Milrinone in the treatment of chronic cardiac failure: a controlled trial

Developments in Exercise Capacity Assessment in Heart Failure Clinical Trials and the Rationale for the Design of METEORIC-HF

Heart failure with reduced ejection fraction (HFrEF) is a highly morbid condition for which exercise intolerance is a major manifestation. However, methods to assess exercise capacity in HFrEF vary widely in clinical practice and in trials. We describe advances in exercise capacity assessment in HFrEF and a comparative analysis of how various therapies available for HFrEF impact exercise capacity. Current guideline-directed medical therapy has indirect effects on cardiac performance with minimal impact on measured functional capacity. Omecamtiv mecarbil is a novel selective cardiac myosin activator that directly increases cardiac contractility and in a phase 3 cardiovascular outcomes study significantly reduced the primary composite end point of time to first heart failure event or cardiovascular death in patients with HFrEF. The objective of the METEORIC-HF trial (Multicenter Exercise Tolerance Evaluation of Omecamtiv Mecarbil Related to Increased Contractility in Heart Failure) is to assess the effect of omecamtiv mecarbil versus placebo on multiple components of functional capacity in HFrEF. The primary end point is to test the effect of omecamtiv mecarbil compared with placebo on peak oxygen uptake as measured by cardiopulmonary exercise testing after 20 weeks of treatment. METEORIC-HF will provide state-of-the-art assessment of functional capacity by measuring ventilatory efficiency, circulatory power, ventilatory anaerobic threshold, oxygen uptake recovery kinetics, daily activity, and quality-of-life assessment. Thus, the METEORIC-HF trial will evaluate the potential impact of increased myocardial contractility with omecamtiv mecarbil on multiple important measures of functional capacity in ambulatory patients with symptomatic HFrEF. Registration: URL: https://clinicaltrials.gov; Unique identifier: NCT03759392.

Drug and Device Effects on Peak Oxygen Consumption, 6-Minute Walk Distance, and Natriuretic Peptides as Predictors of Therapeutic Effects on Mortality in Patients With Heart Failure and Reduced Ejection Fraction

Background—

Although peak oxygen consumption (peak V o 2 ), 6-minute walk distance (6MW), and natriuretic peptides (BNP and NT-proBNP) are predictors of mortality in heart failure (HF) patients, it is not known whether therapy-induced changes in these measures can predict therapeutic effect on mortality. The objective of this analysis is to quantitatively assess the relationship between therapeutic effects on commonly proposed short-term markers in HF trials and therapeutic effects on long-term outcome in patients with HF and left ventricular dysfunction.

Methods and Results—

We identified drug or device therapies for which there exists at least 1 randomized, controlled trial (RCT) assessing mortality over at least 6 months in at least 500 patients. For each of these therapies, we identified RCTs assessing the short-term changes in V o 2 , 6MW, BNP, and NT-proBNP (few of the mortality RCTs assessed the short-term changes in markers). For each intervention, we calculated the odds ratio for mortality (using random effect meta-analysis when necessary), as well as the trial level average drug- or device-induced change in the markers. We assessed the correlation between the odds ratio for death with the placebo-corrected change in the functional parameter or biomarker across the interventions. We identified mortality RCTs of 27 distinct therapies (n=73 267 patients) with a median follow-up of 19 months, that directed the search for RCTs of the effect of those interventions on the functional markers and biomarkers. There were 54 peak V o 2 trials (n=4646 patients), 34 6MW trials (n=6995 patients), 15 BNP trials (n=7233), and 6 NT-proBNP trials (n=1946) included in this analysis. There was no significant correlation between the average therapy-induced placebo-corrected change in peak V o 2 and the odds ratio for mortality ( r =0.158, P =0.26). Increased drug or device-induced average change in 6MW was correlated with increased odds ratio for mortality ( r =0.373, P =0.036). There was no significant correlation between the average therapy-induced, placebo-corrected change in the natriuretic peptides and the odds ratio for mortality (BNP: r =−0.065, P =0.82, NT-proBNP: r =−0.667, P =0.15). There was no apparent relation between change in the functional parameter or biomarker and categorical effect on mortality.

Conclusions—

This analysis, limited to trial level data from different therapeutic eras, suggests that drug- or device-induced effects on peak V o 2 , 6MW, and natriuretic peptides found in short-term trials do not predict the corresponding average long-term therapeutic effects on mortality for patients with HF and left ventricular dysfunction.

