The daylong pattern of the antianginal effect of long-term three times daily administered isosorbide dinitrate

2018 Guidelines of the Taiwan Society of Cardiology, Taiwan Society of Emergency Medicine and Taiwan Society of Cardiovascular Interventions for the management of non ST-segment elevation acute coronary syndrome

In Taiwan, the incidence of non-ST segment elevation acute coronary syndrome (NSTE-ACS) continues to increase in recent years. The purpose of this guideline is to help health care professionals in Taiwan to use adequate tests and treatments for management of NSTE-ACS. For rapid diagnosis, in addition to history and physical examination, 0/3 h rapid diagnosis protocol with high sensitivity cardiac troponin assay is recommended in this guideline. Dual antiplatelet and anticoagulation therapies are important parts in the initial treatment. Risk stratification should be performed to identify high risk patients for early coronary angiography. Through evaluation of the coronary anatomy and other clinical factors, the decision for coronary revascularization, either by percutaneous coronary intervention or coronary artery bypass grafting, should be decided by the heart team. The duration of dual antiplatelet therapy should be given for at least 12 months after discharge. Other secondary preventive medications are also recommended for long term use.

The risk of cardiovascular side effects with anti-anginal drugs

INTRODUCTION

Angina pectoris is a common presenting symptom of underlying coronary artery disease or reduced coronary flow reserve. Patients with angina have impaired quality of life; and need to be treated optimally with antianginal drugs to control symptoms and improve exercise performance. A wide range of antianginal medications are approved for the treatment of angina, and often more than one class of antianginal drugs are used to adequately control the symptoms. This expert opinion highlights the likely cardiac adverse effects of available antianginal drugs, and how to minimize these in individual patients and especially during combination treatment. Areas covered: All approved antianginal drugs, including the older and newly approved medications with different mechanism of action to the older drugs as well as some of the unapproved herbal medications. The safety profiles and potential cardiac side effects of these medications when used as monotherapy or as combination therapy are discussed and highlighted. Expert opinion: Because of the different cardiac safety profiles and possible side effects, we recommend selection of initial drug or adjustment of therapy based on the resting heart rate; blood pressure, hemodynamic status; and resting left ventricular function, concomitant medications and any associated comorbidities.

Vasodilator Therapy: Nitrates and Nicorandil

Nitrates have been used to treat symptoms of chronic stable angina for over 135 years. These drugs are known to activate nitric oxide (NO)-cyclic guanosine-3',-5'-monophasphate (cGMP) signaling pathways underlying vascular smooth muscle cell relaxation, albeit many questions relating to how nitrates work at the cellular level remain unanswered. Physiologically, the anti-angina effects of nitrates are mostly due to peripheral venous dilatation leading to reduction in preload and therefore left ventricular wall stress, and, to a lesser extent, epicardial coronary artery dilatation and lowering of systemic blood pressure. By counteracting ischemic mechanisms, short-acting nitrates offer rapid relief following an angina attack. Long-acting nitrates, used commonly for angina prophylaxis are recommended second-line, after beta-blockers and calcium channel antagonists. Nicorandil is a balanced vasodilator that acts as both NO donor and arterial K(+) ATP channel opener. Nicorandil might also exhibit cardioprotective properties via mitochondrial ischemic preconditioning. While nitrates and nicorandil are effective pharmacological agents for prevention of angina symptoms, when prescribing these drugs it is important to consider that unwanted and poorly tolerated hemodynamic side-effects such as headache and orthostatic hypotension can often occur owing to systemic vasodilatation. It is also necessary to ensure that a dosing regime is followed that avoids nitrate tolerance, which not only results in loss of drug efficacy, but might also cause endothelial dysfunction and increase long-term cardiovascular risk. Here we provide an update on the pharmacological management of chronic stable angina using nitrates and nicorandil.

