Pirbuterol: a new oral sympathomimetic amine for the treatment of congestive heart failure

Should acute treatment with inhaled beta agonists be withheld from patients with dyspnea who may have heart failure?

In patients with dyspnea, prehospital and emergency providers make therapeutic decisions before a diagnosis is established. Inhaled beta-2 agonists are frontline treatment for patients with dyspnea due to asthma or chronic obstructive pulmonary disease (COPD) exacerbations. However, these agents have been associated with increased adverse events when administered chronically to heart failure patients. Our goal was to determine the safety and efficacy of acute administration of inhaled beta-2 agonists to patients with heart failure. MEDLINE and EMBASE searches were performed using the terms "beta agonists," "albuterol," "congestive heart failure," and "pulmonary edema." Bibliographies of relevant articles were searched. Only studies addressing acute effects of beta-2 agonists were included for analysis. Twenty-four studies comprising 434 patients were identified that addressed the acute delivery of beta-2 agonists in subjects with heart failure--five studies with inhaled administration and 19 with systemic administration. No study directly evaluated the effects of inhaled beta-2 agonists to patients with acutely decompensated heart failure. Treatment of heart failure patients with beta-2 agonists resulted in transient improvements in pulmonary function and cardiovascular hemodynamics. Only one investigation reported an association between beta-2 agonist use and an increase in malignant dysrhythmias. Investigations in animal models of heart failure and acute lung injury demonstrated resolution of pulmonary edema with beta agonist administration. There is insufficient evidence to suggest that acute treatment with inhaled beta-2 agonists should be avoided in patients with dyspnea who may have heart failure. Based on small studies and indirect evidence, administration of beta-2 agonists to patients with heart failure seems to improve pulmonary function, cardiovascular hemodynamics, and resorption of pulmonary edema. Although an increase in adverse effects with the use of beta-2 agonists cannot be ruled out based on these data, there was no evidence of an increase in clinically significant dysrhythmias, especially when administered by inhalation. Based on these findings, further study should focus on the clinical outcomes of patients with acutely decompensated heart failure who are treated with inhaled beta-2 agonist therapy.

Safety and efficacy of carvedilol in severe heart failure. The U.S. Carvedilol Heart Failure Study Group

BACKGROUND

Many patients remain markedly symptomatic despite optimal current therapy for heart failure. Beta-blockers have often been viewed as contraindicated in this group because of their potential adverse short-term effects on cardiac function.

METHODS AND RESULTS

One hundred thirty-one patients with severe congestive heart failure were enrolled into a double-blind, placebo-controlled study of the vasodilating beta-blocker carvedilol. All patients had symptomatic, advanced heart failure while on standard triple therapy, as evidenced by a mean ejection fraction of 0.22, marked reduction in distance traveled in a 6-minute corridor walk test, and severe impairment in quality of life measured by the Minnesota Living With Heart Failure Questionnaire. After a 2-week, open-label test of 6.25 mg twice daily carvedilol, 105 patients were randomized (2:1) to receive either carvedilol (up to 25 mg twice daily, n = 70) or matching placebo (n = 35) for 6 months while background therapy with digoxin, diuretics, and an angiotensin-converting enzyme inhibitor remained constant. Ten patients (8%) did not complete the open-label period because of adverse events and 11.4% in both the carvedilol and placebo groups dropped out in the double-blind phase. The study was terminated early by the Data Safety and Monitoring Board and follow-up evaluation was therefore aborted before the projected number of patients and follow-up time was achieved. Quality of life, which was the primary endpoint, improved similarly in the carvedilol and placebo groups, whereas the global assessment by the physicians and the patient exhibited a better response to carvedilol (P < .05). Hospitalization and mortality rate were too low to evaluate a difference, and exercise time and New York Heart Association classification did not change significantly in response to the drug. Left ventricular ejection fraction rose significantly (+0.09) in the carvedilol group compared with the placebo group (+0.02, P = .004).

CONCLUSION

The beta-blocker carvedilol can be safely employed in patients with severe heart failure. Improved left ventricular function with a trend for some improvement in symptoms combined with the experience with the drug in the larger population of less severe patients in this multicenter trial suggests that carvedilol may have a favorable long-term effect in heart failure of diverse severity.

