Early tolerance to hemodynamic effects of high dose transdermal nitroglycerin in responders with severe chronic heart failure

High-dose versus low-dose intravenous nitroglycerine for sympathetic crashing acute pulmonary edema: a randomised controlled trial

OBJECTIVES

Sympathetic crashing acute pulmonary edema (SCAPE) is a subset of heart failure with a dramatic presentation. The unique physiology of this condition requires a different management strategy from the conventional practice. The trial objective was to compare the efficacy of high-dose and low-dose GTN in patients with SCAPE.

METHODS

This was an open-label randomised control trial conducted in a tertiary care teaching hospital in India from 11 November 2021 to 30 November 2022. Consenting participants were randomised to high-dose GTN or conventional low-dose GTN. The primary outcome was symptom resolution at 6 hours and 12 hours. Secondary outcomes included intubation rates, admission rates, length of hospital stay, and any short-term adverse effects of GTN and major adverse cardiac events (MACE) at 30 days.

RESULTS

Fifty-four participants were included (26 high-dose GTN, 26 low-dose GTN). At 6 hours, symptom resolution was seen in 17 patients (65.4%) in the 'high-dose' group, compared with 3 (11.5%) in the 'low-dose' group (p<0.001). At 12 hours, 88.5% of patients had a clinical resolution in the 'high-dose' arm versus 19.5% in 'low-dose' arm . The low-dose group had longer median hospital stay (12 hours vs 72 hours), more frequent MACE (3.8% vs 26.9%, p=0.02) and a higher intubation rate (3.8% vs 19.2%, p=0.08). The only short-term adverse effect seen was a headache in both the groups.

CONCLUSION

In SCAPE, patients receiving high-dose GTN (>100 mcg/min) had earlier symptom resolution compared with the conventional 'low dose' GTN without any significant adverse effects.

TRIAL REGISTRATION

Clinical trial registry of India (CTRI/2021/11/037902).

Use of isosorbide dinitrate and hydralazine in African-Americans with heart failure 9 years after the African-American Heart Failure Trial

The 2013 American College of Cardiology Foundation/American Heart Association guidelines recommend combined isosorbide dinitrate (ISDN) and hydralazine to reduce mortality and morbidity for African-Americans with symptomatic heart failure (HF) and reduced ejection fraction, currently receiving optimal medical therapy (class I, level A). Nitrates can alleviate HF symptoms, but continuous use is limited by tolerance. Hydralazine may mitigate nitrate tolerance, and the ISDN-hydralazine combination in the Vasodilators in Heart Failure Trial (V-HeFT) I improved survival and exercise tolerance in men with dilated cardiomyopathy or HF with reduced ejection fraction, most notably in self-identified black participants. In the subsequent V-HeFT II, survival was greater with enalapril than with ISDN-hydralazine in the overall cohort, but mortality rate was similar in the enalapril and ISDN-hydralazine groups in the self-identified black patients. Consequently, in the African-American Heart Failure Trial (A-HeFT) in self-identified black patients with symptomatic HF, adding a fixed-dose combination ISDN-hydralazine to modern guideline-based care improved outcomes versus placebo, including all-cause mortality, and led to early trial termination. Hypertension underlies HF, especially in African-Americans; the A-HeFT and its substudies demonstrated not only improvements in echocardiographic parameters, morbidity, and mortality but also a decrease in hospitalizations, potentially affecting burgeoning HF health-care costs. Genetic characteristics may, therefore, determine response to ISDN-hydralazine, and the Genetic Risk Assessment in Heart Failure substudy demonstrated important hypothesis-generating pharmacogenetic data.

Impact of a high-dose nitrate strategy on cardiac stress in acute heart failure: a pilot study

BACKGROUND

Intravenous nitrate therapy has been shown to improve short-term outcome of acute heart failure patients treated in the intensive care unit. The potential of a noninvasive high-dose nitrate strategy in the Emergency Department and the general ward remains unknown.

METHODS

A total of 128 consecutive acute heart failure patients were either treated with standard therapy or high-dose sublingual and transdermal nitrates on top of standard of care treatment. Cardiac recovery, quantified by B-type natriuretic peptide (BNP) levels during the first 48 h, was the primary endpoint. Secondary endpoints ascertained the safety of the nitrate therapy.

RESULTS

The high nitrate group received higher doses of nitrates during the first 48 h compared to the standard therapy group [82.4 mg (46.2-120.6) vs. 20 mg (10-30) respectively, P < 0.001]. The amount of diuretics given in both groups was similar. BNP levels decreased in all patients (P < 0.0001). However, the BNP decrease was larger in the high-dose nitrate group (P < 0.0001). The larger decrease in BNP in the high-dose nitrate group was already apparent 12 h after the initiation of treatment. After 48 h BNP values decreased by an average of 29 +/- 4.9% in the high-dose nitrate strategy group compared to 15 +/- 5.4% during standard therapy. There was a strong trend towards fewer ICU admissions in the high-dose nitrate group [high-dose nitrates: 2 cases (4%) vs. standard therapy: 9 cases (13%); P = 0.06]. During the study period, no intergroup changes were observed in blood pressure, RIFLE classes of acute kidney injury or troponin T. In-hospital and 90-day outcome was similar amongst the two groups.