Challenges with nitrate therapy and nitrate tolerance: prevalence, prevention, and clinical relevance

Nitrate therapy has been an effective treatment for ischemic heart disease for over 100 years. The anti-ischemic and exercise-promoting benefits of sublingually administered nitrates are well established. Nitroglycerin is indicated for the relief of an established attack of angina and for prophylactic use, but its effects are short lived. In an effort to increase the duration of beneficial effects, long-acting orally administered and topical applications of nitrates have been developed; however, following their continued or frequent daily use, patients soon develop tolerance to these long-acting nitrate preparations. Once tolerance develops, patients begin losing the protective effects of the long-acting nitrate therapy. By providing a nitrate-free interval, or declining nitrate levels at night, one can overcome or reduce the development of tolerance, but cannot provide 24-h anti-anginal and anti-ischemic protection. In addition, patients may be vulnerable to occurrence of rebound angina and myocardial ischemia during periods of absent nitrate levels at night and early hours of the morning, and worsening of exercise capacity prior to the morning dose of the medication. This has been a concern with nitroglycerin patches but not with oral formulations of isosorbide-5 mononitrates, and has not been adequately studied with isosorbide dinitrate. This paper describes problems associated with nitrate tolerance, reviews mechanisms by which nitrate tolerance and loss of efficacy develop, and presents strategies to avoid nitrate tolerance and maintain efficacy when using long-acting nitrate formulations.

Side effects of using nitrates to treat angina

Nitrates are very effective antianginal and anti-ischaemic agents. Provision of a long nitrate-free interval or low plasma nitrate levels prior to the morning dose prevents the loss of clinical efficacy by preventing the development of tolerance. However, side effects during nitrate therapy are common. Headache is the most common side effect of nitrates; often dose-related and reported by up to 82% of patients in placebo-controlled trials. Nearly 10% of patients are unable to tolerate nitrates due to disabling headaches or dizziness. In others, headaches are mild-to-moderate in severity and either resolve or diminish in intensity with continued nitrate therapy. Nitrate-induced hypotension is common, but often asymptomatic. In rare instances, nitrate-induced hypotension is severe and accompanied by marked slowing of the heart rate and syncope. Use of nitrates in patients who experience syncope after administration of nitrates is contraindicated. Nitrates rarely cause coronary steal and myocardial ischaemia. Nitrate rebound may occur and patients may experience nocturnal anginal episodes during intermittent therapy with nitroglycerin patches. Administration of nitrates is contraindicated with concomitant use of phosphodiesterase-5 inhibitors used for the treatment of erectile dysfunction, as combination therapy may lead to profound hypotension and even death. There are disturbing observational reports in the literature that continuous, prolonged use of nitrates may lead to increased mortality and recurrent myocardial infarctions. Large, randomised, placebo-controlled studies are needed to confirm or refute these reports; until then, the use of nitrates to treat angina is here to stay.

Treatment of Perioperative Myocardial Ischemia

Prevention and treatment of myocardial ischemia re mains a central focus of perioperative care. Myocardial ischemia is best understood in terms of myocardial oxygen supply and demand ratios. Conventional ther apy includes nitrates, β-blockers, and calcium channel blockers. In all 3 drug classes, ischemia is reduced by either improving supply, decreasing demand, or both. More recent investigation evaluates these medications either as prophylactic therapy or as a component of long-term risk reduction for cardiac morbid events. Newer therapies, including anticoagulation, pain ther apy, normothermia, central neuroaxial techniques, and other therapies, are reviewed.

Smooth muscle cell expression of type I cyclic GMP-dependent protein kinase is suppressed by continuous exposure to nitrovasodilators, theophylline, cyclic GMP, and cyclic AMP

A key component of the nitric oxide-cyclic guanosine monophosphate (cGMP) pathway in smooth muscle cells (SMC) is the type I GMP-dependent protein kinase (PK-G I). Activation of PK-G I mediates the reduction of cytoplasmic calcium concentrations and vasorelaxation. In this manuscript, we demonstrate that continuous exposure of SMC in culture to the nitrovasodilators S-nitroso-N-acetylpenicillamine (SNAP) or sodium nitroprusside (SNP) results in approximately 75% suppression of PK-G I mRNA by 48 h. PK-G I mRNA and protein were also suppressed by continuous exposure to cGMP analogues 8-bromo- and 8-(4-chlorophenylthio) guanosine-3,5-monophosphate or the cAMP analogue dibutyryl cAMP. These results suggest that activation of one or both of the cyclic nucleotide-dependent protein kinases mediates PK-G I mRNA suppression. Using isoform-specific cDNA probes, only the PK-G I alpha was detected in SMC, either at baseline or after suppression, while PK-G I beta was not detected, indicating that isoform switch was not contributing to the gene regulation. Using the transcription inhibitor actinomycin D, the PK-G I mRNA half-life in bovine SMC was observed to be 5 h. The half-life was not affected by the addition of SNAP to actinomycin D, indicating no effect on PK-G I mRNA stability. Nuclear runoff studies indicated a suppression of PK-G I gene transcription by SNAP. PK-G I suppression was also observed in vivo in rats given isosorbide dinitrate in the drinking water, with a dose-dependent suppression of PK-G I protein in the aorta. PK-G I antigen in whole rat lung extract was also suppressed by administration of isosorbide or theophylline in the drinking water. These data may contribute to our understanding of nitrovasodilator resistance, a phenomenon resulting from continuous exposure to nitroglycerin or other nitrovasodilators.

