Central and regional hemodynamic effects of oral enoximone in congestive heart failure: a double-blind, placebo-controlled study

Rationale and design of the enoximone clinical trials program

BACKGROUND

Chronic heart failure is a disease syndrome characterized in its advanced stages by a poor quality of life, frequent hospitalizations, and a high risk of mortality. In advanced and ultra-advanced chronic heart failure, many treatment options, such as cardiac transplantation and mechanical devices, are severely limited by availability and cost. Short-term Phase II clinical trials suggest that low-dose oral inotropic therapy with enoximone may improve hemodynamics and exercise capacity, without adversely affecting mortality, in selected subjects with advanced chronic heart failure. Based on these data, the ability of enoximone to deliver safe and efficacious palliative treatment of advanced/ultra-advanced chronic heart failure is being evaluated in Phase III clinical trials.

METHODS AND RESULTS

The Enoximone Clinical Trials Program is a series of 4 clinical trials designed to evaluate the safety and efficacy of oral enoximone in advanced chronic heart failure. ESSENTIAL I and II (The Studies of Oral Enoximone Therapy in Advanced Heart Failure) will investigate the effects of oral enoximone on all-cause mortality and cardiovascular hospitalization, submaximal exercise capacity, and quality of life in subjects with New York Heart Association Class III/IV chronic heart failure. EMOTE (Oral Enoximone in Intravenous Inotrope-Dependent Subjects) will evaluate the potential of oral enoximone to wean subjects with ultra-advanced chronic heart failure from chronic intravenous inotropic therapy to which they have been shown to be dependent. EMPOWER (Enoximone Plus Extended-Release Metoprolol Succinate in Subjects with Advanced Chronic Heart Failure) will explore the potential of enoximone to increase the tolerability of continuous release metoprolol in subjects shown previously to be hemodynamically intolerant to beta-blocker treatment.

CONCLUSION

These studies are Phase III, multicenter, randomized, double-blinded, placebo-controlled trials designed to test the general hypothesis that chronic oral administration of low doses of enoximone can produce beneficial effects in subjects with advanced or ultra-advanced chronic heart failure.

Phosphodiesterase III inhibitors for heart failure

BACKGROUND

In the treatment of chronic heart failure, vasodilating agents, ACE inhibitors and beta-blockers have shown an increase of life expectancy. Another strategy is to increase the inotropic state of the myocardium : phosphodiesterase inhibitors (PDIs) act by increasing intra-cellular cyclic AMP, thereby increasing the concentration of intracellular calcium, and lead to a positive inotropic effect.

OBJECTIVES

This overview on summarised data aims to review the data from all randomised controlled trials of PDIs III versus placebo in symptomatic patients with chronic heart failure. The primary endpoint is total mortality. Secondary endpoints are considered such as cause-specific mortality, worsening of heart failure (requiring intervention), myocardial infarction, arrhythmias and vertigos. We also examine whether the therapeutic effect is consistent in the subgroups based on the use of concomitant vasodilators, the severity of heart failure, and the type of PDI derivative and/or molecule. This overview updates our previous meta-analysis published in 1994.

SEARCH STRATEGY

Randomised trials of PDIs versus placebo in heart failure were searched using MEDLINE (1966 to 2004 January), EMBASE (1980 to 2003 December), Cochrane CENTRAL trials (The Cochrane Library Issue 1, 2004) and McMaster CVD trials registries, and through an exhaustive handsearching of international abstracting publications (abstracts published in the last 22 years in the "European Heart Journal", the "Journal of the American College of Cardiology" and "Circulation").

SELECTION CRITERIA

All randomised controlled trials of PDIs versus placebo with a follow-up duration of more than three months.

DATA COLLECTION AND ANALYSIS

21 trials (8408 patients) were eligible for inclusion in the review. 4 specific PDI derivatives and 8 molecules of PDIs have been considered.

MAIN RESULTS

As compared with placebo, treatment with PDIs was found to be associated with a significant 17% increased mortality rate (The relative risk was 1.17 (95% confidence interval 1.06 to 1.30; p<0.001). In addition, PDIs significantly increase cardiac death, sudden death, arrhythmias and vertigos. Considering mortality from all causes, the deleterious effect of PDIs appears homogeneous whatever the concomitant use (or non-use) of vasodilating agents, the severity of heart failure, the derivative or the molecule of PDI used.