CONCLUSIONS

A noninvasive high-dose nitrate strategy on top of standard therapy is safe and notably accelerates cardiac recovery in patients observed on the general ward.

Safety of nitrate withdrawal in angina-free and hemodynamically stable patients with coronary artery disease

STUDY OBJECTIVES

To assess the consequences of nitrate withdrawal in angina-free and hemodynamically stable coronary patients.

DESIGN

Prospective, open, intervention study.

SETTING

Cardiology outpatient clinic of a university-affiliated municipal hospital.

PATIENTS

Angina-free patients who were hemodynamically stable for at least 3 months before study onset were enrolled. They were all regularly receiving nitrates for symptom control. Those with significant reasons to avoid stopping nitrates, such as heart failure (ejection fraction <35%) or high BP (> 160 mm Hg systolic and/or > 100 mm Hg diastolic), and noncompliant patients were excluded.

INTERVENTIONS

After providing informed consent and undergoing an exercise test (whenever possible), the participants were randomized to abruptly discontinue (study group) or continue (control group) nitrate treatment. Follow-up continued for at least 3 months after study entry.

MEASUREMENTS AND RESULTS

Eighty patients were randomized to the study group and 40 patients to the control group (mean age [+/- 1 SD], 65.5 +/- 11 years and 66.1 +/- 10.9 years, respectively; p = not significant). The first month, eight study patients (10%) had a recurrence of anginal symptoms, compared with one control subject (2.5%) [p = not significant]. All eight patients responded promptly and favorably to the resumption of nitrate administration.

CONCLUSIONS

Nitrate administration can be safely discontinued in angina-free and hemodynamically stable coronary patients who receive this medication on a regular basis. If relapse of anginal symptoms occurs, it will be within 1 month following nitrate withdrawal, and will resolve satisfactorily with reinstatement of treatment.

Potential role of type 5 phosphodiesterase inhibition in the treatment of congestive heart failure

Endothelial dysfunction is associated with impairment of aerobic capacity in patients with heart failure and may play a role in the progression of disease. Impaired endothelium-dependent vasodilation in patients with heart failure can be attributed to decreased bioavailability of nitric oxide and attenuated responses to nitric oxide in vascular smooth muscle. Impaired vasodilation in response to nitric oxide derived from vascular endothelium or organic nitrates in vascular smooth muscle may be related in part to increased degradation of the second messenger cyclic guanosine monophosphate by type 5 phosphodiesterase. Sildenafil, a specific type 5 phosphodiesterase inhibitor currently approved for the treatment of erectile dysfunction, has been shown to acutely enhance endothelium-dependent vasodilation in patients with heart failure. Further studies are warranted to characterize the safety and efficacy of type 5 phosphodiesterase inhibition in the treatment of chronic heart failure.

Effects of a nitrate-free interval on tolerance, vasoconstrictor sensitivity and vascular superoxide production

OBJECTIVES

In the present study, we tested whether a nitrate-free interval is able to prevent increases in vascular superoxide (O2*-) and the development of hypersensitivity to vasoconstrictors and whether this may result in restoration of vascular nitroglycerin (NTG) sensitivity.

BACKGROUND

Intermittent NTG-patch treatment (12 h patch on/patch-off) has been shown to increase ischemic periods in patients with stable coronary arteries, suggesting a rebound-like situation during the patch-off period. Recently, we demonstrated that long-term treatment with NTG induces tolerance, which was in part related to increases in vascular O2*- and increased vasoconstrictor sensitivity.

METHODS

New Zealand white rabbits received a continuous application of NTG patches (0.4 mg/h) or an intermittent application of NTG patches (12 h patch on, 12 h patch off) for three days. Isometric tension studies were performed with aortic rings, and vascular O2*- was estimated using lucigenin-derived chemiluminescence (5 micromol/liter). Expression of the copper/zinc (Cu/Zn) superoxide dismutase (SOD) was assessed by Western blotting, and SOD activity was measured by autooxidation of 6-hydroxydopamine.

RESULTS

Continuous treatment with NTG caused tolerance to NTG, cross-tolerance to the endothelium-dependent vasodilator acetylcholine, increased vascular O2*-, reduced Cu/Zn SOD expression and increased sensitivity to vasoconstrictors such as phenylephrine, serotonin and angiotensin II. On/off treatment with NTG improved tolerance, corrected endothelial dysfunction and decreased vascular O2*-. In addition the reduction in SOD expression was less pronounced, whereas increases in the sensitivity to vasoconstrictors such as phenylephrine and serotonin remained nearly unchanged.