Nitrate tolerance, rebound, and their clinical relevance in stable angina pectoris, unstable angina, and heart failure

Vascular tolerance develops rapidly in isolated vascular strips exposed to millimolar concentrations of nitroglycerin. Several mechanisms, including depletion of sulfhydryl groups, reduced biotransformation of nitrates to NO or nitrosothiols, oxygen free radical injury, and downregulation of a membrane-bound enzyme or a nitrate receptor, have been proposed, but the exact mechanism responsible for in-vitro tolerance remains unknown. In-vivo tolerance of the beneficial effects of nitrates on hemodynamics, myocardial ischemia, and exercise performance develops rapidly. It has been suggested, but remains to be proven, that development of venous tolerance and not arterial tolerance is responsible for the attenuation of nitrate effects during long-term nitrate therapy. Several mechanisms, including neurohormonal activation, depletion of sulfhdryl groups, and the shift of fluid from the extravascular to intravascular compartment have been implicated. However, the use of agents to counteract these mechanisms (ACE inhibitors, sulfhydryl donors, diuretics) has produced conflicting results. Thus, at present the mechanism responsible for in vivo tolerance to nitrates remains unknown. Both in vitro and in vivo vascular tolerance to nitrates can be prevented or minimized by providing nitrate-free or low-nitrate intervals. However, during nitrate-free periods, rebound phenomena (rest angina in patients with ischemic heart disease or a deterioration in exercise performance prior to the renewal of the morning dose in patients with stable angina) remain a clinical concern. When treating patients with stable angina pectoris, it must be recognized that none of the nitrate preparations or formulations can provide round-the-clock antianginal or antiischemic prophylaxis. In these patients, beneficial antianginal and antiischemic effects of nitrates for 10-14 hours during the daytime can be maintained by using formulations and dosing regimens that avoid or minimize the development of tolerance (standard formulation of isosorbide-5-mononitrate, 20 mg in the morning and 7 hours later; slow-release formulation of isosorbide-5-mononitrate, 120-240 mg once a day; or nitroglycerin patch delivering 0.6 nitroglycerin per hour for 10-12 hours each day). Only the patch on and off treatment is associated with nitrate rebound. Although intermittent nitrate therapy is not associated with the development of tolerance, this strategy cannot be recommended for treating unstable angina because rebound angina during nitrate-free periods complicates clinical decision making. In the acute phase of unstable angina, continuous treatment with intravenous nitroglycerin is recommended because it permits rapid up- or down-titration. Tolerance towards antianginal and antiischemic effects does develop in a substantial number of patients with 24 hours, but this can be overridden by dose escalation and restoration of the therapeutic effectiveness of nitroglycerin. Tolerance towards the beneficial effects of nitrates on hemodynamics and on exercise performance also develops rapidly during continuous or long-term nitrate therapy, and for these reasons nitrates are not used as first-line therapy to treat chronic heart failure. In combination with hydralazine, high-dose isosorbide dinitrate (30-40 mg four times a day) improves survival, but this combination therapy is inferior to ACE inhibitors.