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.

Vasorelaxant effect of phosphodiesterase-inhibitor milrinone in the human radial artery used as coronary bypass graft

OBJECTIVE

The radial artery is a spastic coronary bypass graft. We investigated the effect of the phosphodiesterase III inhibitor milrinone on the human radial artery.

METHODS

Radial artery segments (n = 76) taken from 15 patients were studied in an organ chamber. Concentration-relaxation curves for milrinone were established in the radial artery precontracted with 3 vasoconstrictors (phenylephrine, K(+), and U46619). In radial artery rings incubated with therapeutic plasma concentrations of milrinone (7 and 70 micromol/L) for 10 minutes, concentration-contraction curves for the 3 vasoconstrictors were constructed.

RESULTS

Milrinone caused a submaximal relaxation in phenylephrine- (98.6% +/- 1.4%), K(+)- (89.1 +/- 4.5%), or U46619- (74.2 +/- 8.0%) precontracted radial arteries at -4.5 log(10) M. The EC(50) was higher against K(+) (-5.85 +/- 0.24 log(10) M, P =.02) or U46619 (-5. 21 +/- 0.61 log(10) M, P =.03) than phenylephrine (-6.68 +/- 0.11 log(10) M). Pretreatment with milrinone depressed the contraction by phenylephrine from 70.0% +/- 7.9% to 23.5% +/- 9.3% (P =.003) and by K(+) from 138.6% +/- 5.8% to 73.0% +/- 13.9% (P =.006) and shifted the EC(50) 3.8-fold higher (P =.03) for phenylephrine and 2.2-fold higher for K(+) (P =.01). Milrinone reduced the U46619 contraction at low concentration (-8.5 log(10) M) but had little effect on the maximal contraction.

CONCLUSION

Milrinone is a potent vasodilator for the radial artery, with possibly higher potency in alpha-adrenoceptor- and depolarizing agent K(+)-mediated, but less potency in thromboxane A(2)-mediated, contraction. Because it also has a positive inotropic effect, this vasodilator may be particularly indicated for use in patients receiving radial artery grafts in coronary artery bypass grafting.

Intermittent milrinone effect on long-term hemodynamic profile in patients with severe congestive heart failure

BACKGROUND

Many reports have suggested that intermittent milrinone infusion (IMI) may be efficacious in the management of end-stage congestive heart failure (CHF), but this issue has not been clearly established. The aim of our study was to investigate the effectiveness of IMI in hospitalized patients with severe CHF undergoing long-term (4 months) post-therapy hemodynamics.

METHODS

Thirty-six patients (28 men, 8 women; mean age 65.6 +/- 8.2 years old) with end-stage CHF (New York Heart Association functional class III-IV) were studied. Each patient received 4 cycles of 3 days per week with milrinone therapy. Each cycle consisted of a loading dose of 50 microgram/kg over 10 minutes and a 72-hour continuous infusion of 0.5 microgram/kg per minute under close monitoring. Hemodynamic changes were determined during the first and fourth cycles and on 4-month reexamination. Full clinical examination was performed at the beginning (baseline) and at the end of 4-month follow-up.

RESULTS

The values of mean pulmonary arterial pressure, pulmonary capillary wedge pressure, systemic vascular resistance, and pulmonary vascular resistance were significantly decreased (P <.01) and cardiac index was significantly increased (P <.01) compared with the baseline of first and fourth cycles. At the end of the 4-month follow-up period all hemodynamic parameters sustained the improvement. Clinical examination at the end of the 4-month period showed that 21 (58.3%) of 36 patients remained in New York Heart Association functional class IV but were hemodynamically improved, 13 (36.2%) of 36 were in functional class III, and 2 (5.5%) of 36 were in class II-III. There were no deaths during the study period.

CONCLUSIONS

Our findings suggest that IMI in hospitalized patients with severe CHF is hemodynamically efficacious. This beneficial hemodynamic effect is maintained for at least 4 months after discontinuation of therapy. These promising results raised the possibility that given appropriately, milrinone may have an important role in end-stage CHF.