CONCLUSIONS

Enhanced vasoconstrictor sensitivity may explain, at least in part, the rebound phenomena observed in patients during a 12-h NTG patch-off period.

Echo-dipyridamole stress test evaluation of isosorbide-5-mononitrate efficacy and tolerance in patients with coronary heart disease: interplay with sympathetic activity

In 22 patients with stable myocardial ischemia, we prospectively studied the short- and long-term effects of isosorbide-5-mononitrate (5-ISMN) on dipyridamole-induced myocardial ischemia, the ability of dipyridamole-stress echocardiography to evaluate nitrate tolerance, and the role of activation of the neurohumoral system in nitrate tolerance development, assessed by modifications of catecholamines plasma levels and heart rate variability. After brief treatment with 5-ISMN, dipyridamole-stress echocardiography was negative in 19 of 22 patients (p < 0.001 vs. placebo). During the sustained phase, dipyridamole-stress echocardiography was positive after both placebo and active drug (p = NS vs. placebo). Heart rate variability showed significantly higher values in power of the low frequency (LF) band and low- to high-frequency ratio (L/H), as well as significantly lower values of the power of the high-frequency (HF) band (all p < 0.001) during brief but not during sustained administration of 5-ISMN. Norepinephrine plasma levels were significantly higher (p < 0.001) during short-term 5-ISMN administration but not during the sustained phase. Our results indicate that short-term administration of 5-ISMN antagonizes dipyridamole-induced myocardial ischemia and show the loss of antiischemic efficacy in 95% of patients during sustained treatment, demonstrating that dipyridamole-stress echocardiography is a useful tool to assess the presence of nitrate tolerance. Spectral analysis of heart rate variability and norepinephrine values confirm that brief nitrate administration increases sympathetic activity, a possible crucial trigger event in the development of nitrate tolerance, whereas prolonged nitrate treatment is not associated with prolonged neurohumoral activation.

Sildenafil: a urologist's view

Erectile dysfunction (ED) is a common problem with a multifactorial aetiology. The treatment of ED has been revolutionised by the introduction of intracavernosal injections some two decades ago. However, the recent development of the orally-administered drug sildenafil (Viagra) has had a major impact on the treatment of ED. We discuss the trials with sildenafil with special reference to cardiovascular risk factors associated with ED.

Role of superoxide dismutase in in vivo and in vitro nitrate tolerance

We assessed whether pharmacological inhibition of CuZn-superoxide dismutase (SOD) mimics the molecular mechanism of either in vitro or in vivo nitrovasodilator tolerance. In endothelium-intact aortic rings from in vivo tolerant rabbits the GTN- and acetylcholine (ACh)-induced maximal relaxation was attenuated by 36 and 23%, respectively. In vitro treatment of control rings with GTN (1 h 10 microM) similarly attenuated the vasorelaxant response to GTN, but not to ACh. Formation of superoxide radicals (*O2-) in endothelium-intact rings (lucigenin-chemiluminescence) increased 2.5 fold in in vivo tolerance, but significantly decreased in in vitro tolerance. The membrane associated NADH oxidase activity was increased 2.5 fold in homogenates of in vivo tolerant aortae, but was not changed in in vitro tolerant aorta. Conversely, SOD activity and protein expression was halved in in vivo tolerance, but SOD activity was not altered by in vitro tolerance. The *O2- scavenger tiron (10 mM) effectively restored the vasorelaxant response to GTN in in vivo tolerant aortic rings, but not the reduced response to GTN in in vitro tolerant rings. Pretreatment (1 h) of vessels with diethyldithiocarbamate (DETC; 10 mM) attenuated vasorelaxant responses to GTN and ACh, increased vascular *O2- production, and inhibited SOD activity in vessel homogenates to a similar degree as observed in in vivo tolerance. DETC-treatment of in vivo-tolerant vessels induced an additional increase in *O2- production. Increased *O2- production in in vivo nitrate tolerant aorta is associated with activation of vascular NADH oxidase and inactivation of CuZnSOD. Therefore, in vivo tolerance can be mimicked by in vitro inhibition of CuZnSOD, but not by in vitro exposure to GTN, which does not affect vascular *O2- production, NADH oxidase and CuZnSOD.

Role for NADPH/NADH oxidase in the modulation of vascular tone

The endothelium modulates vascular tone by producing vasodilator and vasconstrictor substances. Of these, the best characterized and potentially most important are nitric oxide (NO.) and O2-.. These small molecules exhibit opposing effects on vascular tone and chemically react with each other in a fashion that negates their individual effects and leads to the production of potentially toxic substances, such as peroxynitrite (ONOO-). These dynamic interactions may likely have important implications, altering not only tissue perfusion but also contributing to the process of atherosclerosis. The precise O2-. source within vascular tissue remains to be determined. Recent work demonstrated that in endothelial cells as well as in vascular smooth muscle cells, a membrane-associated NAD(P)H-dependent oxidase represents the most significant O2-. source. Interestingly, this oxidase is activated upon stimulation with angiotension II, suggesting that under all conditions of an activated circulating and/or local renin-angiotensin system endothelial dysfunction secondary to increased vascular O2-. production is expected.