Organic nitrates: new formulations and their clinical advantages

The organic nitrates have been used for more than a century in the management of patients with myocardial ischemia. The most commonly used agents at this time include nitroglycerin, isosorbide dinitrate, and isosorbide-5-mononitrate. These agents all exert their therapeutic effects through biodegradation to nitric oxide, which stimulates guanylate cyclase in vascular smooth muscle cells with the production of cyclic guanosine monophosphate. The latter induces vasodilation by reducing the availability of ionized calcium to the contractile proteins. Tolerance to the organic nitrates occurs when the agents are administered in an attempt to provide therapeutic effects throughout 24 hours each day. There are probably several mechanisms responsible for nitrate tolerance, but there is no evidence at this time that concurrent medications will modify the development of tolerance. The only available method at this time is to give these agents intermittently to provide a period of washout. In so doing, it is possible to provide therapeutic nitrate effects for approximately 12 hours throughout each 24-hour period.

Anti-ischemic effects of first and second dose of 20 mg isosorbide dinitrate administered 5 hours apart: attenuation of effects despite rising plasma concentration

Based on evidence that there may be early tolerance development even within the first daily cycle of treatment, this study was undertaken to evaluate the duration and extent of the antiischemic effects of two 20 mg doses of isosorbide dinitrate as used in a well-established regimen documented to maintain effectiveness during long-term treatment. Ischemia parameters were analyzed at 2 and 4 1/2 hours after the first dose as well as at 2 and 7 hours after the second dose given 5 hours later. The studies were performed in 10 male patients with documented coronary artery disease using bicycle ergometry and a double-blind, randomized, placebo-controlled, crossover protocol. ST-segment depression was reduced by 59% (p < 0.0005) at 2 hours and by 42% (p < 0.01) at 4 1/2 hours after the first tablet and by 38% (p < 0.005) at 2 hours and by 15% (p < 0.05) at 7 hours after the second tablet. Increments in ischemia-free workload capacity amounted to 112% (p < 0.005) and to 41% (p < 0.05) after the first tablet and 68% (p < 0.05) and 38% (p < 0.05) at 2 and 7 hours after the second tablet. At 2 and 4 1/2 hours after the first tablet, plasma concentrations of isosorbide dinitrate were 8.4 and 5.9 ng/ml, and those of isosorbide-5-mononitrate were 166.6 and 130.3 ng/ml. At 2 and 7 hours after the second tablet, the concentrations of isosorbide dinitrate were 9.1 and 5.9 ng/ml, and those of isosorbide-5-mononitrate were 224.5 and 148.1 ng/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitrate tolerance in angina therapy. How to avoid it

Tolerance is the attenuation, or loss, of one or several of the effects of organic nitrates after long term administration. All organic nitrate regimens using frequent doses of long-acting nitrates (3 or more times daily), continuous delivery systems [transdermal nitroglycerin (glyceryl trinitrate) patches or continuous intravenous infusions of nitroglycerin] or long-acting (sustained release) preparations will result in partial or complete nitrate tolerance. There are several proposed mechanisms which may contribute to the development of tolerance including activation of neurohormonal mechanisms, plasma volume expansion and depletion of intracellular sulfhydryl cofactors. To avoid tolerance to long term nitrate therapy, regimens should be tailored to provide a 10- to 12-hour nitrate-free interval when possible. This means that antianginal prophylaxis can only be provided by nitrate therapy for some portion of each day, and that some patients will develop an increase in angina in the nitrate-free intervals which will necessitate short term therapy with sublingual nitroglycerin or a similar preparation.

