Differential inotropic effects of flosequinan in ventricular muscle from normal ferrets versus patients with end-stage heart failure

Consequences of Discontinuing Long-Term Drug Treatment in Patients With Heart Failure and Reduced Ejection Fraction

There is uncertainty regarding the clinical effects of discontinuation of drugs for heart failure after long-term use. The withdrawal of long-term treatment can follow 1 of 4 distinct patterns: 1) loss of on-treatment effect with no observed changes following discontinuation (eg, prazosin); 2) attenuation or loss of on-treatment effect with rebound clinical worsening following discontinuation (eg, nitroprusside); 3) persistence of deleterious on-treatment effect followed by clinical worsening after discontinuation (eg, milrinone and flosequinan); and 4) persistence of favorable on-treatment effect followed by clinical worsening after discontinuation (eg, digoxin and sodium-glucose cotransporter 2 inhibitors). Persuasive evidence for persistence of efficacy has been demonstrated for the use of digoxin, diuretic agents, sodium-glucose cotransporter 2 inhibitors, and (to a limited extent) for angiotensin-converting enzyme inhibitors. Available evidence for worsening of clinical status following the withdrawal of neurohormonal antagonists largely consists of observational studies. However, their findings are difficult to interpret because of considerable confounding related to the fact that drugs were withdrawn for clinical reasons, which represented a more important contributor to the poor outcome of these patients than the withdrawal of an effective drug. Nevertheless, the totality of available evidence points to a meaningful clinical deterioration within a few weeks following the withdrawal for most drugs that have been evaluated for the treatment of heart failure. These findings suggests that that our current emphasis on the implementation of foundational drugs needs to include an equally important emphasis to avoid even short-term gaps in treatment.

Long-Term Effects of Flosequinan on the Morbidity and Mortality of Patients With Severe Chronic Heart Failure: Primary Results of the PROFILE Trial After 24 Years

OBJECTIVES

The purpose of this clinical trial was to evaluate the long-term effects of flosequinan on the morbidity and mortality of patients with severe chronic heart failure.

BACKGROUND

Flosequinan was the first oral vasodilator to be used in the clinic to augment the effects of digitalis, diuretics, and angiotensin-converting enzyme inhibitors in heart failure. However, the drug activated neurohormonal systems and exerted both positive inotropic and chronotropic effects, raising concerns about its safety during long-term use.

METHODS

Following a run-in period designed to minimize the risk of tachycardia, we randomly assigned 2,354 patients in New York Heart Association functional class III to IV heart failure and with an ejection fraction ≤35% to receive long-term treatment with placebo or flosequinan (75 or 100 mg/day) in addition to their usual therapy. The primary outcome was all-cause mortality.

RESULTS

The trial was terminated after a recommendation of the Data and Safety Monitoring Board, because during an average of 10 months of follow-up, 192 patients died in the placebo group and 255 patients died in the flosequinan group (hazard ratio: 1.39, 95% confidence interval: 1.15 to 1.67; p = 0.0006). Flosequinan also increased the risk of disease progression, which was paralleled by drug-related increases in heart rate and neurohormonal activation. However, during the first month, patients in the flosequinan group were more likely to report an improvement in well-being and less likely to experience worsening heart failure. Similarly, during the month following drug withdrawal at the end of the trial, patients withdrawn from flosequinan were more likely than those withdrawn from placebo to report symptoms of or to require treatment for worsening heart failure.

CONCLUSIONS

Although flosequinan produced meaningful symptomatic benefits during short- and long-term treatment, the drug increased the risk of death in patients with severe chronic heart failure.

Mechanisms of positive inotropic action of flosequinan, hydralazine, and milrinone on mammalian myocardium

Flosequinan is an arterial and venous dilator that also has a positive inotropic effect at relatively higher doses. The purpose of this study was to determine the mechanism of this positive inotropic effect in ferret papillary muscles loaded with the Ca2+ indicator, aequorin. Over the range of doses from 10(-6) to 10(-3) M, flosequinan produced a 61 +/- 9% increase in peak tension that was accompanied by a corresponding increase in [Ca2+]i. This positive inotropic effect was not selectively blocked by addition to the perfusate of procaine 0.6 microM, tetrodotoxin 10(-6) M or by verapamil, 5 x 10(-8) M. In contrast, the positive inotropic effect of flosequinan, but not milrinone or hydralazine, was potentiated by prior addition of ouabain 3 nM to enhance intracellular Ca2+ via reduction of the Na+/Ca2+ exchange. Moreover, antagonists of Na+/Ca2+ exchange, including cadmium 10 microM, amiloride 600 microM and choline substitution for 1/3 Na+ in the perfusate, blocked the response to flosequinan but not hydralazine or milrinone. These results indicate that flosequinan produces a positive inotropic effect by reduction of Na+/Ca2+ exchange in mammalian myocardium. Moreover, flosequinan has the potential to interact synergistically with other positive inotropic agents such as digoxin that affect Na+/Ca2+ exchange by direct or indirect actions.