AUTHORS' CONCLUSIONS

Our results confirm that PDIs are responsible for an increase in mortality rate compared with placebo in patients suffering from chronic heart failure. Currently available results do not support the hypothesis that the increased mortality rate is due to additional vasodilator treatment. Consequently, the chronic use of PDIs should be avoided in heart failure patients.

Low-dose enoximone improves exercise capacity in chronic heart failure. Enoximone Study Group

OBJECTIVES

This study was designed to evaluate the effects of low-dose enoximone on exercise capacity.

BACKGROUND

At higher doses the phosphodiesterase inhibitor, enoximone, has been shown to increase exercise capacity and decrease symptoms in heart failure patients but also to increase mortality. The effects of lower doses of enoximone on exercise capacity and adverse events have not been evaluated.

METHODS

This is a prospective, double-blind, placebo-controlled, multicenter trial (nine U.S. centers) conducted in 105 patients with New York Heart Association class II to III, ischemic or nonischemic chronic heart failure (CHF). Patients were randomized to placebo or enoximone at 25 or 50 mg orally three times a day. Treadmill maximal exercise testing was done at baseline and after 4, 8 and 12 weeks of treatment, using a modified Naughton protocol. Patients were also evaluated for changes in quality of life and for increased arrhythmias by Holter monitoring.

RESULTS

By the protocol-specified method of statistical analysis (the last observation carried-forward method), enoximone at 50 mg three times a day improved exercise capacity by 117 s at 12 weeks (p = 0.003). Enoximone at 25 mg three times a day also improved exercise capacity at 12 weeks by 115 s (p = 0.013). No increases in ventricular arrhythmias were noted. There were four deaths in the placebo group and 2 and 0 deaths in the enoximone 25 mg three times a day and enoximone 50 mg three times a day groups, respectively. Effects on degree of dyspnea and patient and physician assessments of clinical status favored the enoximone groups.

CONCLUSIONS

Twelve weeks of treatment with low-dose enoximone improves exercise capacity in patients with CHF, without increasing adverse events.

Effect of enoximone alone and in combination with metoprolol on myocardial function and energetics in severe congestive heart failure: improvement in hemodynamic and metabolic profile

The hemodynamic and myocardial metabolic effects of enoximone (phosphodiesterase III inhibitor), alone or in combination with metoprolol (beta-adrenergic blocker), were studied in patients with congestive heart failure. Ten patients (New York Heart Association Class III-IV) underwent right heart and coronary sinus catheterization, and parameters were assessed at basal condition, at peak enoximone response (mean intravenous loading dose = 2.2 mg/kg), and after the combination with metoprolol (mean intravenous dose = 8.5 mg). Heart rate tended to increase during enoximone administration (from 102 +/- 16 to 107 +/- 16 min-1, ns) and was reduced during enoximone plus metoprolol (to 88 +/- 15 min-1, p < 0.05 vs. basal). Cardiac index was increased during enoximone (from 2.2 +/- 0.2 to 3.8 +/- 0.5 1/min/m2, p < 0.05) and decreased during enoximone plus metoprolol (to 2.8 +/- 0.5 1/min/m2, p < 0.05 vs. enoximone). Mean pulmonary wedge pressure fell during enoximone and remained reduced during enoximone plus metoprolol (from 27 +/- 9 to 9 +/- 3 and to 13 +/- 4 mmHg, respectively, both p < 0.05). Myocardial oxygen consumption did not change during enoximone (from 27 +/- 8 to 25 +/- 13 ml/min, ns) and was reduced during enoximone plus metoprolol (to 19 +/- 8 ml/min, p < 0.05 vs. basal). Myocardial lactate extraction tended to be lower during enoximone and during enoximone plus metoprolol conditions (from 38 +/- 17% to 26 +/- 20% and to 29 +/- 24%, respectively), but no statistical significance was found. Myocardial efficiency was increased during enoximone and during enoximone plus metoprolol (from 9 +/- 3% to 15 +/- 6% and to 14 +/- 6%, respectively, both p < 0.05). Thus in patients with congestive heart failure enoximone improves hemodynamics and, in most cases, it does not influence energetics. The addition of metoprolol to enoximone reduces heart rate, cardiac index, and myocardial oxygen consumption without any other major changes, producing a more physiologic hemodynamic and metabolic profile.