Short and long-acting oral nitrates for stable angina pectoris

Nitroglycerin (NTG) spray and sublingual tablets rapidly relieve an established attack of angina, and their infrequent use is not associated with the development of tolerance. Although, following a suitable nitrate-free interval, the first dose of oral, long-acting nitrates produces significant hemodynamic effects, increases angina free walking, and decreases exercise-induced ischemia, during continued long-term therapy tolerance limits their usefulness. Appropriate dosing regimens of controlled-release formulations of isosorbide dinitrate (ISDN) and controlled-release NTG during long-term therapy have not been established. Use of immediate-release formulation of 15-120 mg of ISDN in a qid regimen lead to a marked reduction in the size and duration of antianginal effects compared to the initial dose. Asymmetric tid therapy with 30 mg of ISDN (7 a.m., 1 p.m., and 6 p.m.) is also associated with the development of partial tolerance and appears to provide antianginal prophylaxis for only a period of 6 hours each day. Asymmetric bid therapy with ISDN at 7 a.m. and noon may give sustained effect but is supported by only a single, small study that did not examine effectiveness after the noon dose in long-term use. Isosorbide-5-mononitrate (IS-5-MN) has been the subject of more recent studies than other nitrates because of attempts to bring a number of products into the U.S. market. IS-5-MN in qid, tid, and standard bid (8 a.m. and 8 p.m.) dosing regimens produce tolerance. Asymmetric regimens of immediate-release IS-5-MN (10 and 20 mg) given bid (once in the morning and again 7 hours later) decrease the development of tolerance compared to symmetric regimens and produce an increased exercise duration after each dose of the day; the 20 mg bid dosing is more effective. Similarly, once-daily 120 and 240 mg controlled-release IS-5-MN does not produce tolerance and gives a sustained increase in daytime exercise duration. Both asymmetric bid immediate-release and once-daily controlled-release IS-5-MN preparations do not produce deterioration in exercise performance prior to the administration of the medication in the morning (i.e., no zero-hour effect). Further studies are needed to establish useful dosing regimens for ISDN, for controlled-release ISDN, and for controlled-release nitroglycerin. None of the dosing regimens of any oral, long-acting nitrate (including IS-5-MN) provide 24 hour antianginal and antiischemic effects.(ABSTRACT TRUNCATED AT 400 WORDS)

Nitrates and angina pectoris

This review discusses the mechanisms of action of the organic nitrates, nitrate tolerance, and the effects of nitrates in patients with stable angina pectoris. The nitrates are prodrugs that enter the vascular smooth muscle, where they are denitrated to form the active agent nitric oxide (NO). NO activates guanylate cyclase, which results in cyclic guanosine monophosphate (cGMP) production and vasodilation as a result of reuptake of calcium by the sarcoplasmic reticulum. NO is identical to endothelium-derived relaxing factor (EDRF), which induces vasodilation, inhibits platelet aggregation, reduces endothelium adhesion, and has anticoagulant and fibrinolytic effects. Thus, the nitrates may be more than vasodilators and, in addition to reducing ischemia, may affect the process of atherosclerosis. The vascular effects of nitrates are attenuated during sustained therapy. Although the basis for the phenomenon of nitrate tolerance is not completely understood, sulfhydryl depletion as well as neurohormonal activation and increased plasma volume may be involved. The administration of N-acetylcysteine, angiotensin-converting enzyme (ACE) inhibitors, or diuretics do not consistently prevent nitrate tolerance. At present, intermittent nitrate therapy is the only way to avoid nitrate tolerance. The intermittent administration of nitrates, however, cannot provide continuous therapeutic benefits, and thus monotherapy with nitrates is not suitable for many patients with stable angina pectoris.

Efficacy of isosorbide mononitrate in angina pectoris

The rapid development of tolerance has limited the applicability of oral and transdermal nitrates in the long-term management of patients with chronic stable angina pectoris. Recent well-controlled trials have demonstrated that asymmetrical, or eccentric, dosing of oral isosorbide mononitrate, in which 20-mg doses are taken at 8 A.M. and 3 P.M., provides at least 12 hours of antianginal coverage. There is no evidence for the development of tolerance with this schedule, which allows for a 17-hour nitrate withdrawal period. Likewise, the asymmetrical 20-mg twice daily regimen has not been associated with the zero-hour effect that has been reported with higher oral doses of isosorbide mononitrate and with intermittent nitroglycerin patch therapy. This approach also avoids the development of a clinical rebound phenomenon, as measured by increased episodes of angina and nitroglycerin consumption, compared with the pretreatment period, during the nitrate-free interval at night and the early hours of the morning.