Relationship between myocardial milrinone content and its acute hemodynamic and electrophysiologic effects

One of the major determinants of the short-term effects of many cardioactive drugs is the concentration of the drug specifically within the myocardium. However, no information regarding the disposition of the phosphodiesterase inhibitor milrinone in the heart is available. We therefore determined the time course of short-term myocardial milrinone uptake from paired transcoronary sampling and simultaneous coronary sinus blood flow after a 1-mg intravenous bolus in patients undergoing diagnostic cardiac catheterization. In accordance with this intention, a sensitive, reproducible method for the determination of milrinone in human whole-blood samples was developed. The reverse-phase high-performance liquid chromatographic method described used a C18 column with UV-absorbance detection at 326 nm, with a limit of detection of 0.6 ng/ml, and was highly reproducible. The short-term hemodynamic and electrophysiologic effects of the drug also were determined. Significant increases in spontaneous heart rate and LV+dP/dtmax (at constant heart rate) were observed, accompanied by reductions in mean arterial pressure, systemic vascular resistance, and PR interval, without significant changes in atrioventricular nodal or ventricular effective refractory periods. Peak content (1.89 +/- 0.30% of injected dose) was rapidly attained, 0.56 +/- 0.06 min after milrinone injection. Time of peak effects was significantly delayed (7-10 min after injection) relative to time of peak myocardial milrinone content. Residual myocardial milrinone content was 69.1 +/- 5.7% of maximum 12.5 min after injection. It is concluded that both myocardial uptake and the onset of positive inotropic effects after intravenous injection of milrinone were very rapid. However, there was significant hysteresis between peak myocardial content and subsequent hemodynamic effects.

Inhibition of vasoconstriction by phosphodiesterase III inhibitor milrinone in human conduit arteries used as coronary bypass grafts

We wished to determine the effect of phosphodiesterase III (PDE III) inhibitor milrinone on human arteries used as coronary bypass grafts. Human internal mammary artery segments (IMA, n = 109) taken from 25 patients were studied. Concentration-relaxation curves for milrinone were established in IMA precontracted with four vasoconstrictors [K+, endothelin-1 (ET-1), U46619, and phenylephrine (PE)]. In IMA rings incubated with therapeutic plasma concentrations of milrinone (7 and 70 microM) for 10 min, concentration-contraction curves for the four vasoconstrictors were constructed. Milrinone caused a complete relaxation in U46619, ET-1, PE (100%), or K+ (97.7%)-precontracted IMA. The EC50 value was higher against K+ (-5.31 +/- 0.27 log M) than PE (-6.20 +/- 0.25 log M, p = 0.036) or endothelin-1 (-6.41 +/- 0.28 log M, p = 0.018). Pretreatment with milrinone decreased the contraction induced by ET-1 from 186.0 +/- 23.3 to 66.9 +/- 9.6% (p = 0.002) and that induced by PE from 140.6 +/- 27.6 to 54.1 +/- 7.0% (p = 0.03) and shifted the EC50 7.6-fold higher (p = 0.003). Treatment of milrinone reduced the K+ and U46619 contraction (p < 0.05) at lower concentrations (between 10 and 80 mM for K+ and -8.5 and -7.5 log M for U46619) and shifted the concentration-contraction curves rightward (2.56-fold higher for K+, p < 0.0001; 3.18-fold higher for U46619, p = 0.007). Denudation of endothelium did not affect the milrinone-induced relaxation. These results demonstrate that milrinone is a potent vasodilator of human conduit arteries used as coronary bypass grafts and may have a slight selectivity with greater potency to receptor stimulants than to the depolarizing agent K+. The results may prove a particular indication for milrinone for use in patients receiving arterial grafts for coronary bypass.

Potential greater than additive vasorelaxant actions of milrinone and nitroglycerin on human conduit arteries

1. The mechanism of vasorelaxation for phosphodiesterase III inhibitors is mediated by increase of cAMP whereas for nitrovasodilators, cGMP. The purpose of this study was to test the hypothesis that the phosphodiesterase III inhibitor milrinone and nitroglycerin (NTG) may have greater than additive effects in human arteries. 2. Internal mammary artery segments (IMA, n = 90) taken from 23 patients were studied in organ chambers. The effect of milrinone (3 microM), NTG (10 nM), or the combination was tested in IMA rings precontracted with potassium (K+, 25 mM) or U46619 (10 nM). Concentration-contraction curves for K+ or U46619 were established in other rings treated with milrinone (70 microM), NTG (0.1 microM), or the combination for 10 min. 3. In K(+)-induced contraction, the combination produced more relaxation (45.4%) than did either milrinone (7.9%, P < 0.05) or NTG (3.8%, P < 0.05) alone. This relaxation was significantly more than the theoretical overadditive effect (P < 0.05). Similar results were seen in U46619-induced contraction (94.1% by the combination vs 70.7% by milrinone, P < 0.05, or 36.1% by NTG, P < 0.05). Pretreatment with the combination depressed contraction to a higher extend compared with milrinone alone (P < 0.05) for the K(+)-induced contraction and to NTG alone (P < 0.05) in U46619-induced contraction. Treatment with the combination also shifted EC50 rightward and this shift was significantly more than that caused by treatment with NTG alone (P < 0.05). 4. We conclude that there is a greater than additive vasorelaxant effect of PDE III inhibitors and nitrovasodilators in human conduit arteries. This effect may be beneficial to patients undergoing coronary artery bypass grafting and to other patients requiring these vasodilators. Reduced doses of the vasodilators in concentration may be sufficient to produce vasodilatation similar to that produced by either of them alone at higher concentrations.