Angiotensin-converting enzyme inhibition, the sympathetic nervous system, and congestive heart failure. The Australian Zestril (Lisinopril) Study Group

Catecholamines have been found to be powerful indicators of prognosis in patients with congestive heart failure. However, it is uncertain whether catecholamines are a marker for decreased cardiac performance or part of the pathologic process. Catecholamines, exogenously derived beta-adrenergic stimulants, and drugs that amplify sympathetic responsiveness produce early hemodynamic benefits, but do not appear to provide long-term improvement in terms of symptoms or exercise tolerance, whereas blockade of the beta-adrenoceptor appears to have little early benefit but may improve long-term prognosis. This suggests that in the long term, increased catecholamine levels may be deleterious. Angiotensin-converting enzyme (ACE) inhibitors can modulate circulating catecholamines, and the persistence and degree of ACE inhibition may be important not only in reducing catecholamines, but possibly also in reducing mortality in heart failure. It appears that ACE inhibitors definitely reduce mortality in congestive heart failure. It remains to be documented whether the persistence and degree of ACE inhibition is a factor in this effect, and, thus, comparison of short- with long-acting ACE inhibitors and study of the dosage of ACE inhibitors are of importance. The extent to which modulation of the sympathetic nervous system by ACE inhibitors is an important mechanism in their effect in reducing mortality remains to be established.

Ventricular arrhythmia in congestive heart failure

The importance of ventricular arrhythmia is based on its association with sudden death. In certain groups of patients, ventricular arrhythmia--primarily runs of nonsustained ventricular tachycardia (NSVT)--is associated with an increased risk for sudden death. Although this relationship has been most often reported in patients with recent myocardial infarction, it has also been recognized in patients with dilated cardiomyopathy, regardless of etiology. Therefore, ventricular arrhythmia is common in patients with CHF due to cardiomyopathy. A number of studies have reported that 70-95% of patients with cardiomyopathy and congestive heart failure (CHF) have frequent ventricular premature beats, and 40-80% will manifest runs of NSVT. Many factors are responsible for ventricular arrhythmia in such patients, including structural abnormalities, electrolyte imbalance, hemodynamic impairment, activation of neurohormonal mechanisms, and pharmacologic therapy. Many studies have reported a high yearly mortality in patients with cardiomyopathy and CHF; greater than 40% of deaths are sudden, most often the result of sustained ventricular tachyarrhythmia. Most studies have noted an association between presence (and frequency) of NSVT and risk of sudden cardiac death in these patients. Unfortunately, other techniques--such as the signal-averaged electrocardiogram and electrophysiologic testing--are not helpful in identifying the individual at risk. Although several drug interventions will reduce mortality from progressive CHF, these drugs have not been shown to reduce sudden death and, indeed, have a variable effect on ventricular arrhythmia. Although NSVT is a marker for increased risk for sudden death, it is uncertain if antiarrhythmic drugs will prevent this outcome. Antiarrhythmic drugs have not been shown to be effective for preventing sudden death, although there are as yet no well-controlled randomized trials. Several studies suggest that amiodarone and beta blockers are beneficial, but this requires confirmation. For patients who have been resuscitated following an episode of sudden death due to a sustained ventricular tachyarrhythmia, antiarrhythmic therapy guided by invasive and noninvasive techniques appears to reduce risk of recurrent arrhythmia. However, the response rate to antiarrhythmic agents is low and side effects are common in patients with CHF. Especially important is the increased risk of precipitating CHF and aggravating the arrhythmia being treated. For many such patients who have had serious ventricular tachyarrhythmia, the automatic implantable cardioverter defibrillator may prove a better option. Other drugs used for management of CHF reduce overall mortality, but not risk of sudden death.

The relationship of the sympathetic nervous system and the renin-angiotensin system in congestive heart failure

Congestive heart failure is a complex clinical syndrome characterized by circulatory and metabolic abnormalities. It has been apparent for more than 25 years that the sympathetic nervous system and the renin-angiotensin-aldosterone system are markedly activated in the late stages of heart failure. These two systems interact to facilitate sympathetic drive and promote salt and water retention. Circumstantial evidence is now accumulating to indicate that excessive sympathetic drive and angiotensin II activity may contribute to the pathophysiology of heart failure. These observations suggest that a dual strategy of modulating sympathetic nervous system activity to the heart while blocking angiotensin II activity may provide a rational therapeutic approach to the treatment of heart failure. Xamoterol, a beta 1 partial agonist, may enhance myocardial contractile force in the steady state, while acting to inhibit excessive sympathetic drive during exercise or severe heart failure. The concomitant use of a converting-enzyme inhibitor would be expected to blunt the detrimental effects of excessive angiotensin II activity. Modulation of adrenergic drive coupled with inhibition of marked angiotensin II activity may be potentially more effective in the treatment of congestive heart failure than either strategy used alone.

