New perspectives on therapeutic application of nitrates as vasodilator agents for severe chronic heart failure

Development of tolerance to nitrate therapy in chronic congestive heart failure

In several studies the nitrate effects on central hemodynamics during less than 24 hours have been evaluated in heart failure. Higher doses than in angina have been used. A pronounced response is seen acutely. An attenuation has been reported after 12-24 hours. A relation to continuous (intravenous, transdermal) administration of nitroglycerin has been proposed, but it is not clear. During chronic treatment with ISDN a tolerance is not obvious within 12 weeks. The heart failure patient has a different neurohumoral situation compared to angina patients. This could be one reason for differences in tolerance development during nitrate therapy.

Influence of hemodynamic changes on neuroendocrine response in acute heart failure

We studied 15 patients with acute deterioration of chronic left ventricular heart failure. We compared the influence of reduction of ventricular filling pressures with glyceryl trinitrate versus reduction of ventricular filling pressures with diuretics on plasma concentration of epinephrine, norepinephrine, aldosterone and renin activity. Reduction of ventricular filling pressures with glyceryl trinitrate had no influence on plasma concentrations of epinephrine, norepinephrine, aldosterone and renin activity. After reduction of ventricular filling pressures with diuretics plasma concentrations of epinephrine, norepinephrine and aldosterone decreased, while plasma renin activity did not change. We conclude that there is a difference in the influence of reduction of ventricular filling pressures with glyceryl trinitrate versus reduction of ventricular filling pressures with diuretics, on neuroendocrine response in patients with acute deterioration of left ventricular heart failure. Thus some of the neuroendocrine effects of glyceryl trinitrate are likely to be different from those of diuretics, though that they both produce a reduction in left ventricular filling pressure.

Investigation of a possible pharmacokinetic interaction between ibopamine and isosorbide-5-mononitrate

The possibility of a pharmacokinetic interaction between isosorbide-5-mononitrate (5-ISMN) and epinine, the active metabolite of ibopamine, has been investigated in 8 healthy male subjects given single doses of 200 mg ibopamine and 20 mg 5-ISMN, separately and together. The plasma 5-ISMN concentration-time profile was the same whether 5-ISMN was administered concomitantly with ibopamine or alone [AUC(o-t): 2.24 micrograms.ml-1.h after 5-ISMN alone, 2.16 micrograms.ml-1.h after 5-ISMN+ibopamine]. The plasma concentrations of total and free epinine and the urinary recovery of total epinine, homovanillic acid and dihydroxyphenylacetic acid, too, were not different when ibopamine was administered alone or concomitantly with 5-ISMN. The intake of ibopamine did not change the blood pressure and heart rate. The decrease in diastolic blood pressure induced by 5-ISMN was not influenced by concomitant intake of ibopamine. The observations suggest that in healthy volunteers there is no pharmacokinetic interaction between 5-ISMN and ibopamine.

Cardiovascular profile of 5 novel nitrate-esters: a comparative study with nitroglycerin in pigs with and without left ventricular dysfunction