Double-blind, placebo-controlled study to evaluate the effect of organic nitrates in patients with chronic heart failure treated with angiotensin-converting enzyme inhibition

BACKGROUND

Organic nitrates are widely used in the treatment of chronic heart failure (CHF). No information, however, is available regarding their effect in patients already treated with ACE inhibitors.

METHODS AND RESULTS

In a randomized, double-blind, crossover design, we studied the effects of high-dose (50 to 100 mg) transdermal nitroglycerin (NTG) and placebo given daily for 12 hours in 29 patients with CHF (NYHA functional classes II to III). Exercise time (4 hours after patch application) showed a progressive improvement during NTG administration, with an increase of 38+/-35 seconds (9+/-7%) at the end of the first month (P=NS), 76+/-28 seconds (16+/-6%) at the end of the second month (P=0.01), and 117+/-34 seconds (27+/-6%) at the end of the third month (P=0.003). No significant change was seen during placebo administration (12+/-20, 5+/-26, and 19+/-28 seconds, all P=NS). Exercise time 8 hours after NTG application measured at 3 months was also significantly longer, with a difference of 87+/-28 seconds (P=0.006), but not with placebo (23+/-36 seconds, P=0.53). Assessment of quality of life and need for additional diuretics or hospitalizations for CHF failed to demonstrate a significant difference between the 2 treatment periods. In contrast, NTG decreased left ventricular end-diastolic (-2.1+/-0.1%, P<0.05) and end-systolic (-3.2+/-1.3%, P<0.05) dimensions and augmented LV fractional shortening (24.7+/-10.5%, P<0.03). The effect of placebo on these parameters was not statistically significant.

CONCLUSION

High-dose nitrate therapy significantly improves exercise tolerance and left ventricular size and systolic function in patients with chronic, mild to moderate CHF already treated with ACE inhibitors. These findings support the role of organic nitrates as an adjunctive therapy to ACE inhibitors in patients with chronic CHF.

The role of organic nitrates in the treatment of heart failure

Nitrates have been widely used in the treatment of patients with chronic congestive heart failure. Although the use of these drugs has not been approved by the Food and Drug Administration, multiple studies have shown their favorable effects. Organic nitrates have been shown to have a beneficial effect on ischemia, hemodynamic profile, magnitude of a mitral regurgitation, endothelial function, and cardiac remodeling. These drugs, when used in combination with hydralazine, have improved exercise capacity and survival. Recent studies have shown that the use of nitrates in patients already treated with standard heart failure therapy, including angiotensin converting enzyme (ACE) inhibitors, resulted in hemodynamic improvement, marked enhancement of exercise tolerance, reduction of left ventricular size, and augmentation of systolic function. These data suggest a role for organic nitrates as an adjunctive therapy to ACE inhibitors in patients with chronic heart failure and for nitrates in combination with hydralazine as an alternative treatment in patients who are intolerant to ACE inhibitors.

Long-term nitroglycerin treatment is associated with supersensitivity to vasoconstrictors in men with stable coronary artery disease: prevention by concomitant treatment with captopril

OBJECTIVES

We examined whether long-term nitroglycerin (NTG) treatment leads to an increase in sensitivity to vasoconstrictors. To assess a potential role of the renin-angiotensin system in mediating this phenomenon, we treated patients concomitantly with the angiotensin-converting enzyme (ACE) inhibitor captopril.

BACKGROUND

The anti-ischemic efficacy of organic nitrates is rapidly blunted by the development of nitrate tolerance. The underlying mechanisms are most likely multifactorial and may involve increased vasoconstrictor responsiveness.

METHODS

Forearm blood flow and vascular resistance were determined by using strain gauge plethysmography. The short-term responses to intraarterial angiotensin II (1, 3, 9 and 27 ng/min) and phenylephrine (an alpha-adrenergic agonist drug, 0.03, 0.1, 0.3 and 1 microg/min) were studied in 40 male patients with stable coronary artery disease. These patients were randomized into four groups receiving 48 h of treatment with NTG (0.5 microg/kg body weight per min) or placebo with or without the ACE inhibitor captopril (25 mg three times daily).

RESULTS

In patients treated with NTG alone, the maximal reductions in forearm blood flow in response to angiotensin II and phenylephrine were markedly greater (-64 +/- 3% and -53 +/- 4%, respectively) than those in patients receiving placebo (-41 +/- 2% and -42 +/- 2%, respectively). Captopril treatment completely prevented the NTG-induced hypersensitivity to angiotensin II and phenylephrine (-33 +/- 3% and -35 +/- 3%, respectively) but had no significant effect on blood flow responses in patients without NTG treatment (-34 +/- 2% and -37 +/- 3%, respectively).