Importance of assessing changes in ventricular response to atrial fibrillation during evaluation of new heart failure therapies: experience from trials of flosequinan

This study evaluated the effects of flosequinan on ventricular rate in patients with congestive heart failure and atrial fibrillation to determine whether this agent has a facilitatory effect on atrioventricular conduction and whether such an effect may be deleterious. Flosequinan is known to have a dose-dependent positive chronotropic effect on the sinus node, but its effect on atrioventricular conduction has not been evaluated. An excessive increase in ventricular rate during the treatment of heart failure could raise a safety concern and counterbalance beneficial responses. Data were analyzed from 338 patients participating in three similarly designed placebo-controlled exercise trials with flosequinan who also underwent ambulatory electrocardiographic monitoring. The effects of two doses of flosequinan on supine, standing, ambulatory, and exercise heart rates and on exercise capacity in patients in sinus rhythm and atrial fibrillation were compared. Flosequinan increased heart rate in a dose-dependent manner, in patients both with sinus rhythm and atrial fibrillation. A 100 mg once daily dose produced significant increases, in both rhythms, ranging from 6 to 11 beats/min, in supine and standing heart rate, ambulatory heart rate, and exercise heart rate. With a dose of 75 mg twice daily, heart rates under these conditions increased by >20 beats/min in flosequinan-treated patients in atrial fibrillation, a change significantly greater than that observed with placebo or flosequinan, 100 mg once daily and also more than in patients in sinus rhythm treated with the same dose. These results indicate that flosequinan facilitates atrioventricular nodal conduction, increasing the ventricular response in atrial fibrillation, especially at higher dosages. This finding could result from a direct drug action, such as phosphodiesterese inhibition, or reflex sympathetic activation. This response is of sufficient magnitude potentially to impair left ventricular function and interfere with clinical benefit. The effect of heart-failure drugs on ventricular responses in atrial fibrillation should be examined to provide insight into potential mechanisms of both action and safety in this common patient group.

Mechanisms of the contractile effects of flosequinoxan

In guinea-pig papillary muscles the positive inotropic effect of flosequinoxan (BTS) starting at 100 mumol/l amounted to 287.6 +/- 34.2% at 300 mumol/l without any effects on time to peak tension (103.9 +/- 2%) and relaxation time (107.1 +/- 6.7% of predrug value, respectively). 10 mumol/l carbachol attenuated the positive inotropic effect of 300 mumol/l to 166.5 +/- 11.6% (n = 10). The phosphorylation state of the inhibitory subunit of troponin (TnI) and phospholamban (PLB) in [32P]-labeled guinea-pig ventricular myocytes was increased starting at 100 mumol/l amounting to 142.5 +/- 12.6% and 130.9 +/- 2.2% at 300 mumol/l, respectively (n = 5). Furthermore, BTS (300 mumol/l) decreased phosphorylase phosphatase activity by 23.1%. It is concluded that the contractile effects of BTS are accompanied by enhanced phosphorylation of regulatory proteins which could in part be due to inhibition of phosphorylase phosphatase activity.

Influence of flosequinan on autonomic tone in congestive heart failure: implications for the mechanism of the positive chronotropic effect and survival influence of long-term vasodilator administration

The vasodilator flosequinan has been shown to be effective in the management of symptoms of congestive heart failure but has been found to influence survival adversely when administered in selected doses. A moderate positive chronotropic response accompanies long-term administration of this agent, which may be associated with an activation of the neurohormonal axis that itself may contribute to the reported increase in mortality. This investigation used the technique of spectral analysis of heart rate variability to examine the autonomic response to long-term flosequinan administration in 39 patients enrolled in a double-blind placebo-controlled trial of this vasodilator to determine whether autonomic mechanisms account for the observed changes in heart rate. Although heart rate significantly increased in the flosequinan-treated patients, parasympathetic tone increased and sympathetic drive decreased compared with placebo, as reflected by high- and low-frequency heart rate variabilities, respectively. It is concluded that (1) autonomic inputs to the myocardium that would be expected to produce increases in heart rate do not result from long-term flosequinan administration; (2) accordingly, a direct positive chronotropic effect must account for the heart rate changes observed with this vasodilator; and (3) the increased mortality associated with the administration of this agent in the doses examined does not appear to result from reflex changes in autonomic tone and must result from other properties of this vasodilator.