Effects of a twenty-four-hour milrinone infusion in patients with severe heart failure and cardiogenic shock as a function of the hemodynamic initial condition

The systemic and pulmonary arterial hemodynamics of 40 patients with severe congestive heart failure were determined during a 24-hour infusion of milrinone (0.5 micrograms/kg/min) after a loading dose of 50 micrograms/kg. A subgroup (n = 18) with severe cardiac pump dysfunction and three patients in cardiogenic shock were analyzed separately; their hemodynamic response was compared with that of the total group (n = 40). After 15 minutes of intravenous therapy with milrinone, the total group (n = 40) showed an increase of 65% in cardiac index; in the subgroup (n = 18) cardiac index increased by 94% after 15 minutes and by 106% after 30 minutes. Likewise, pulmonary capillary wedge pressure decreased after 30 minutes in both the total group (n = 40) and the subgroup (n = 18). The heart rate showed an overall tendency to decrease. The systolic blood pressure tended upward and remained statistically unchanged in the total group, whereas in the subgroup in which pressure was initially low, there was an increase in the systolic pressure after 1 hour and a further increase after 24 hours. Mean arterial pressure also rose in this subgroup. The early improvement in all measured hemodynamic parameters was sustained throughout the 24-hour infusion period. Development of tolerance was not observed, nor were any clinically symptomatic side effects or symptomatic arrhythmias. Thus intravenous milrinone is a safe medication for the rapid and prolonged improvement in hemodynamics, specifically in patients with severely restricted cardiac pumping function.

Medical management of chronic heart failure: inotropic, vasodilator, or inodilator drugs?

On the basis of pathophysiologic mechanisms, the medical therapy of today for chronic heart failure is reviewed. The advantages and disadvantages of the vasodilator drugs and the inotropic drugs are presented. Finally, the therapeutic value of the inodilator drugs, which combine the central myocardial effects of positive inotropic agents with those of peripheral vasodilators, is discussed. In particular, the orally available dopaminergic agents, such as ibopamine, which interact with beta-receptors in the heart (mediating a positive inotropic effect) as well as with dopaminergic receptors in the peripheral vessels (mediating a systemic vasodilator effect) and in the kidneys (potentiating the natriuretic effect of diuresis), seem to be an advancement in the modern medical therapy of chronic heart failure. Data are shown during long-term treatment with ibopamine, in which the sustained clinical benefit in heart failure was not diminished, despite a decrease of the adrenergic receptors in blood cells. Dopamine plasma concentration was permanently normalized during long-term treatment. The discrepancy between clinical improvement and the measured adrenergic downregulation may be due to the interference of the inodilator with neurohormonal systems at multiple sites and is probably independent of receptor activation. It is suggested that the biosynthesis of noradrenaline is improved by increasing intracellular dopamine transport.

A comparison of oral milrinone, digoxin, and their combination in the treatment of patients with chronic heart failure