1. Four cumulative 10 min intravenous infusions of 0.05, 0.2, 0.5 and 2.0 mg min-1 were used to compare the cardiovascular profile of 5 novel nitrate-esters dissolved in Intralipid 10% to that of nitroglycerin (GTN) in conscious pigs. 2. Infusion of Intralipid 10% alone had no effect on any of the systemic haemodynamic parameters. GTN infusions decreased mean arterial blood pressure dose-dependently from 94 +/- 2 mmHg to 79 +/- 3 mmHg (P less than 0.05) and raised cardiac output from 2.74 +/- 0.09 l min-1 to 3.40 +/- 0.18 l min-1 (P less than 0.05) due to an increase in heart rate (by up to 43 +/- 3%), as stroke volume decreased slightly. Systemic vascular resistance decreased (by 32 +/- 3%) and left ventricular end-diastolic pressure fell from 5.2 +/- 0.4 mmHg to 2.2 +/- 0.5 mmHg (both P less than 0.05). 3. The novel compounds CEDO 8811, CEDO 8834 and CEDO 8901 increased cardiac output only at the highest dose (7%, 8% and 9%, respectively). There was no change in mean arterial blood pressure as the increase in cardiac output was counterbalanced by arterial vasodilatation. All three compounds reduced left ventricular end-diastolic pressure slightly. 4. CEDO 8816 was a more potent arterial and venodilator than the aforementioned CEDO compounds, as the decreases in systemic vascular resistance and left ventricular end-diastolic pressure were already significant at lower doses. The fall in stroke volume was fully compensated by the increase in heart rate and as a result cardiac output increased by 11 +/- 3% (P less than 0.05) at the highest dose. 5. CEDO 8956 was the most potent vasodilator of the novel compounds and exhibited a cardiovascular profile similar to that of GTN. Left ventricular end-diastolic pressure decreased significantly during infusion of 0.2mgmin-'. Mean arterial blood pressure decreased by 11 +/- 2% (P < 0.05) in spite of an increase in cardiac output by up to 20 +/- 2% (P < 0.05), due to a decrease (by 27 +/- 1%, P <0.05) in systemic vascular resistance. The increases in heart rate (20 +/- 5%, P < 0.05) and LVdP/dtmax (38 +/- 4%, P < 0.05) were, however, considerably less after CEDO 8956 than after GTN. 6. The potential of CEDO 8956 in the treatment of chronic left ventricular dysfunction was evaluated during administration to conscious pigs (21-23 kg), in which the left circumflex coronary artery was ligated 4 weeks earlier. In these animals, baseline values for cardiac output and LVdP/dtx were lower and those of systemic vascular resistance and left ventricular end-diastolic pressure were higher than in the first group of experiments. 7. Both GTN and CEDO 8956 in doses of 0.05 to 2.0 mg inm increased cardiac output dosedependently (by up to 34% and 19%, respectively). The decrease in systemic vascular resistance was larger with GTN (35%) than with CEDO 8956 (17%), which resulted in a 13% decrease in mean arterial pressure during infusion of GTN, whereas there was no change in mean arterial pressure during infusion of CEDO 8956. Both compounds increased LVdP/dt,,,,X (by 48% and 30%, respectively) and lowered left ventricular end-diastolic pressure to normal levels. 8. At a dose of 1.0Omg min- 1, both GTN and CEDO 8956 increased left ventricular blood flow parallel to the increase in myocardial oxygen demand. At this dose, GTN also caused vasodilatation in the vascular beds of the brain, kidneys and adrenals. With CEDO 8956 no significant changes were achieved. 9. We conclude that the cardiovascular profile of CEDO 8956 in both normal animals and in animals with chronic left ventricular dysfunction warrants further study on its usefulness in the treatment of a number of cardiovascular disorders.

Effect of isosorbide dinitrate on cardiac output in severe cardiac failure: relation to initial hemodynamics, ventricular volume, and the preload reserve mechanism

Isosorbide dinitrate (ISDN) improves the clinical and hemodynamic state of patients with heart failure, but may cause dizziness and syncope. To characterize patients in whom cardiac output falls with high-dose nitrate therapy and to examine further the pathophysiology of the fall in cardiac output in these patients, we studies the effect of sublingual ISDN on forward cardiac output in 14 patients with severe cardiac failure (New York Heart Association grades 3-4). We examined systolic and diastolic left ventricular (LV) function from pressure and volume analyses of LV function. After administration of 15 mg ISDN, cardiac output was either unaltered or increased in 7 patients (Group 1) (11 +/- 12%, mean +/- SD), and decreased in 7 (Group 2) (-13 +/- 10%) (Group 1 vs. 2, p less than 0.002). Initial systemic arterial pressure, LV ejection fraction, wedge and LV transmural filling pressures were similar in both groups, but Group 2 patients had a lower systemic vascular resistance (p = 0.07) and tended to have a larger initial LV end-diastolic volume and increased end-diastolic compliance; following ISDN the decrease in LV filling pressure and end-diastolic volume was larger and the product of the changes greater (p less than 0.02). Thus ISDN decreases filling pressure and improves forward cardiac output in some patients with congestive heart failure, but large doses may decrease cardiac output in a subset of patients who have a lower systemic vascular resistance and a larger more compliant ventricle, maintaining forward blood flow predominantly by a preload reserve mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

Current management of hypertensive emergencies

A number of potent and rapidly acting pharmacological agents are available to achieve safe, rapid, and controlled blood pressure reduction in most hypertensive crises. While sodium nitroprusside remains the drug of choice in many hypertensive emergencies, several newer agents are now available that may prove to be acceptable alternatives in the management of certain cases. Glyceryl trinitrate (nitroglycerin) and labetalol may be advantageous in patients with significant coronary artery disease. When adequate facilities to monitor continuous infusion of sodium nitroprusside are not immediately available, the intermittent minibolus administration of diazoxide or labetalol or the use of sublingual or oral nifedipine prove useful. A thorough knowledge of the pharmacological properties and proper indications of the currently used agents is essential for optimum management of the critically ill hypertensive patient.