Acute and chronic effects of flosequinan on resting and exercise haemodynamics in congestive heart failure

1 The acute and chronic (8 weeks) haemodynamic responses to oral flosequinan have been investigated in 12 male patients of mean age 58.9 years with congestive heart failure of N.Y.H.A. classes II and III. 2 Flosequinan 125 mg orally significantly reduced right atrial pressure, pulmonary artery pressure and pulmonary wedge pressure prior to and following 8 weeks chronic treatment (125 mg daily). A significant decrease in systemic pressure and an increase in heart rate were also observed with acute flosequinan prior to chronic treatment. A reduction in systemic vascular resistance and an increase in cardiac index reached significance in response to flosequinan 125 mg orally following 8 weeks of therapy. 3 In the erect position, flosequinan reduced pulmonary wedge pressure and tended to reduce systemic vascular resistance, without decreasing mean arterial pressure. 4 Following chronic treatment, there was a trend towards a reduction in pulmonary wedge pressure and an increase in cardiac index, otherwise resting and exercise haemodynamics were unchanged. 5 The response to flosequinan was similar at week 1 and after 8 weeks of treatment for all of the haemodynamic parameters. 6 Flosequinan increased bicycle exercise times and attenuated exercise-induced increases in pulmonary arterial and systemic pressures. There was a trend towards an increase in treadmill exercise time. 7 Sublingual glyceryl trinitrate (0.5 mg) and oral flosequinan (125 mg) had similar effects on right atrial pressure, pulmonary arterial and pulmonary wedge pressures at 5 min and 2 h respectively post-dosing. A small additive effect on pulmonary arterial and wedge pressures was observed.

Can further benefit be achieved by adding flosequinan to patients with congestive heart failure who remain symptomatic on diuretic, digoxin, and an angiotensin converting enzyme inhibitor? Results of the flosequinan-ACE inhibitor trial (FACET)

BACKGROUND

Angiotensin converting enzyme inhibitors, diuretics, and digoxin are each effective in treating congestive heart failure, but many patients remain symptom-limited on all three medications. This trial was designed to determine whether the addition of oral flosequinan, a new direct-acting arterial and venous vasodilator with possible dose-dependent positive inotropic effects, improves exercise tolerance and quality of life in such patients.

METHODS AND RESULTS

In a randomized, double-blind multicenter trial, 322 patients with predominantly New York Heart Association class II or III congestive heart failure and left ventricular ejection fractions of 35% or less, who were stabilized on a diuretic, angiotensin converting enzyme inhibitor, and digoxin, were treated with 100 mg flosequinan once daily, 75 mg flosequinan twice daily, or matching placebo. Efficacy was evaluated with serial measurements of treadmill exercise time, responses to the Minnesota Living With Heart Failure Questionnaire (LWHF), and clinical assessments during a baseline phase and a 16-week treatment period. After 16 weeks, 100 mg flosequinan once daily produced a significant increment in median exercise time (64 seconds at 16 weeks) compared with placebo (5 seconds), whereas the higher-dose flosequinan group did not show a statistically significant increase. Flosequinan (100 mg once daily) also improved the overall LWHF score significantly compared with placebo; both active therapies decreased the physical component, but 75 mg flosequinan twice daily was associated with a trend toward worsening of the emotional component. Most clinical assessments tended to improve on active therapy.

CONCLUSIONS

These results indicate that additional symptomatic benefit can be attained by adding flosequinan to a therapeutic regimen already including a converting enzyme inhibitor. Because in the future most patients will fall into this category, flosequinan is a potential adjunctive agent in the management of severe congestive heart failure. However, because recent evidence indicates that the flosequinan dose studied in the present trial has an adverse effect on survival, the benefit-to-risk ratio must be assessed in individual patients.