Arterial hemodynamics and cardiac effects of enoximone, dobutamine, and their combination in severe heart failure

The acute systemic and regional hemodynamic effects of dobutamine (5, 10, and 15 micrograms/kg/min intravenously), of enoximone (1, 1.5, and 2 mg/kg intravenously), and of the dobutamine-enoximone combination were compared in eight patients with severe congestive heart failure. Dobutamine and enoximone similarly and dose-dependently increased cardiac index and decreased systemic vascular resistance, right atrial pressure, and mean capillary wedge pressure. Dobutamine, but not enoximone, increased heart rate after 10 and 15 micrograms/kg/min. The combination of the two drugs caused a greater increase in cardiac index and a greater decrease in total peripheral resistance than did each drug alone. In the forearm vascular bed, brachial blood flow and brachial artery diameter were increased by enoximone significantly and dose-dependently and by dobutamine only at 5 micrograms/kg/min. Finally, the combination of the two drugs increased brachial blood flow but not brachial artery diameter to a larger extent than enoximone alone. Hepatosplanchnic and renal blood flows were not altered by any of the treatments. These results indicate that (1) enoximone exerts a significantly greater muscular vasodilator action than dobutamine; (2) the dobutamine-enoximone combination potentiates the systemic and brachial vasodilator effects of each drug; and (3) high doses of dobutamine (10 and 15 micrograms/kg/min) improve hemodynamics through their positive inotropic and chronotropic effects, whereas at low doses (5 micrograms/kg/min) a peripheral vasodilation also contributes.

Regional blood flow in human congestive heart failure

Despite the total-body consequences of congestive heart failure, little information is available on the distribution of cardiac output and regional-organ hemodynamics in this condition in humans. Technical and methodologic limitations probably account for the paucity of data in this area. Available data indicate that blood flow to the regions or organs studied, namely, the kidneys, hepatosplanchnic region, and upper limbs, decreases in proportion to the reduction in cardiac output. However, renal blood flow appears to be protected in human heart failure by a form of "autoregulation" during marked depression of cardiac output (less than 2.0 L/min/m2). Results of preliminary studies suggest that the regulation of regional-organ hemodynamics is disturbed in this human condition. Cardioactive drugs profoundly affect regional-organ hemodynamics independent of changes in central hemodynamics and cardiac output. The determination of regional blood flow responses in human heart failure will become more important as we expand our knowledge base of the pathophysiology of heart failure, learn more about local vascular control mechanisms, and pursue the potential therapeutic objective of selectively augmenting regional-organ hemodynamics and function.

Current status of non-digitalis positive inotropic drugs

Considerable effort and resources have been directed at the development and study of positive inotropic drugs over the past 10-15 years. Much has been learned about the physiology and pharmacology of myocardial contraction, the application of agents to augment contractility, and, importantly, the general and specific limitations of positive inotropic therapy. Studies on acute inotropic intervention have now shown that a drug's ability to augment overall cardiac performance is heavily dependent on its effects on vasculature, vascular control, and ventricular-vascular coupling. The clinical research on new agents has served to remind us how difficult it is to formulate the "ideal" positive inotropic or cardiovascular support drug for the critical care setting. The vast effort to develop a chronically and orally administrable drug to replace or even supplement digitalis has generally been disappointing. The dopaminergic agents (e.g., ibopamine, levodopa) act primarily via vasodilation and their effectiveness and role in managing heart failure remain unresolved. The initial excitement about the phosphodiesterase III inhibitors (e.g., amrinone, milrinone, enoximone) has been tempered by the results of large well-designed trials indicating variable effectiveness and a prominent adverse effect profile. During long-term oral administration none of these agents has been shown to improve clinical status or exercise capacity beyond that achieved by digoxin, when administered either separately or in combination with digoxin. The Prospective Randomized Milrinone Survival Evaluation (PROMISE) trial, showing that repeated oral administration of milrinone can increase mortality in heart failure, is having a devastating effect on the further development of this class of drugs.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic and neuroendocrine response to acute administration of the phosphodiesterase inhibitor BM14.478 in patients with congestive heart failure