The use of inotropic agents in acute and chronic congestive heart failure

This article reviews our current understanding of the physiology of myocardial contraction; recent research into its mechanical, macromolecular, and biochemical foundations; and its role in the clinical syndromes of congestive heart failure. This review serves as a background for discussing the mechanism of action and pharmacology of currently available and experimental inotropic agents. The clinical applications of these drugs are discussed and the successes and failures of the pharmacologic approach to patients with congestive heart failure analyzed.

Oral OPC-8212 for the treatment of congestive heart failure: hemodynamic improvement and increased exercise capacity

The chronic effects of the oral administration of OPC-8212 (3,4-dihydro-6-[4-(3,4-dimethoxybenzoyl)-1-piperazinyl]-2(1H)-quinolinon e) on resting hemodynamics and exercise capacity were assessed in 15 patients with congestive heart failure (NYHA II-IV). Doses of 30 or 60 mg per day were given per os over 3.0 weeks on average (range 2-6 weeks). Multigated radionuclide ventriculography and multistage exercise testing were performed before and during OPC-8212 therapy to assess the changes in left ventricular volume and exercise capacity respectively. Systolic blood pressure showed a slight increase (from 123 +/- 3 to 129 +/- 4 mmHg) during OPC-8212 therapy, while heart rate was unchanged (69 +/- 3 vs 67 +/- 3 beats/min). The left ventricular end-diastolic volume index decreased from 127 +/- 9 to 107 +/- 7 ml/m2, and ejection fraction and the P/V index (the ratio of peak systolic pressure to left ventricular end-systolic volume index) increased during OPC-8212 therapy (from 27% +/- 3% to 30% +/- 4% and from 1.5 +/- 0.2 to 2.0 +/- 0.3 mmHg/ml/m2 respectively). NYHA functional class was improved in 9 of 15 patients, and the average peak work load achieved during exercise testing increased from 27 +/- 6 to 47 +/- 7 W. No significant adverse effect was observed in any patient. These results indicate that OPC-8212 enhances the inotropic state and, hence, reduces heart size with no change in heart rate. Moreover, it increases exercise capacity. Thus, OPC-8212 is an inotropic agent with promise for application in the long-term treatment of congestive heart failure.

Pirbuterol. A preliminary review of its pharmacological properties and therapeutic efficacy in reversible bronchospastic disease

Pirbuterol is a beta-adrenoceptor agonist which differs structurally from salbutamol in the substitution of a pyridine ring for the benzene ring. In common with salbutamol, pirbuterol demonstrates both bronchodilatory and cardiovascular effects. Generally, improvements of up to 25% are noted in forced expiratory volume in 1 second (FEV1) [versus baseline or placebo] in asthmatic patients treated with pirbuterol for several months. In individual 12-week double-blind comparative studies, pirbuterol aerosol appeared similar to orciprenaline (metaproterenol) aerosol, and orally administered pirbuterol appeared similar to orally administered salbutamol in bronchodilator efficacy. However, well-designed long term comparative studies are needed to more clearly define the comparative efficacy of pirbuterol and alternative beta-adrenoceptor agonists.

Inotropic drugs and their mechanisms of action

This report describes various old and new positive inotropic drugs with respect to their mechanisms of action. Drugs with established cardiotonic effects include cardiac glycosides, beta 1-adrenergic agents, glucagon, histamine and the methylxanthines. New agents discussed are prenalterol, beta 2- and alpha-adrenergic drugs, amrinone and sulmazole. Prenalterol is a beta 1-adrenergic agent. Beta 2-adrenergic drugs, amrinone and sulmazole, combine a positive inotropic and a vasodilator effect. The latter resemble theophylline and other methylxanthines in that they appear to act mainly as phosphodiesterase inhibitors with a subsequent increase in cyclic adenosine monophosphate (cAMP). The mechanism of the positive inotropic effect of alpha-adrenergic stimulating agents (for example, phenylephrine) is unknown. It is independent of the cAMP system and is not accompanied by changes in frequency.

Pirbuterol hydrochloride: evaluation of beta adrenergic agonist activity in reversible obstructive pulmonary disease and congestive heart failure

Pirbuterol hydrochloride is a beta 2 adrenergic agonist with a structure similar to that of albuterol, except for the substitution of a pyridine ring for the benzene ring. It is comparable in duration of action to albuterol when given by inhalation, but it is threefold less potent by weight. In man, pirbuterol and albuterol have similar beta 2 selectivity. In the acute therapy of chronic obstructive pulmonary disease, pirbuterol is most effective in oral doses of 15-20 mg, and by aerosol in doses of 400 micrograms or greater. Long-term studies of oral pirbuterol in doses between 30-60 mg/day are promising, but further research is warranted. The combination of pirbuterol's beta 2 and lesser beta1 activity has proven helpful in the therapy of refractory congestive heart failure. Improvement of function of both right and left ventricles and systemic and pulmonic circulations has been demonstrated acutely. Drug effect wanes, as with other beta adrenergic agonists, due to the development of tolerance; however, long-term benefit appears to persist in both pulmonary and cardiac patients. Pirbuterol will be marketed in the United States as 10 and 15 mg tablets and as a 200 micrograms per actuation metered dose aerosol for use in pulmonary patients only; it will not be approved for use in congestive heart failure. In terms of beta 2 selectivity, duration of action, potency and frequency of side effects, pirbuterol is comparable to the two beta 2 agonists already available in the United States, albuterol and terbutaline.

