Inotropic drugs for the treatment of heart failure

Utility of glucagon in the emergency department

Glucagon is a pancreatic polypeptide hormone that has diverse utility as both a therapeutic and diagnostic agent. Many of its pharmacologic actions are pertinent to the practice of emergency medicine. The author reviews the literature supporting each potential use of the drug and the purported physiologic mechanisms by which glucagon exerts these actions. The indications and proper dosages for glucagon in the acute care setting are summarized.

The effect of FK664, a new cardiovascular drug, on systemic capacitance vessels in anesthetized dogs

To characterize the cardiovascular effect of FK664, a compound developed for the treatment of heart failure, the mean circulatory pressure (MCP), cardiac output and other parameters were measured in open-chest anesthetized dogs. Milrinone, a cardiotonic agent, and nifedipine, a calcium channel blocker were used as reference substances. Nifedipine (10 micrograms/kg), FK664 (0.1 mg/kg) or milrinone (0.1 mg/kg) given intravenously reduced the total peripheral resistance in a similar extent (35-40%). Whereas nifedipine had no effect on MCP, FK664 produced a significant decrease in MCP. Milrinone caused a minimal decrease in MCP, but not significantly. These results indicate that FK664 dilates the systemic capacitance vessels. This action to reduce the pre-load would be beneficial in the treatment of heart failure.

RETRACTED: Efficacy of the phosphodiesterase inhibitor enoximone in complicated cardiac surgery

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the request of the editor. In 2018, CHEST published a notice1 that all articles authored by Joachim Boldt be read with caution due to expressions of concern about falsified data. In 2020, CHEST received additional evidence of research misconduct and breaches of scientific integrity that were discovered following an investigation by the author's former institution, the University of Giessen2. In light of this new evidence, this article has been retracted by CHEST. 1. Irwin, R.S., MD, Master FCCP. Notice From the Editor in Chief. CHEST 153(3), p. 767. 2. Mukherjee, J. Statement on the scientific credibility of articles published by Joachim Boldt, formerly professor at Justus Liebig University (JLU), Giessen, Germany. https://ars.els-cdn.com/content/image/1-s2.0-S000709122030163X-mmc3.pdf.

Plasma elimination of milrinone in rats in relation to its hemodynamic effects

Milrinone (1,6-dihydro-2-methyl-6-oxo[3,4'-bipyridine]-5-carbonitrile) is a cardiotonic drug, currently under clinical investigation for the treatment of congestive heart failure. Its positive inotropic properties and its strong vasodilative action contribute to a favorable therapeutic effect. Plasma elimination of milrinone is generally by renal excretion of the unchanged drug. Since hemodynamic effects might influence the pharmacokinetics of renally eliminated drugs, we have investigated the plasma elimination of milrinone after different iv bolus doses of the compound in healthy rats. Half-times were 20.6 +/- 5.5 min (0.3 mg/kg milrinone), 17.0 +/- 1.8 min (1.0 mg/kg), 31.4 +/- 4.5 min (3.0 mg/kg), and 95.5 +/- 18.4 min (10.0 mg/kg). Clearances of milrinone showed a positive correlation with doses. Hemodynamic effects were dose dependent and (plasma) concentration dependent, and the maximum decrease in diastolic blood pressure was 54.5 +/- 0.5 mmHg. The half-effective plasma concentration of milrinone was 1.0 +/- 0.2 microM. The maximum increase in heart rate was 15%. We conclude that milrinone plasma elimination in rats is dose dependent, probably resulting from its strong vasodilator properties.

The new phosphodiesterase inhibitor enoximone in patients following cardiac surgery--pharmacokinetics and influence on parameters of coagulation

Enoximone is a selective inhibitor of the phosphodiesterase-III enzyme (PDE-III) and possesses positive inotropic and vasodilatory properties. The PDE-inhibitor amrinone has been associated with adverse effects on coagulation by decreasing platelets. To investigate the influence of enoximone on hemostasis, 18 patients undergoing elective aorto-coronary bypass grafting and receiving enoximone were compared to a control group (n = 18). In addition, the plasma levels of enoximone and its major metabolite (enoximone-sulfoxide) were studied following a single injection (0.5 mg/kg) and during a continuous infusion (5 and 10 micrograms/kg.min) before, during and after extracorporeal circulation (ECC). No difference between study and control groups was found for the parameters of coagulation during the investigation period; in particular there were no differences in platelet count and platelet function (thrombelastography). Following the single bolus, peak plasma levels decreased during ECC to ineffective levels. Continuous infusion, however, maintained effective plasma levels of enoximone; sulfoxide levels were twice as high as enoximone concentrations up until the end of the investigation period. It is concluded that enoximone can be judged to be safe in respect to its effects on coagulation even following ECC and at relatively high doses. The use of continuous infusion results in plasma levels which remain at an effective concentration through to the time that the patient is transferred to the intensive care unit.