The benzimidazol analogue BM14.478 is a phosphodiesterase inhibitor with both vasodilator and positive inotropic properties. Hemodynamic parameters and plasma hormone levels of 8 patients (1 female, 7 male) with chronic congestive heart failure NYHA Classes II-IV (1 patient with coronary artery disease, 7 patients with primary dilated cardiomyopathy) were assessed before and until 6 h after the intravenous application of 1.0 mg BM14.478. There was a significant decrease of mean pulmonary artery pressure (28 +/- 11 vs. 23 +/- 11 mmHg; p less than 0.05), mean right atrial pressure (8.6 +/- 5.2 vs. 5.0 +/- 4.7 mmHg; p less than 0.02), and systemic vascular resistance (1651 +/- 484 vs. 1206 +/- 252 dynes.s.cm-5; p less than 0.05) as early as 10 min after injection of BM14.478. Pulmonary vascular resistance also was reduced (128 +/- 86 vs. 61 +/- 39 dynes.s.cm-5, 30 min after injection; p less than 0.02). Simultaneously there was a significant increase of cardiac index (2.3 +/- 0.7 vs. 3.1 +/- 0.8 l.min-1.m-2, 10 min after injection; p less than 0.02), and stroke volume index (28.8 +/- 11.7 vs. 33.9 +/- 8.5 ml.min-1.m-2; 30 min after injection; p less than 0.05). Although mean heart rate did not change significantly, some patients reacted with a transient increase. There was also a slight but insignificant increase of the double product. No serious side effects were observed. The hemodynamic improvement was followed by a delayed reduction of plasma levels of epinephrine (51 +/- 20 vs. 41 +/- 21 pg/ml; p less than 0.02; 30 min after injection) and atrial natriuretic peptide (229 +/- 283 vs. 121 +/- 168 pg/ml; p less than 0.05; 1 h after injection). Mean levels of plasma norepinephrine, however, did not change significantly and individual responses showed large variations, which could not be predicted by the behavior of the hemodynamic parameters. Three of eight patients (2 of these with elevated baseline filling pressures) even showed a marked increase of plasma norepinephrine levels after BM14.478. Response of plasma renin activity and plasma vasopressin levels to BM14.478 also was heterogeneous. According to the results of this study, acute administration of the phosphodiesterase inhibitor BM14.478 has an immediate beneficial hemodynamic effect in patients with severe congestive heart failure by reducing both preload and afterload, and by increasing cardiac index and stroke volume. However, this improvement of hemodynamic parameters is not necessarily accompanied by a favorable short-term response of plasma hormones, and therefore does not allow any conclusions on survival of these patients.

Oral enoximone therapy in chronic heart failure: a placebo-controlled randomized trial. The Western Enoximone Study Group

In a parallel study design, 164 patients with New York Heart Association Functional class II or III heart failure were randomized to receive either enoximone given as 50 mg three times a day, or 100 mg three times a day, or a matching placebo. All patients were receiving digitalis and/or diuretics and had left ventricular ejection fractions less than or equal to 45. Exercise tests were performed after 1, 4, 8, and 12 weeks of treatment. Enoximone produced significantly greater increases in exercise time than placebo treatment at weeks 4 and 8 (p = 0.012, p = 0.029, respectively) but not after 12 weeks. Left ventricular ejection fraction increased significantly after the first dose of enoximone but not after 12 weeks of long-term therapy. Heart failure symptoms and the physicians' evaluations of cardiac status were significantly improved in both enoximone therapy groups during the first 4 weeks of evaluation when compared with evaluations of cardiac status in the placebo group. Diuretic doses were increased more frequently for patients who were receiving a placebo. Adverse events were reported with similar frequency in the placebo and 50 mg enoximone treatment groups; 100 mg enoximone resulted in a significantly greater incidence of adverse events. Mean heart rate and ventricular ectopic activity were not significantly different among the three treatment limbs. Enoximone appears to improve exercise tolerance, ventricular function, and symptoms of heart failure for 4 to 8 weeks. Heart rate, ventricular ectopic activity, and mortality rate were not increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Multicenter trial of oral enoximone in patients with moderate to moderately severe congestive heart failure. Lack of benefit compared with placebo. Enoximone Multicenter Trial Group