We randomly assigned 230 patients in sinus rhythm with moderately severe heart failure to treatment with digoxin, milrinone, both, or placebo. The effects of each were compared during a 12-week, double-blind trial. Treatment with milrinone or digoxin significantly increased treadmill exercise time as compared with placebo (by 82 and 64 seconds respectively; 95 percent confidence limits, 44 and 123, and 30 and 100). Both treatments reduced the frequency of decompensation from heart failure, from 47 percent with placebo to 34 percent with milrinone (P less than 0.05; 95 percent confidence limits, 22 and 46) and 15 percent with digoxin (P less than 0.01; 95 percent confidence limits, 7 and 26). However, the clinical condition of 20 percent of the patients taking milrinone deteriorated within two weeks after treatment was begun, as compared with only 3 percent of those taking digoxin (P less than 0.05). The left ventricular ejection fraction at rest was not significantly changed by milrinone (+0.2 percent; 95 percent confidence limits, -1.5 and 1.9), but it was increased by digoxin (+1.7 percent; P less than 0.01; 95 percent confidence limits, -0.03 and 3.4) and decreased by placebo (-2.0 percent; 95 percent confidence limits, -3.8 and -0.1). Three-month survival was related inversely to the base-line ejection fraction. Analysis of mortality from all causes according to the intention to treat suggested an adverse effect of milrinone (P = 0.064). After adjustment for an excess of patients with lower ejection fractions randomly assigned to receive milrinone, this trend was not significant (P = 0.26). Increased ventricular arrhythmias occurred more frequently in patients who received milrinone than in those who did not (18 vs. 4 percent; P less than 0.03). We conclude that milrinone significantly increased exercise tolerance and reduced the frequency of worsened heart failure. However, in the population of patients studied, milrinone or the combination of milrinone and digoxin offered no advantage over digoxin alone. Furthermore, our data suggest that milrinone may aggravate ventricular arrhythmias.

Controlled and uncontrolled studies of phosphodiesterase III inhibitors in contemporary cardiovascular medicine

The phosphodiesterase inhibitors are new inotrope vasodilators that have beneficial hemodynamic effects in patients with congestive heart failure (CHF). The most extensively studied agents are milrinone and enoximone. Both drugs have clearly been shown in numerous studies to improve hemodynamics in patients with CHF when given acutely by either the intravenous or oral route. In long-term studies, milrinone has been shown to have sustained beneficial hemodynamic effects during active treatment. Effects on exercise tolerance have been less clear-cut in several uncontrolled trials, but a recent large-scale randomized trial does show sustained improvement in exercise performance. When milrinone is withdrawn after long-term therapy, some studies show worsened cardiac performance; the exact cause remains ill-defined, but could be due to deterioration of baseline ventricular function or to "rebound." Both uncontrolled studies and a large recently reported randomized trial show that the hemodynamic response to readministration of milrinone after withdrawal is well-preserved, i.e., no tolerance is observed. Studies of enoximone show that its acute hemodynamic effects are similar to those of milrinone, but its long-term efficacy, using both hemodynamic and exercise end points, is less clear-cut, and no large-scale randomized trials of enoximone therapy have yet been reported. The studies of both these agents performed thus far indicate that the phosphodiesterase inhibitors have considerable promise for both acute and long-term treatment of patients with CHF.

Effect of phosphodiesterase inhibitors on survival of patients with chronic congestive heart failure

Controlled and uncontrolled hemodynamic and clinical studies have noted that the long-term treatment of patients with chronic heart failure with phosphodiesterase (PDE) inhibitors, such as amrinone, milrinone, enoximone and imazodan, may accelerate progression of the underlying disease and provoke serious ventricular arrhythmias. However, in an experimental model of chronic progressive left ventricular dysfunction, milrinone has been reported to reduce mortality to a degree comparable to that seen with the converting-enzyme inhibitors. These discordant observations suggest that either the deleterious hemodynamic and electrophysiologic effects of the PDE inhibitors are not translated into an adverse effect on mortality, or the animal model used to evaluate the effects of milrinone cannot be used to investigate the action of these drugs in human heart failure. Unfortunately, no trial has prospectively evaluated the effect of PDE inhibition on the survival of patients with heart failure. To address this need, the Prospective Randomized Milrinone Survival Evaluation (PROMISE Trial) has been launched in 75 to 90 clinical research centers in the United States and Canada. This study will enroll 750 patients with severe (class IV) heart failure, who have symptoms refractory to conventional therapy with digitalis, diuretics, converting-enzyme inhibitor and direct-acting vasodilators. Patients will be randomly assigned to additional treatment with either oral milrinone or placebo, and followed until death or to the conclusion of the study. The primary end point will be all-cause mortality, but the effect of milrinone on functional capacity will also be evaluated. The results of the study should define the place of PDE inhibitors in the treatment of chronic heart failure.