CONCLUSIONS

We conclude that continuous administration of NTG is associated with an increased sensitivity to phenylephrine and angiotensin II that is prevented by concomitant treatment with captopril. The prevention of NTG-induced hypersensitivity to vasoconstrictors by ACE inhibition indicates an involvement of the renin-angiotensin system in mediating this phenomenon.

The physiology and pathophysiology of the nitric oxide/superoxide system

The endothelium modulates vascular tone by producing vasodilator vasoconstrictor substances. Of these, the most well characterized and potentially important are .NO and .02-. These small molecules exhibit opposing effects on vascular tone, and chemically react with each other in a fashion which negates their individual effects and leads to the production of potentially toxic substances. These dynamic interactions may likely have important implications, altering not only tissue perfusion but also contributing to the process of atherosclerosis. .NO is produced in endothelial cells by an enzyme termed nitric oxide synthase. The endothelial .NO-synthase is activated when the intracellular level of calcium is increased. This occurs in response to neurohormonal stimuli and in response to shear stress. Acetylcholine and substance P are examples of neurohumoral substances that are able to stimulate the release of nitric oxide and to assess endothelial regulation of vasomotor tone. Importantly, the vasodilator potency of nitric oxide released by the endothelium is abnormal in a variety of diseased states such as hypercholesterolemia, atherosclerosis and diabetes mellitus. This may be secondary to decreased synthesis of nitric oxide or increased degradation of nitric oxide due to superoxide anions. More recent experimental observations demonstrate increased production of superoxide in atherosclerosis, diabetes mellitus and high renin hypertension suggesting that endothelial dysfunction in these states is rather secondary to increased .NO metabolism rather than due to decreased synthesis of .NO. Superoxide rapidly reacts with nitric oxide to form the highly reactive intermediate peroxynitrite (ONOO-). Peroxynitrite can be protonated to form peroxynitrous acid which in turn can yield the hydroxyl radical (OH.). These reactive species can oxidize lipids, damage cell membranes, and oxidize thiol groups. .NO given locally, exerts potent antiatherosclerotic effects such as inhibition of platelet aggregation, inhibition of adhesion of leukocytes and the expression of leukocyte adhesion molecules. It is important to note, however, that in-vivo treatment with .NO (via organic nitrates) increases rather than decreases oxidant load within endothelial cells. It remains therefore questionable whether systemic treatment with .NO may have antiatherosclerotic properties or whether .NO may initiate or even accelerate the atherosclerotic process.

Nitrates in the treatment of congestive heart failure

Nitrates have been widely used for the treatment of patients with chronic congestive heart failure. Although the use of these drugs has not been evaluated by large-scale studies traditionally used for evaluation of new therapy, multiple studies over the years have demonstrated their favorable effects. Organic nitrates have been shown to have a beneficial effect on ischemia, hemodynamic profile, magnitude of mitral regurgitation, endothelial function, and cardiac remodeling. These drugs alone or in combination with hydralazine have improved exercise capacity, maximal oxygen consumption, cardiac function, and survival. The use of nitrates in patients with heart failure has been limited by reduced responsiveness (resistance) and early development of tolerance. Nitrate resistance is due to reduced vascular response and results in the need to use a larger dose of any nitrate preparation when used for the treatment of patients with heart failure compared to patients without heart failure. Recent information suggests that nitrate tolerance is caused by increased levels of superoxide at the vascular wall, which leads to reduced nitric oxide level and to increased sensitivity to vasoconstrictive mechanisms, such as endothelin and angiotensin II. Intermittent dosing of nitrates allowing a 12-hour nitrate-free interval is effective in preventing nitrate tolerance and is, therefore, recommended. Recent information suggests that augmentation of nitrate dose by the use of an escalating dose regimen and a concomitant use of hydralazine can prevent or overcome the effect of nitrate tolerance in patients with heart failure.

Prevention of tolerance to hemodynamic effects of nitrates with concomitant use of hydralazine in patients with chronic heart failure

OBJECTIVES

This study was designed to determine the effect of oral hydralazine on the development of nitrate tolerance in patients with chronic congestive heart failure.

BACKGROUND

Early development of nitrate tolerance with either continuous administration of intravenous or topical nitrate preparations or frequent dosing of oral nitrates leads to significant attenuation of nitrate-mediated hemodynamic and anti-ischemic effects. In recent animal experiments, prevention of nitroglycerin-induced hemodynamic tolerance with a concomitant use of hydralazine was demonstrated. This finding may have important clinical relevance.