Efficacy of enoximone in the management of refractory low-output states following cardiac surgery

Fifteen consecutive patients with post-cardiac surgery low-output states refractory to catecholamine inotropic support and intra-aortic balloon counter-pulsation (seven patients), were given enoximone (MDL 17,043, a phosphodiesterase inhibitor), 1 to 2 mg/kg, as a slow intravenous bolus injection, followed by a continuous infusion of 3 to 10 microg/kg/min. Enoximone resulted in a marked improvement in clinical and hemodynamic conditions. Despite the severity of their initial status, all the patients survived their acute circulatory failure and all but two were discharged from the hospital. Hemodynamic improvement was observed as early as 15 minutes after the drug administration and reflected the previously reported inotropic and vasodilatory properties of enoximone. No serious adverse effects were observed. Enoximone thus appears safe and effective in the management of post-cardiac surgery low-output states. Its effects are additive to those of high-dose catecholamines.

The vasorelaxant effects of milrinone and other vasodilators are attenuated by ouabain

The purpose of this study was to investigate the effect of ouabain pretreatment (1 microM) on relaxation induced by milrinone and other reference vasorelaxants in guinea pig aorta. Pretreatment with ouabain for 1 h significantly reduced the threshold concentration and increased the vasoconstrictor potency of phenylephrine. Relaxation by milrinone of aortic rings contracted by phenylephrine or by an equieffective concentration of phenylephrine in the presence of ouabain was significantly attenuated in the presence of ouabain. The effect of all other vasorelaxants tested, which included isosorbide dinitrate, hydralazine, sodium nitroprusside, forskolin, HA 1004, isoproterenol and verapamil, were also significantly reduced in the presence of ouabain. The vasorelaxant effects of milrinone and verapamil were also evaluated in K+-contracted guinea pig aorta. In contrast to results obtained with phenylephrine-contracted vessels, milrinone and verapamil were equipotent as vasorelaxants in K+-contracted vessels in the presence or absence of ouabain. The results show that ouabain not only potentiates the effect of the vasoconstrictor phenylephrine, but also reduces the potency of drugs that cause vasorelaxation in phenylephrine-contracted tissues, regardless of the mechanism of action of the vasorelaxant. These data may have clinical relevance to the concomitant use of vasodilators and digitalis in the treatment of congestive heart failure.

Comparative effects on hemodynamics of enoximone (MDL 17,043), dobutamine and nitroprusside in severe congestive heart failure

To assess their comparative effects on hemodynamics, nitroprusside, dobutamine and enoximone were sequentially administered to 10 patients with severe congestive heart failure. Nitroprusside, dobutamine (at 10 micrograms/kg/min) and enoximone (at 2 mg/kg) increased stroke volume index to a similar extent (31%, 34% and 36%, respectively). Enoximone produced less tachycardia than dobutamine and, consequently, a smaller improvement in cardiac index. Mean arterial pressure was not altered by dobutamine but was reduced 9% by enoximone, 2 mg/kg. This finding accounts for the larger (although not significant) increase in left ventricular stroke work index observed with dobutamine compared with enoximone. Ventricular filling pressures and vascular resistances were significantly decreased by all 3 drugs (p = 0.001). All 3 drugs improved cardiac pump function when assessed by the increase in stroke index to a similar extent; however, enoximone (2 mg/kg) resulted in less hypotension than nitroprusside (mean arterial pressure -9% vs -22%, p = 0.0001) and in less tachycardia than dobutamine 10 micrograms/kg/min. Those differences in mode of action account for the variations observed in the heart rate-blood pressure product (dobutamine 10 micrograms/kg/min, +18%, enoximone 2 mg/kg, -5%, p = 0.003). Enoximone thus appears to be of great value in the management of severe congestive heart failure by its combination of vasodilatory and inotropic properties. Enoximone (2 mg/kg) provides a clinically significant increase in cardiac index, a clear reduction of ventricular filling pressures, a moderate reduction of mean arterial pressure and only minor changes of heart rate and of rate pressure product.

Noninvasive delivery of a novel inotropic catecholamine: iontophoretic versus intravenous infusion in dogs

Using a newly developed iontophoretic delivery device, a novel inotropic catecholamine, pharmacologically similar to dobutamine, has been successfully administered to dogs by noninvasive transdermal infusion for periods of up to 1.5 h. The technique was compared with intravenous infusion and shown to be capable of achieving the same degree of cardiac contractility and steady-state plasma concentrations of the inotrope. There was also a good linear relationship between the applied current and the resulting steady-state plasma concentrations of the inotrope. Approximately 2 mA of applied current during transdermal iontophoresis produced a response equivalent to an intravenous infusion of 1 micrograms/kg/min of the drug.