A multicenter double-blind, randomized, placebo-controlled trial of oral enoximone, a phosphodiesterase inhibitor, was conducted in 102 outpatients (50 receiving enoximone and 52 receiving placebo) with moderate to moderately severe congestive heart failure. All were on a long-term regimen of digoxin and diuretics without vasodilators and converting enzyme inhibitors. Symptom score was obtained, and exercise testing was performed monthly for 4 months. There were no differences between groups in symptoms or exercise duration at the end of 4 months. A subgroup undergoing analysis of oxygen consumption with measurement of anaerobic threshold during exercise showed an increase (p less than 0.05) in anaerobic threshold at 1 month with enoximone. (2.7 +/- 0.8 ml O2/kg/min) compared with placebo (-0.8 +/- 1.2 ml O2/kg/min). This improvement was not sustained at 4 months (0.5 +/- 1.7 ml O2/kg/min with enoximone and 0.2 +/- 1.5 ml O2/kg/min with placebo). The dropout rate was significantly higher (p less than 0.02) with enoximone (46%) than with placebo (25%). Adverse effects other than death were slightly, but not significantly, higher with enoximone (32%) than with placebo (22%). During therapy, five deaths occurred in the enoximone group, and none occurred in the placebo group (p less than 0.05). Two deaths were sudden, two were from progressive congestive heart failure, and one was from acute myocardial infarction. With intention-to-treat analysis and inclusion of patients who were removed from therapy because of lack of study drug effect, 10 deaths occurred in the enoximone group, and three occurred in the placebo group (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Placebo-controlled trial of oral enoximone in end-stage congestive heart failure refractory to optimal treatment

A double-blind, randomized, concurrent trial of enoximone vs placebo was undertaken to assess the efficacy and safety of enoximone, 100 mg t.d.s. added to optimal therapy in 30 patients (mean age, 66.4 +/- 14 years) with severe congestive heart failure. Before inclusion, all patients remained markedly symptomatic despite treatment with diuretics, digitalis, vasodilators and angiotensin converting enzyme inhibitors. Symptoms and quality of life were evaluated at inclusion, and at days 4 and 31; 24-hour electrocardiography and Doppler echocardiography were performed at inclusion and at day 31. Clinical and echocardiographic baseline characteristics were similar in the two groups. During the study, 10 patients dropped out: 3 in the enoximone group (1 death) and 7 in the placebo group (3 deaths). At day 4, symptoms were improved in 13 enoximone-treated patients and in 8 patients on placebo (P less than 0.05). At day 31, symptoms were still improving in 10 of 12 patients on enoximone and in 6 of 8 patients on placebo (NS). No serious clinical side-effects were reported, and no statistically significant difference in the frequency of premature ventricular contractions between the two groups was apparent on Holter monitoring. Peak acceleration of ascending aortic blood flow at entry was 17 +/- 6 m/second2 in the enoximone group and 18 +/- 5 m/second2 in the placebo group (NS). At day 31, the change in peak acceleration was +20% in the enoximone group vs -6% in the placebo group (P less than 0.05). Cardiac index increased by 18% in the enoximone group (from 2.17 +/- 0.7 litres/minute/m2 to 2.4 +/- 1.0 litres/minute/m2 (NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphodiesterase inhibition by new cardiotonic agents: mechanism of action and possible clinical relevance in the therapy of congestive heart failure