Use of nitrates in acute and chronic congestive heart failure

The literature available on the use of nitrates (glyceryl trinitrate, isosorbide dinitrate and isosorbide 5-mononitrate) as various formulations (oral, buccal, sublingual, transdermal and intravenous) in the treatment of acute and chronic congestive heart failure is reviewed. There are adequate data on the acute haemodynamic effects of these preparations, but little information is available on the long term use of nitrates in chronic congestive heart failure. The exception is isosorbide dinitrate, which, in combination with hydralazine, has been shown to reduce mortality.

The role of vasodilator therapy in the treatment of severe chronic heart failure

The rationale for the use of vasodilating agents in the treatment of congestive heart failure is to reverse the systemic vasoconstriction that characterises patients with this disorder, and which may further limit cardiac performance. Nitrates were the first vasodilators used, followed by arterial vasodilators (hydralazine, minoxidil), alpha-adrenergic blockers (prazosin, trimazosin) and, more recently, calcium antagonists, ACE inhibitors, beta-agonists and phosphodiesterase inhibitors. The choice of vasodilator should be based on consideration of overall benefit-risk profiles. Consideration of pharmacological action together with classification of patients into haemodynamic subsets has been used as a basis from which to initiate vasodilator therapy. However, such a classification may not lead to a logical choice of drug and there is no evidence to suggest that patients so selected do better when given long term treatment with peripherally specific drugs than with agents that are not tailored to pretreatment haemodynamic variables. Moreover, changes in central haemodynamics after administration of specific vasodilator drugs may differ from those expected on the basis of their presumed actions on the peripheral vasculature. Dosage requirements are difficult to predict with many vasodilator drugs. Traditionally, such requirements have been established by titrating vasodilating drugs to achieve an arbitrarily defined haemodynamic response. However, there is little correlation between haemodynamic end-points and clinical efficacy in patients with heart failure, and short and long term haemodynamic responses to vasodilator drugs are not necessarily related. Drug-specific haemodynamic and clinical tolerance occurs during the course of treatment with all vasodilator drugs; the extent and frequency with which it develops differs between agents. Tolerance is thought to arise from a reduction in drug receptor affinity and/or density or activation of counter-regulatory forces (mainly neurohormonal) that limit the magnitude of vasodilatation that can be achieved. Development of tolerance to a single agent does not usually preclude efficacy of other agents. ACE inhibitors have been associated with a relatively low incidence of tolerance. This may relate to their natriuretic effect and ability to decrease the degree of neurohormonal activation, actions not shared by other vasodilators. Tolerance is the principal reason for failure of prazosin and nitrates as therapeutic agents in severe chronic heart failure.(ABSTRACT TRUNCATED AT 400 WORDS)

Pharmacology of nitroglycerin and long-acting nitrates

Organic nitrates are available in a remarkably diverse variety of formulations, including sublingual, buccal and oral tablets, capsules, topical creams, ointments, patches, tapes, inhalable sprays and intravenous solutions. Although not all of these formulations are available in the United States, the array of drugs and dosages approved for use is extensive. It is only by weighing the pharmacologic properties of these agents against the patient's clinical status and needs that a concise and appropriate treatment regimen may be derived. Numerous recent studies have confirmed the protracted efficacy of the organic nitrates in the treatment of patients with angina pectoris and congestive heart failure (CHF) as evidenced by improvements in cardiac hemodynamics and desired clinical parameters. It is appropriate that the patient's dosage of nitrates be administered with a formulation most likely to be both clinically effective and well tolerated. The use of nitroglycerin and isosorbide dinitrate in the acute and chronic treatment of CHF will be discussed in the context of their unique pharmacologic and pharmacokinetic properties. A rationale for the most efficacious use of these agents will be presented. Tolerance phenomena and adverse effects (i.e., headache) will also be discussed from the perspective of their significance in chronic nitrate therapy.