METHODS

Twenty-eight patients with chronic heart failure due to left ventricular systolic dysfunction were randomized to receive either a continuous infusion (24 h) of nitroglycerin alone (group I, 14 patients) or concomitantly with oral hydralazine (75 mg four times a day [group II, 14 patients]). The effect of nitroglycerin in each group was evaluated by analysis of variance for repeated measures. The power of the analysis to detect a 5.4-mm Hg (20%) change in mean pulmonary artery wedge pressure was 90%.

RESULTS

Baseline hemodynamic variables as well as the initial hemodynamic response to nitroglycerin were comparable in both groups. Compared with the initial response to nitroglycerin, a significant attenuation of effect was found in group I at 24 h in mean (+/- SE) pulmonary artery pressure (27 +/- 4% vs. 10 +/- 3%, p < 0.05) and mean pulmonary artery wedge pressure (40 +/- 4% vs. 16 +/- 4%, p < 0.05). In group II, conversely, oral hydralazine prevented nitroglycerin-induced hemodynamic tolerance and resulted in a persistent effect on mean pulmonary artery and wedge pressures throughout the study period (31 +/- 3% vs. 27 +/- 4%, p = 0.13 and 37 +/- 4% vs. 34 +/- 6%, p = 0.40, respectively). In addition, the initial effect on blood pressure was attenuated at 24 h in group I (5 +/- 2% vs. 12 +/- 3%, p < 0.05) but not in group II (15 +/- 3% vs. 17 +/- 2%, p = 0.46).

CONCLUSIONS

In patients with chronic heart failure due to left ventricular systolic dysfunction, the concomitant use of oral hydralazine prevents early development of nitrate tolerance and results in a persistent nitrate-mediated hemodynamic effect on systemic and pulmonary artery and left ventricular filling pressures. These data may support the concurrent use of hydralazine in patients with heart failure treated with organic nitrates.

Prevention of nitroglycerin tolerance with diuretics

Tolerance to prolonged nitroglycerin (NTG) may be due to drug-induced intravascular expansion. To test the hypothesis that concomitant diuretics may reduce volume expansions and thus prevent NTG tolerance, we studied 23 healthy volunteers randomized to hydrochlorthiazide or placebo before and during 74-hour continuous NTG exposure. Venodilator response to NTG was tested serially with venous forearm plethysmography. In the preNTG patch phase venodilator response was similar in both the placebo and diuretic groups. Venodilator capacity was compared after "acute" (2-hour) and "chronic" (74-hour) NTG exposure with NTG patches. Attenuation to NTG was seen in the placebo group, but NTG venodilator activity was fully maintained in the diuretic group. These data suggest that diuretics may be helpful in the prevention of NTG tolerance.

Long-term vasodilator treatment with flosequinan does not lead to hemodynamic tolerance or neurohormonal activation in severe heart failure

Flosequinan is a balanced-type vasodilator with a prolonged mode of action due to an approximate 38-hour half-life of its active first metabolite, BTS 53554. As this may lead to tolerance and neurohormonal activation, the acute and long-term pharmacokinetic, hemodynamic, and neurohormonal profile of flosequinan was evaluated. On three consecutive days, 23 patients with heart failure (New York Heart Association classes II-IV), despite digitalis and diuretics, underwent invasive hemodynamic studies after receiving 100 mg oral flosequinan (day 1), placebo (day 2), and 100 mg flosequinan (day 3), followed by repeat invasive evaluation after long-term flosequinan (100 mg daily) for 17 +/- 2 weeks. On each study day, plasma flosequinan levels increased to 1.9 +/- 0.2 mg/L after 1 hour, but returned to baseline levels at 24 hours. In contrast, BTS 53554 increased progressively, reaching relatively high plateau levels (6 mg/L) during chronic therapy. First-dose flosequinan decreased the pulmonary wedge, right atrial pressure, and systemic resistance by 50, 60, and 22%, respectively, whereas the cardiac index was increased by 40%; these effects lasted for 48 hours. During long-term treatment, baseline values of the pulmonary wedge and right atrial pressure were comparable to prestudy values, whereas systemic resistance had decreased by 22%, and the cardiac index and heart rate had increased by 22 and 14%, respectively. Readministration of flosequinan did not further affect hemodynamics, apart from a moderate reduction in the pulmonary wedge and right atrial pressure. Neurohumoral activation did not occur during acute or long-term therapy. Thus, although changes in left and right heart filling pressures are attenuated during long-term treatment, flosequinan induces sustained arterial dilatation and improves cardiac pump function without activation of circulating neurohormones.