Cyclic AMP is known as a secondary messenger regulating the myocardial force of contraction. For the degradation of cAMP multiple forms of PDE within the cell are described, which vary according to substrate specificity, kinetic characterization, and cellular localization. One of these isoenzymes, the low Km cAMP-specific PDE (PDE III), which seems to be closely related to cardiotonic effects of PDE inhibitors, exists either in a particulate form (in dogs), probably associated with the sarcoplasmic reticulum, or in soluble form (in guinea pig). The existence of different forms of PDE III possibly reflects a different pooling or compartmentalization of cAMP. Many agents selectively inhibiting PDE III are described which potently increase the force of contraction and which exert vasodilatory effects. Besides PDE inhibition some of these agents possess additional cAMP-independent actions, e.g., sensitization of the contractile proteins to Ca2+, prolongation of the action potential, or prolongation of the open state of the Na+-channel. Since agents which nonselectively inhibit PDE are known as potent positive inotropic agents (e.g., IBMX), PDE III inhibition itself, but not a selectivity for PDE III inhibition, seems to be a prerequisite for this mechanism of action of cardiotonic drugs. Investigations with preparations from diseased human myocardium show that the beta-adrenoceptor agonist isoprenaline as well as the PDE inhibitor IBMX increase the force of contraction to only about one-third of the maximal effect of the cardiac glycoside dihydro-ouabain or Ca2+. In nonfailing human heart preparations all agents had equal activity. Possible reasons for these differences may be a decreased responsiveness to beta-adrenoceptor stimulation (beta-receptor down-regulation) or an inappropriate increase in cAMP levels due to increased activity of inhibitory Gi-proteins with resulting decrease of adenylate cyclase activity in the failing heart. Besides a short-term clinical and hemodynamic improvement of congestive heart failure, uncontrolled long-term administration of PDE III-inhibitor agents failed to produce sustained clinical benefit and had no effect on survival. Controlled long-term studies with new cardiotonic agents in patients with severe CHF are still lacking.

Disparity between improvement in left ventricular function and changes in clinical status and exercise capacity during chronic enoximone therapy

Twenty patients with moderately severe congestive heart failure were randomized to chronic enoximone (n = 10) or placebo (n = 10) therapy in a double-blind manner and serially evaluated over a 16-week-period. The purpose of the study was to determine if the addition of standard doses (1 and 2 mg/kg) of this new phosphodiesterase inhibitor to conventional therapy (digitalis and diuretics) would alter the clinical and laboratory course of this patient population. Except for a transient improvement in the quality of life score, none of the symptomatology indicators were significantly affected by enoximone. Similarly, maximal exercise capacity was not altered. Enoximone did elicit a statistically significant augmentation of echocardiographic, radionuclide angiographic, and systolic time interval parameters of left ventricular function. These enoximone-induced effects were accompanied by a significant increase (7% to 11%) in resting heart rate. Enoximone is capable of improving ventricular function when added to digitalis-diuretic therapy in moderately severe congestive heart failure. While individual patients may benefit from enoximone, the ability of standard doses of this agent to improve symptoms and exercise capacity over a 16-week period appears somewhat limited in a moderately severe heart failure population as a whole. Furthermore, a disparity between improvement in ventricular function parameters and changes in clinical status and exercise performance is apparent in this heart failure population.

Regional blood flow responses to vasodilators and inotropes in congestive heart failure

Regional blood flow and the distribution of cardiac output is an important aspect of the pathophysiology and pharmacology of human congestive heart failure. This study presents the cumulative experience and data from our laboratories with specific reference to (1) the regional blood flow responses, some rather unique, to various vasodilators and inotropes in patients with congestive heart failure (CHF), and (2) the pharmacophysiologic conclusions and concepts that have evolved from these data. Certain drugs and drug groups evoke rather consistent changes in the blood flow of certain organ systems in CHF. Renal blood flow is augmented by hydralazine, an effect that persists with chronic administration. The converting enzyme inhibitors, captopril and enalapril, increase renal blood flow; this implies that the renin-angiotensin II-aldosterone axis plays a major role in modifying renal blood flow and regional blood flow distribution in human CHF. Nitrates either reduce or do not change renal blood flow. Augmentation of hepatic-splanchnic blood flow occurs after first-dose alpha 1-adrenoceptor blockade suggesting that alpha-adrenergic agonism plays an important role in modifying hepatic-splanchnic flow and the regional distribution of cardiac output in CHF. A number of drugs and drug groups increase limb blood flow (e.g., dobutamine, dopexamine, intravenous nitrates, nitroprusside, hydralazine and nifedipine). With respect to regional blood flow and the distribution of cardiac output in CHF, major differences have been shown to exist between drug groups, between drugs within a group and between different doses of a drug. Certain agents can cause a redistribution of systemic flow without changing cardiac output.(ABSTRACT TRUNCATED AT 250 WORDS)