetolol) confers a 24-hour duration of action, which permits effective use of a once-daily regimen, particularly for hypertension. Acebutolol has low lipid solubility and low protein binding; the former property reduces the risk of central side effects, and the latter means that displacement interactions with other drugs are unlikely. Because acebutolol and its metabolite normally have both renal and hepatic excretion pathways, an alternative pathway is available should either be compromised through disease. Acebutolol is cardioselective, and clinical use has borne out the low incidence of bronchospasm in patients with impaired lung function. The possession of intrinsic sympathomimetic activity (ISA) leads to only modest reductions in cardiac output, which in turn reduces the chance of excessive bradycardia and the likelihood of precipitating heart failure. A combination of selectivity and ISA may be responsible for the low incidence of tiredness and cold extremities observed with acebutolol compared with other beta blockers. The unique pharmacologic and pharmacokinetic profile of acebutolol confers several therapeutic advantages and may be responsible for the generally low level of side effects experienced in clinical use.

Ventilatory and haemodynamic effects of prenalterol and terbutaline in asthmatic patients

In 8 asthmatic patients a comparative study was performed of the ventilatory and haemodynamic effects of the beta 1-receptor stimulator prenalterol and the beta 2-receptor stimulator terbutaline infused in increasing doses after a placebo. Terbutaline caused a dose-dependent decrease in diastolic blood-pressure (BP) and an increase in systolic BP and heart-rate (HR), while mean arterial pressure (MAP) did not change. Prenalterol produced a dose-dependent increase in MAP and systolic BP, while diastolic BP was unaffected. HR was increased only by the largest dose of prenalterol. The haemodynamic effects of the terbutaline infusion can be explained by a reflex response to the vasodilatation induced by stimulation of the vascular beta 2-receptors, while the effects of prenalterol can mainly be accounted for by a direct action on beta 1-receptors in the heart. These observations show that the cardiac side-effects of beta 2-agonists cannot be avoided by producing more selective agonists. Terbutaline caused a dose-dependent increase in the ventilatory indices. Prenalterol in larger doses caused a limited but significant increase in the ventilatory indices, comparable to the decrease in ventilation caused by the beta 1-selective blocker metoprolol. These findings suggest that the ventilatory effects of metoprolol and prenalterol are mediated via beta 1-receptors in the airways, which apparently play a functional role in asthma.

Ventilatory and haemodynamic effects of terbutaline infusion during beta 1-selective blockade with metoprolol and acebutolol in asthmatic patients

A double-blind, placebo-controlled study of the haemodynamic and ventilatory effects of two beta 1-selective adrenoceptor blockers and their interaction with the beta 2-adrenoceptor agonist terbutaline was carried out in eight asthmatic patients. One hour after intake of placebo, metoprolol 100 mg or acebutolol 400 mg, increasing doses of terbutaline were infused. Before and one hour after ingestion of the medication and after each infusion of terbutaline, ventilatory and haemodynamic indices were measured. The two beta-blocking agents caused equal changes in basal ventilatory and haemodynamic indices. Terbutaline infusion caused a dose dependent increase in forced expiratory volume in one second (FEV1) and peak expiratory flow rate (PEFR), both during placebo and beta-blockade. Metoprolol did not affect the terbutaline-induced bronchodilatation. During acebutolol medication, however, the increase in FEV1 and PEFR induced by terbutaline was partly inhibited. Terbutaline infusion during placebo caused a dose-dependent increase in heart rate (HR) and systolic blood pressure (BP), and a decrease in diastolic BP. During acebutolol medication, these haemodynamic effects of terbutaline were completely blocked, but during metoprolol medication terbutaline still caused small changes in the same direction as during placebo, presumably because the vasodilator action of terbutaline was not inhibited. A negative correlation was found between the plasma levels of acebutolol and its metabolite N-acetyl acebutolol at the end of the study and changes in FEV1 and PEFR induced by terbutaline during acebutolol therapy as compared with placebo. The ventilatory and haemodynamic findings suggest a lower degree of beta 1-selectivity after oral administration of acebutolol as compared to metoprolol.