Lack of tolerance of headache and radial artery diameter during a 7 hour intravenous infusion of nitroglycerin

Nitroglycerin-(NTG)-induced headache and dilatation of the radial artery were followed in a double blind, randomized, placebo-controlled, cross-over study in 6 healthy volunteers. NTG 0.5 microgram.kg-1 x min-1 or saline were infused i.v. for 7 h, and subsequently the infusion rate was doubled for 10 min. The radial artery diameter was measured repeatedly with high frequency ultrasound and pain was scored using a 10 point verbal scale. After 5 min of NTG infusion both headache and the arterial diameter differed significantly from baseline, and no further significant change occurred. The intensity of the headache was mild to medium (median headache score 3, range 1-7). The mean dilatation of the radial artery was 36%. The dilatation in each individual, was stable over time, both during NTG and placebo, and it did not change with the double infusion rate. The headache score in each individual was more fluctuant. No tolerance either to the NTG-induced headache or arterial dilatation was observed.

Nitrate resistance and tolerance: potential limitations in the treatment of congestive heart failure

Organic nitrates are commonly used in the treatment of chronic congestive heart failure (CHF). These drugs have been shown to improve exercise capacity and reduce symptoms and in combination with hydralazine to prolong life in patients with mild-to-moderate symptoms of CHF. Recent investigations, however, have indicated that nitrate-mediated benefit to patients with CHF may be limited by resistance to their hemodynamic effects seen in many patients and by early development of tolerance. The incidence, potential mechanisms, and possible methods for prevention of nitrate resistance and tolerance in patients with chronic CHF are reviewed.

Pharmacodynamic and pharmacokinetic evaluation of a new transdermal delivery system with a time-dependent release of glyceryl trinitrate

The pharmacokinetics of glyceryl trinitrate (GTN) and its main metabolites as well as the hemodynamic effects of a new transdermal delivery system (TDS) were investigated in ten healthy male volunteers using a single blind, placebo-controlled study design with an application period of active drug of 4 successive days. The adhesive-type matrix system contains 20-mg GTN and released about 75% in a time-dependent manner. The plasma concentrations of GTN and its metabolites 1-2- and 1-3 glyceryl dinitrate reflected the time-dependent release with higher plasma concentrations during the first 12 hours than during the second 12 hours. Continuous administration of the TDS, which released 15 mg GTN/day, caused an accumulation of GTN in the plasma (about 70% greater AUC at the fourth day in comparison with the first day). The total effect per dose on the a/b-ratio of the digital pulse (height of the peak of the systolic wave divided by height of the peak of the dicrotic wave) and the reflex tachycardia were diminished by about 50% and 37%, respectively, at the fourth treatment day. The effect on systolic blood pressure measured under orthostatic conditions was blunted already 8 hours after the first application. The effect of sublingually administered GTN on digital pulse was attenuated during administration and also 1 hour after removal of the last TDS. The effect was restored 8 to 12 hours after removal of the TDS. Thus, the discontinuous release of GTN from the new system does not prevent the decline of hemodynamic efficacy during continuous therapy.

Randomized study to evaluate the relation between oral isosorbide dinitrate dosing interval and the development of early tolerance to its effect on left ventricular filling pressure in patients with chronic heart failure

BACKGROUND

Early development of nitrate tolerance has been shown in patients with chronic congestive heart failure (CHF) receiving continuous nitroglycerin therapy. The influence of dosing interval of oral isosorbide dinitrate (ISDN), the nitrate preparation most widely used for the treatment of CHF, has not been investigated.

METHODS AND RESULTS

We performed a prospective, randomized study to evaluate the effect of various regimens of oral ISDN on the development of early tolerance to its effect on left ventricular filling pressure in patients with moderate to severe CHF. Forty-four responders (20% or greater reduction in mean pulmonary artery wedge pressure lasting 1 hour or longer) were divided into four groups of 11 patients each, and randomized to receive their effective ISDN dose (40-120 mg) Q 4 hours, Q 6 hours, Q 8 hours, or t.i.d. (drug given at 0, 6, 12, and 24 hours allowing 12 hours of ISDN washout interval between the third and fourth doses). All groups demonstrated a significant and comparable reduction in LV filling pressure following administration of the first ISDN dose. Early attenuation of hemodynamic response was demonstrated with frequent dosing (Q 4 hours and Q 6 hours) ISDN. Tolerance was with a Q 8-hour regimen as demonstrated by preserved hemodynamic response to each dose. The effect of each dose, however, was short-term, with return of pulmonary artery wedge pressure to baseline level at 2 to 4 hours, resulting in an intermittent effect totaling no longer than 12 hours of the 30-hour study period. The use of a t.i.d. regimen resulted in marked attenuation of response after the third dose with complete restoration of nitrate effect following a 12-hour washout period between the third and fourth doses. ISDN plasma concentration was measured in five patients in each of the Q 4- and Q 8-hour groups. In the Q 4-hour group, plasma levels were significantly higher after administration of the last dose than after the first dose (area under the curve, 242 +/- 216 versus 123 +/- 130 ng/ml, p less than 0.05), and trough levels before administration of the second and the fifth dose (15 +/- 17 and 27 +/- 27 ng/ml, respectively) were both markedly higher than the baseline value of 2 +/- 4 ng/ml.