Vasodilator and inotropic drugs for the treatment of chronic heart failure: distinguishing hype from hope

During the past 10 years, more than 80 orally active vasodilator and inotropic agents have been tested in the clinical setting to evaluate their potential utility in the treatment of chronic heart failure. Although the initial reports of all of these drugs suggested that each represented a major therapeutic advance, only three agents--digoxin, captopril and enalapril--have produced consistent long-term hemodynamic and clinical benefits in these severely ill patients. Most of the other drugs that have been tested have not (to date) distinguished themselves from placebo therapy in large-scale, controlled trials, even though these agents produce hemodynamic effects that closely resemble those seen with digitalis and the converting-enzyme inhibitors. These observations suggest that the hemodynamic derangements that characteristically accompany the development of left ventricular dysfunction cannot be considered to be the most important pathophysiologic abnormality in chronic heart failure. Although cardiac contractility is usually depressed in this disease, positive inotropic agents do not consistently improve the clinical status of these patients. Similarly, although the systemic vessels are usually markedly constricted, drugs that ameliorate this vasoconstriction do not consistently relieve symptoms, enhance exercise capacity or prolong life. Hence, correction of the central hemodynamic abnormalities seen in heart failure may not necessarily provide a rational basis for drug development, and future advances in therapy are likely to evolve only by attempting to understand and modify the basic physiologic derangements in this disorder.

The pharmacokinetics and pharmacodynamics of newer inotropic agents

In the past few years an intense effort has been directed toward the development of new inotropic agents for the treatment of chronic cardiac failure. Traditionally, therapy of this disease has included treatment with digitalis glycosides, diuretics, sodium restriction and vasodilators. While digitalis has proven to be an effective inotropic agent, it possesses a low therapeutic index and many patients remain symptomatic or 'refractory' despite its inotropic effects. This review focuses on the pharmacokinetics and pharmacodynamics of newer inotropic agents that have been developed or which are currently undergoing investigation. Amrinone and milrinone are two bipyridine derivatives which have been shown to be effective in the short term treatment of cardiac failure. Milrinone is currently being evaluated for its long term efficacy. The mechanism of action of amrinone and milrinone appears to be unrelated to the cardiac glycosides and sympathomimetic agents, and they are rapidly and well absorbed following oral administration. The bioavailability of milrinone appears to be somewhat reduced in patients with chronic cardiac failure. The distribution of these drugs to extravascular tissues is very rapid; the volume of distribution suggests that they are not extensively bound to tissues. While the volume of distribution of amrinone appears to be unaffected by the presence of heart failure, that of milrinone appears to be somewhat enhanced. The major route of elimination of both drugs appears to be excretion into urine as unchanged drug. A substantial fraction of the amrinone dose, however, undergoes hepatic metabolism to many metabolites, including an N-acetyl derivative. Clearance of amrinone and milrinone is dramatically reduced in patients with chronic cardiac failure compared with normal volunteers, resulting in proportionate increases in the serum half-lives of these drugs. Studies examining the acute and chronic disposition of these agents in cardiac failure patients have not demonstrated changes in their pharmacokinetics secondary to improvements in cardiocirculatory function. Both drugs show strong correlations between mean improvements in haemodynamics and drug serum concentrations, although considerable intrapatient variability may exist. It is currently unclear as to whether the site for the pharmacological action of amrinone is pharmacokinetically distinguishable from plasma. Enoximone and its sulphoxide metabolite, piroximone, are two compounds currently undergoing investigation for the treatment of chronic cardiac failure.(ABSTRACT TRUNCATED AT 400 WORDS)

Newer positive inotropic agents in the treatment of chronic cardiac failure. Current status and future directions

Heart failure is a serious worldwide health problem of major proportions. For many physicians, digitalis (an inotropic agent of limited proportions) and diuretics have proven the standard of treatment for heart failure. Vasodilators have also gained acceptance in recent years. Nevertheless, many patients remain symptomatic and therefore attention has been given to the development of pharmacological agents with mechanisms of action targeted to cardiac and vascular smooth muscle. The newer generation of inotropic agents have clearly been shown to improve the pumping function of the failing heart in patients who remain symptomatic despite digitalis, diuretics and vasodilators, while myocardial oxygen consumption is not enhanced. Several uncontrolled trials with the phosphodiesterase inhibitors enoximone, milrinone and piroximone have concluded that these agents improve exercise capacity and thereby hold promise to enhance quality of life. Large scale controlled trials currently in progress will determine the ultimate efficacy, as well as safety, of these agents. Results to date with several orally active beta-adrenoceptor agonists suggest that their efficacy may be limited by the induction of ventricular arrhythmias.