Acute and long-term hemodynamic effects of oral pirbuterol in patients with chronic severe congestive heart failure: randomized double-blind trial

In 20 patients with severe congestive heart failure (CHF), we studied the effects of the beta-adrenergic agonist pirbuterol compared to placebo in both an acute double-blind randomized trial and after long-term treatment. Acutely, pirbuterol patients (n = 10) demonstrated a significant rise in cardiac index (2.2 +/- 0.14 to 3.2 +/- 0.32 L/min/m2), stroke index (26 +/- 2.6 to 35 +/- 2.9 ml/beat/m2), stroke work index (22 +/- 2.4 to 30 +/- 2.7 gm X m/m2), and ejection fraction (22 +/- 4 to 30 +/- 5%). These hemodynamic variables did not significantly change in placebo patients (n = 10). After 3 weeks of pirbuterol therapy, 14 patients (70%) were symptomatically improved and were continued on the drug for another 3 weeks; 13 of 14 patients who were symptomatically improved underwent restudy. Compared to pretreatment baseline, there was continued improvement in cardiac index (2.5 +/- 0.16 to 3.2 +/- 0.24 L/min/m2), stroke index (30 +/- 2.5 to 38 +/- 2.9 ml/beat/m2), stroke work index (26 +/- 2.3 to 35 +/- 3.1 gm X m/m2), and ejection fraction (24 +/- 1 to 28 +/- 4%). Patients more frequently improved were those with nonischemic cardiomyopathy and those with higher initial ejection fractions. These results demonstrate the acute beneficial effects of oral pirbuterol versus placebo in a double-blind randomized trial. Improvement was maintained during long-term therapy in the majority of CHF patients.

Vasodilator and inotropic therapy for severe chronic heart failure: passion and skepticism

Although substantial progress has been made in the last 5 years in the development of vasodilator and inotropic drugs for the management of patients with severe chronic heart failure, much of the enthusiasm that surrounded the introduction of many of these agents has subsequently been tempered by reports of drug failure or adverse reactions. In this review and analysis, currently available vasodilator and inotropic agents are critically and comparatively evaluated to assess their respective advantages and limitations. It is apparent that the ability of most of these drugs to produce substantial clinical benefits in patients with severe heart failure has probably been overstated. Therapy fails to achieve the desired clinical results all too frequently, possibly as the result of: the choice of an ineffective drug; the administration of an effective drug in subtherapeutic doses; the administration of an effective drug to improperly selected patients; the failure of initial hemodynamic benefits to be sustained; the occurrence of severe or serious adverse reactions; and the failure to alter concomitant therapy appropriately. The present analysis indicates that there is no uniformly effective or safe vasodilator or inotropic drug for patients with severe heart failure; all agents have important limitations. Of the available therapeutic choices, however, long-term converting enzyme inhibition appears to produce more consistent hemodynamic and clinical benefits with an acceptable degree of adverse reactions than other pharmacologic approaches for the management of these severely ill patients.

Effects of pirbuterol and sodium nitroprusside on pulmonary haemodynamics in hypoxic cor pulmonale

The acute haemodynamic effects of oral pirbuterol (a beta-agonist) were contrasted with those of sodium nitroprusside, a vasodilator, in six patients with hypoxic chronic bronchitis and emphysema. Sodium nitroprusside (1-5 mg/kg intravenously) reduced mean pulmonary arterial pressure and total pulmonary vascular resistance significantly (p less than 0.01) without change in cardiac output or right ventricular ejection fraction, measured by radionuclide ventriculography. Oral pirbuterol (22.5 mg) produced a greater reduction in total pulmonary vascular resistance than sodium nitroprusside, largely as a result of increasing cardiac output. Right ventricular ejection fraction also increased significantly after pirbuterol (p less than 0.01). Pirbuterol in a lower dosage (15 mg by mouth) in six further patients with hypoxic chronic bronchitis and emphysema produced similar changes in total pulmonary vascular resistance and right ventricular ejection fraction. Nine of the patients who were studied acutely thereafter received pirbuterol 15 mg thrice daily for six weeks, which produced a significant fall in systolic pulmonary arterial pressure and a rise in right ventricular ejection fraction (p less than 0.01), without a significant fall in arterial oxygen tension. Pirbuterol acts as a vasodilator on the pulmonary circulation in these patients and may in addition improve right ventricular performance by an inotropic action.