Mechanisms of nitrate action in patients with severe left ventricular failure: conceptual problems with the theory of venosequestration

Nitroglycerin and other organic nitrates exert a number of favorable effects on the circulation of patients with severe congestive heart failure, and these effects mediate the short- and long-term hemodynamic and clinical improvement that follows treatment with these drugs. Although these agents are potent dilators of systemic venous capacitance vessels, present evidence indicates that they do not exert their beneficial hemodynamic and clinical effects by decreasing venous return to the heart. Rather, their ability to dilate pulmonary and systemic resistance vessels offsets any decrease in cardiac output that might be expected to occur from a decrease in venous return. Of equal importance, the increase in output of the left side of the heart that results from drug-induced pulmonary and systemic vasodilation prevents any decrease in venous return to the right side of the heart that might be expected to accompany an increase in systemic venous capacitance. The net effect of these two interacting forces is not only to keep cardiac output and venous return constant but also to translocate blood volume from the pulmonary circulation and left ventricle to the systemic vessels. In addition, nitrates also relieve subendocardial ischemia and favorably alter pressure-volume relationships in the left ventricle. These observations support the conclusion that the complex cardiovascular responses to organic nitrates in patients with congestive heart failure cannot be adequately summarized by the single concept of preload reduction.

Comparative effects of captopril and isosorbide dinitrate on pulmonary arteriolar resistance and right ventricular function in patients with severe left ventricular failure: results of a randomized crossover study

We compared the short-term hemodynamic effects of isosorbide dinitrate (40 mg orally) and captopril (25 mg orally) in 18 patients with severe chronic heart failure in a randomized, crossover study conducted on consecutive days. Captopril and isosorbide dinitrate produced similar decreases in systemic vascular resistance, but whereas nitrate therapy decreased pulmonary arteriolar resistance significantly, captopril did not; the difference between the two drugs was highly significant (-25% vs -5%, p less than 0.001). Left ventricular filling pressures declined similarly with both captopril (-10.5 mm Hg) and with isosorbide dinitrate (-9.3 mm Hg), but because pulmonary arteriolar resistance fell significantly with nitrate therapy, mean right atrial pressure decreased more with isosorbide dinitrate than with captopril (-5.4 vs -2.8 mm Hg, respectively; p less than 0.001). Although systemic resistance declined similarly with both drugs, cardiac index increased more with nitrate therapy than during converting-enzyme inhibition (+0.47 vs +0.23 L/min/m2) (p less than 0.01), and therefore mean arterial pressure fell less with isosorbide dinitrate than with captopril (-10.5 mm Hg vs -16.7 mm Hg); p less than 0.05); two patients developed symptomatic hypotension with captopril, whereas none did so with the nitrate. The difference in the effects of the two drugs on cardiac index was not due to differences in their effects on heart rate, since heart rate fell similarly with both drugs, and thus both drugs produced similar increases in stroke volume index. These data indicate that, in patients with severe chronic heart failure, nitrates exert favorable dilating effects on the pulmonary circulation not shared by captopril.(ABSTRACT TRUNCATED AT 250 WORDS)

Conceptual dilemmas in the classification of vasodilator drugs for severe chronic heart failure. Advocacy of a pragmatic approach to the selection of a therapeutic agent

Two distinct systems of classifying vasodilator drugs have been developed over the past decade in an attempt to guide the choice of a therapeutic agent for the patient with severe heart failure, but the merits and utility of these systems have not been critically evaluated. Vasodilator drugs may be categorized according to their peripheral site of action: an agent may exert its effects preferentially on systemic arteries, systemic veins, or on both circulations. However, changes in the peripheral circulation cannot be directly translated into an improvement in central hemodynamic variables; furthermore, immediate hemodynamic responses may not be predictive of long-term clinical efficacy. Hence, there is no evidence that characterization of patients into hemodynamic subsets determined by the findings of right heart catheterization improves the clinical outcome of vasodilator therapy in chronic heart failure. An alternative classification system groups vasodilator drugs according to their mechanism of action: an agent may possess direct vasodilating effects or may exert its actions via selective neurohumoral inhibition. However, attempts to identify patients who might be most responsive to neurohumoral antagonism by measuring plasma renin activity or circulating levels of catecholamines before treatment have not been successful in predicting the clinical responses to therapy. Because neither system of drug classification provides the clinician with useful therapeutic guidelines, patients with severe heart failure appear to be best managed using a pragmatic approach in which specific drugs that produce predictable therapeutic benefits with a low frequency of side effects are utilized preferentially. Among presently available vasodilator agents, only captopril and oral isosorbide dinitrate have been shown to produce consistent hemodynamic and clinical improvement with an acceptable degree of adverse reactions.

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.