Role of nitrates in angina pectoris

Nitrates are used extensively for the treatment of angina pectoris. However, continuous therapy with either oral nitrates or nitroglycerin patches leads to rapid development of tolerance, with loss or diminution of antianginal and anti-ischemic effects. The only practical way to avoid the development of tolerance is to use intermittent daily therapy with nitrates. Nitroglycerin patches applied for 10-12 hours during the day increase exercise duration for 8-12 hours, but a rebound increase in anginal attacks during the nitrate-free interval may occur. Oral isosorbide-5-mononitrate, 20 mg twice a day, with the first dose administered in the morning and the second dose 7 hours later, increases exercise duration for at least 12 hours without the development of tolerance to either the morning or afternoon dose. This dosing regimen has been shown not to produce a rebound phenomenon during the periods of low nitrate levels at night and early hours of the morning. Isosorbide dinitrate (30 mg) prescribed at 7 AM and 1 PM does not produce tolerance to the 7 AM dose, but effects of the afternoon dose have not been evaluated. Recent data suggest that isosorbide dinitrate given 3 or 4 times daily produces tolerance and this dosing schedule is inadequate for antianginal prophylaxis. It should be recognized that intermittent oral or patch therapy with nitrates during the day leaves the patient unprotected at night and early hours of the morning. If this is of concern, additional therapy with another class of antianginal agent, preferably a long-acting beta blocker or a long-acting calcium antagonist should be instituted.

Effects of 8:00 a.m. and 2:00 p.m. doses of isosorbide-5-mononitrate during twice-daily therapy in stable angina pectoris

"Trough" plasma concentrations of isosorbide-5-mononitrate (IS-5-MN), an active metabolite of isosorbide dinitrate, of less than 95 ng/ml are considered necessary to prevent development of tolerance to isosorbide dinitrate and IS-5-MN. In a double-blind, crossover, placebo-controlled study, the effects of IS-5-MN during twice daily eccentric therapy were evaluated in 18 patients with reproducible exercise-induced angina who were nitrate responders. In a random order, patients received either placebo or IS-5-MN (20 mg) at 8 a.m. and 2 p.m. for 1 week each. Average trough plasma IS-5-MN concentrations before the 8 a.m. and 2 p.m. doses were 67 and 226 ng/ml, respectively, and increased to 382 and 488 ng/ml 2 hours after the 8 a.m. and 2 p.m. doses, respectively. Despite a more than threefold higher trough plasma IS-5-MN concentration before the 2 p.m. dose than before the 8 a.m. dose, the increase in exercise duration 2 hours after the doses was similar (1.21 minutes [21%] after 8 a.m. dose, and 1.08 minutes [19%] after 2 p.m. dose). These increases in exercise duration after IS-5-MN were significantly (p less than 0.01) greater than those observed after placebo (0.17 minutes [3%] after 8 a.m. dose, and -0.05 minute [-0.5%] after 2 p.m. dose). Reduction in standing systolic blood pressure at 2 hours after the doses was also nearly identical after the 8 a.m. and 2 p.m. doses of IS-5-MN (21 [15%] and 19 [14%] mm Hg, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Nitrate tolerance. How to prevent it or minimize its effect

Continuous therapy with nitrates rapidly produces tolerance along with loss or diminution of circulatory, antianginal, and anti-ischemic effects. Development of tolerance can be avoided by various approaches. In patients with stable angina, intermittent use of nitrates with long nitrate-free intervals, use of transdermal nitroglycerin during the day or oral isosorbide dinitrate or isosorbide-5-mononitrate twice daily in the morning and early afternoon, and intermittent use of nitrates in combination with another class of antianginal agent are appropriate. In patients with unstable angina, continuous therapy with intravenous nitroglycerin is recommended during the acute phase of angina. Despite development of partial tolerance, oral isosorbide dinitrate, 30 to 60 mg four times a day, plus hydralazine may be useful for patients with congestive heart failure who cannot tolerate angiotensin-converting enzyme inhibitors. Concomitant use of sulfhydryl donors or angiotensin-converting enzyme inhibitors, agents that might theoretically prevent nitrate tolerance, is not recommended. Data on these agents are conflicting, and added costs and adverse effects are likely to preclude their use in the future.

Update on nitrate tolerance

1. It is now recognised that nitrate therapy designed to provide effects throughout 24 h each day induces tolerance. Such tolerance may be partial or complete and is associated with diminished haemodynamic and clinical effects. 2. The mechanism of tolerance is not completely understood but it seems to be related to the depletion of reduced sulphydryl groups in vascular smooth muscle and to the activation of counter-regulatory forces. These include elevated plasma catecholamines, arginine vasopressin and plasma renin activity. Activity of the renin-angiotensin system is associated with sodium and water retention and plasma volume expansion. The increase in vasoconstrictor influences and augmented plasma volume could modulate the effect of nitrate-induced vasodilatation.

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.