Effects of the beta-adrenergic receptor agonist pirbuterol on cardiac performance during acute ischaemic left ventricular failure in dogs

The effects of the beta-adrenergic receptor agonist pirbuterol on left ventricular (LV) performance were examined during acute ischaemic LV failure in anaesthetized dogs. Plastic microspheres (50 microns) were injected into the left main coronary artery, and the dogs developed severe LV failure. The stability of the heart failure model was demonstrated in a group of untreated control dogs (n = 5). Administration of pirbuterol 7 micrograms X kg-1 i.v. during failure caused an increase in cardiac output from 1.52 +/- 0.14 (mean +/- S.E.M., n = 7) to 2.56 +/- 0.32 1 X min-1 (P less than 0.01) at 30 min after drug administration. The LV end-diastolic pressure (LVEDP) decreased from 24.6 +/- 1.1 to 21.0 +/- 1.9 mmHg (P less than 0.05), and maximum LV dP/dt was increased from 2012 +/- 124 to 2602 +/- 119 mmHg X s-1 (P less than 0.01). The LVEDP-stroke work relation (n = 2) shifted markedly upward. Heart rate was not significantly changed by pirbuterol. Mean aortic blood pressure and total peripheral resistance decreased from 103 +/- 3 to 85 +/- 5 mmHg (P less than 0.05) and from 68 +/- 6 to 34 +/- 4 mmHg X 1(-1) X min (P less than 0.01), respectively. Pirbuterol increased plasma free fatty acid concentrations from 264 +/- 45 (n = 4) to a maximum value of 956 +/- 169 mumol X 1(-1). In conclusion, by a combination of inotropic stimulation and systemic vasodilation, pirbuterol markedly improved cardiac performance in dogs with acute ischaemic LV failure.

Pirbuterol, an oral beta-adrenergic receptor agonist, in the treatment of chronic cardiac failure

Pirbuterol (PB), an oral beta-adrenergic-receptor agonist, has the pharmacologic effects of vasodilation and positive inotropy. The present studies were undertaken to determine the value of PB in the long-term therapy of chronic cardiac failure. A double-blind, randomized, 7-week trial comparing PB (20 mg three times daily) with placebo in 12 patients was followed by 12 weeks of open PB therapy. Dose-dependent nervousness and tremulousness limited the unit PB dose to less than 20 mg in six patients. In all patients, clinical status, exercise tolerance and maximal oxygen uptake, left ventricular echocardiographic dimension and cardiothoracic ratio were unchanged from control after 7 weeks of placebo or PB or after 12--19 weeks of PB. To assess the adequacy of 20 mg of PB, the dose-response relations of cardiocirculatory effects to 10, 15, 20 and 30 mg of PB were compared in seven of the above patients and nine other patients. Cardiac output was significantly elevated and wedge pressure reduced after all four doses, but these changes were sustained from 6 hours after 20- and 30-mg doses only. Thus, the role of PB in the management of chronic cardiac failure appears limited; judgment of its utility must await the results of additional controlled trials.

Comparative pharmacology and clinical efficacy of newer agents in treatment of heart failure

The animal and human pharmacology of several new drugs (prazosin, trimazosin, pirbuterol, and carbazeran) useful in the treatment of congestive heart failure (CHF) is delineated in relation to the pharmacology of other agents employed for CHF management. Prazosin and trimazosin are selective alpha 1-blockers that cause a balanced increase in cardiac output (CO) and reduction in left ventricular filling pressure (LVFP); the reduction in diastolic blood pressure with these drugs is significantly related to increase in treadmill exercise, fall in LVFP, and increase in CO. Pirbuterol is a relatively selective beta 2-agonist with somewhat greater effects on CO than on LVFP. Early promise in CHF therapy is being shown by a novel series of cyclic adenosine monophosphate (cAMP) phosphodiesterase inhibitors with combined direct inotropic and vasodilator effects. Double-blind long-term studies demonstrate persistent efficacy of prazosin and trimazosin in CHF as measured by improvement in New York Heart Association functional class, treadmill exercise performance, and noninvasive measures of cardiac function; these data are supported by studies in which repeat cardiac catheterization has been performed after several months of therapy. Double-blind studies of other CHF drugs are in progress.