CONCLUSIONS

Our data demonstrate the development of tolerance and early attenuation of effect on left ventricular filling pressure with frequent oral dosing (Q 4 and Q 6 hours) with ISDN in patients with chronic CHF, which may be related to persistently elevated trough blood levels of ISDN. The development of tolerance can be reversed after a washout period of 12 hours and can be prevented with a Q 8-hour administration. These regimens, however, are limited by an inconsistent effect. Although long-term implications of these findings need further evaluation, the present study demonstrates the difficulty of maintaining a persistent ISDN-mediated reduction in left ventricular filling pressure in patients with chronic, moderate to severe CHF. These results suggest the need to use intermittent ISDN therapy allowing a daily nitrate washout interval and the rationale for combined vasodilator therapy in patients with CHF.

Nitrate tolerance in heart failure: differential venous, pulmonary and systemic arterial effects

The hemodynamic profile of tolerance to intravenous nitroglycerin was studied in 9 patients with New York Heart Association Class III to IV congestive heart failure. After rapid dosage build-up to the maximal tolerated dose (decrease in pulmonary wedge pressure to 10 mm Hg or systolic blood pressure to 90 mm Hg), nitroglycerin (525 +/- 548 micrograms/min) was administered at a constant continuous intravenous infusion for a total of 24 hours. The extent of nitrate tolerance at 24 hours was calculated as the percentage loss of the benefit achieved at time of peak effect of nitroglycerin. Tolerance had a different time course and magnitude in the venous, arterial and pulmonary circulations. At 24 hours, right atrial pressure and pulmonary vascular resistance returned to control values in most patients, while 40 to 50% of the effect on systemic vascular resistance, cardiac index and pulmonary wedge pressure was maintained. These findings emphasize the importance of precise definitions in studies relating to nitrate tolerance.

Duration and reproducibility of initial hemodynamic effects of flosequinan in patients with congestive heart failure

The duration and reproducibility of hemodynamic effects of flosequian, a direct-acting, balanced-type vasodilator, were studied in 19 heart failure patients (NYHA class 3.0 +/- 0.7) receiving 100 mg orally (day 1), placebo (day 2), and again 100 mg (day 3). Flosequinan immediately reduced systemic and pulmonary resistance (23% and 35%, respectively, at 60-90 minutes postdrug) and decreased pulmonary wedge, right atrial, mean pulmonary artery, and mean arterial pressure by 38%, 50%, 25%, and 7%, respectively. Concomitantly, cardiac output, and stroke volume and work increased by 26%, 20%, and 22%, respectively. Most hemodynamic effects persisted for 48 hours. In contrast, changes in pulmonary wedge and arterial pressures, stroke volume, and stroke work only lasted for 2-12 hours. Maximum absolute changes on day 3 were generally comparable with first-dose effects with, again, long-lasting effects on systemic resistance and cardiac output. However, changes in pulmonary artery, wedge, and resistance were significantly shorter than after first dose administration. These data indicate sustained and reproducible arterial dilating effects of flosequinan, but less pronounced and shorter lasting pulmonary arterial and venodilator properties.

Nitrates: why and how should they be used today? Current status of the clinical usefulness of nitroglycerin, isosorbide dinitrate and isosorbide-5-mononitrate

Nitrates are highly effective both in terminating acute attacks of angina pectoris and in the prophylaxis of symptomatic and asymptomatic myocardial ischemia. Preload reduction by venodilatation is the prevailing mechanism of nitrates in patients with chronic stable angina and is the unique feature distinguishing them from beta and calcium-channel blockers. Nitrates dilate coronary arteries not only in pre- and poststenotic vessels, but also in eccentric lesions. In patients with endothelial dysfunction, nitrates seem to be the physiological substitute for endothelium-derived relaxing factor. During the past decade, however, there has been substantial evidence of a clinically relevant loss of the anti-ischemic effects ("nitrate tolerance"). Many studies with oral dosing of isosorbide dinitrate or isosorbide-5-mononitrate at least three times daily have proven nitrate tolerance in patients with coronary artery disease and/or congestive heart failure. Complete loss of anti-ischemic effects after repetitive, continuous patch attachments has also been found. As we first showed in 1983, intermittent therapy with once-daily ingestion of high-dose sustained-release isosorbide dinitrate was successful in preventing the development of tolerance. Similarly, tolerance to isosorbide-5-mononitrate also does not develop when it is ingested once daily. It is now generally accepted that a daily low-nitrate interval is required to prevent tolerance development. Although the minimal patch-free interval required to prevent tolerance needs further investigation, a 12-h patch-free interval should prevent tolerance in most patients. The prolonged duration of action of once-daily high-dosage administration of sustained-release formulations, the improved patient compliance with a single daily administration, and the increased likelihood of maximal anti-ischemic effects are important reasons for recommending high single daily doses of isosorbide dinitrate or isosorbide-5-mononitrate.