Short and long-acting oral nitrates for stable angina pectoris

Network pharmacology provides a systematic approach to understanding the treatment of ischemic heart diseases with traditional Chinese medicine

BACKGROUND

The field of network pharmacology showed significant development. The concept of network pharmacology has many similarities to the philosophy of traditional Chinese medicine (TCM), making it suitable to understand the action mechanisms of TCM in treating complex diseases, such as ischemic heart diseases (IHDs).

PURPOSE

This review summarizes the representative applications of network pharmacology in deciphering the mechanism underlying the treatment of IHDs with TCM.

METHODS

In this report, we used "ischemic heart disease" OR "coronary heart disease" OR "coronary artery disease" OR "myocardial ischemia" AND ("network pharmacology" OR "systematic pharmacology") as keywords to search for publications from PubMed, the Web of Science, and Google Scholar databases and then analyzed the representative research reports that summarized and validated the active components and targets network of TCM in improving IHDs to show the advantages and deficiencies of network pharmacology applied in TCM research.

RESULTS

The network pharmacology research indicated that HGF, PGF, MMP3, INSR, PI3K, MAPK1, SRC, VEGF, VEGFR-1, NO, eNOS, NO3, IL-6, TNF-α, and more are the main targets of TCM. Apigenin, 25S-macrostemonoside P, ginsenosides Re, Rb3, Rg3, SheXiang XinTongNing, colchicine, dried ginger-aconite decoction, Suxiao Xintong dropping pills, Ginseng-Danshen drug pair and Shenlian and more are the active ingredients, extracts, and formulations of TCM to ameliorate IHDs. These active compounds, extract, and formulations of TCM treat IHDs by delaying ventricular remodeling, reducing myocardial fibrosis, decreasing reactive oxygen species, regulating myocardial energy metabolism, ameliorating inflammation, mitigating apoptosis, and many other aspects.

CONCLUSIONS

The network pharmacology supplies a novel research exemplification for understanding the treatment of IHDs with TCM. However, the application of network pharmacology in TCM studies is still at a superficial level. By rational combining artificial intelligence technology and network pharmacology, molecular biology, metabolomics, and other advanced theories and technologies, and systematically studying the metabolic process and the network among products, targets, and pathways of TCM from the clinical perspective may be a potential development trend in network pharmacology.

Stable Angina Medical Therapy Management Guidelines: A Critical Review of Guidelines from the European Society of Cardiology and National Institute for Health and Care Excellence

Most patients with stable angina can be managed with lifestyle changes, especially smoking cessation and regular exercise, along with taking antianginal drugs. Randomised controlled trials show that antianginal drugs are equally effective and none of them reduced mortality or the risk of MI, yet guidelines prefer the use of beta-blockers and calcium channel blockers as a first-line treatment. The European Society of Cardiology guidelines for the management of stable coronary artery disease provide classes of recommendation with levels of evidence that are well defined. The National Institute for Health and Care Excellence (NICE) guidelines for the management of stable angina provide guidelines based on cost and effectiveness using the terms first-line and second-line therapy. Both guidelines recommend using low-dose aspirin and statins as disease-modifying agents. The aim of this article is to critically appraise the guidelines’ pharmacological recommendations for managing patients with stable angina.

Nitroglycerin application and coronary arteriogenesis

BACKGROUND

In the presence of a coronary occlusion, pre-existing small collateral vessels (arterioles) develop into much larger arteries (biological bypasses) that have the potential to allow a certain level of perfusion distal to the blockage. Termed arteriogenesis, this phenomenon proceeds via a complex combination of events, with nitric oxide (NO) playing an essential role. The aim of this study was to investigate the effects of supplemental administration of NO donors, i.e., short-acting nitroglycerin (NTG) or slow-release pelleted isosorbide dinitrate (ISDN), on collateral development in a repetitive coronary artery occlusion model in rats.

METHODS

Coronary collateral growth was induced via a repetitive occlusion protocol (ROP) of the left anterior descending coronary artery (LAD) in rats. The primary endpoints were the histological evaluation of rat heart infarct size and ST-segment elevation (ECG-analysis) upon final permanent occlusion of the LAD (experimentally induced myocardial infarction). The effects of NTG or ISDN were also evaluated by administration during 5 days of ROP. We additionally investigated whether concomitant application of NTG can compensate for the anti-arteriogenic effect of acetylsalicylic acid (ASA).

RESULTS

After 5 days of ROP, the mean infarct size and degree of ST-elevation were only slightly lower than those of the SHAM group; however, after 10 days of the protocol, the ROP group displayed significantly less severe infarct damage, indicating enhanced arteriogenesis. Intermittent NTG application greatly decreased the ST-elevation and infarct size. The ISDN also had a positive effect on arteriogenesis, but not to the same extent as the NTG. Administration of ASA increased the infarct severity; however, concomitant dosing with NTG somewhat attenuated this effect.

CONCLUSION

Intermittent treatment with the short-acting NTG decreased the size of an experimentally induced myocardial infarct by promoting coronary collateral development. These new insights are of great relevance for future clinical strategies for the treatment of occlusive vascular diseases.

High sucrose/fat diet and isosorbide mononitrate increase insulin resistance, nitric oxide production and myocardial apoptosis in a hypertensive rat model

The present study aimed to investigate the association between insulin resistance (IR), nitric oxide (NO) production and myocardial apoptosis in a background of coexisting hypertension in a rodent animal model. A hypertensive rat model was established by feeding Wistar and spontaneously hypertensive rats (SHR) with a high sucrose/fat (HSF) diet for 12 weeks, in conjunction with isosorbide mononitrate (ISMN). Increased IR, NO content, apoptotic gene and protein expression, and morphological alterations within rat myocardium were evaluated. Following a total of 12 weeks of feeding with HSF and ISMN resulted in increased IR and NO content within the myocardial tissue of Wistar and SHR rats. HSF and ISMN activated myocardial apoptosis by downregulating the gene transcription and protein expression levels of the anti‑apoptotic B‑cell lymphoma 2 (Bcl‑2), and increasing the pro‑apoptotic Bcl‑2 associated X protein. Apoptosis was demonstrated by DNA fragmentation in terminal deoxynucleotidyl‑transferase‑mediated dUTP nick end labelling assay. In all experiments, the combination of HSF and ISMN was associated with more pronounced effects, indicating the possible synergistic effects. In addition, the correlation analysis in the Wistar rats fed with HSF only, revealed a positive association between NO production and IR. The results of the present study indicated that HSF and ISMN simultaneously increased IR, NO production and myocardial apoptosis in the hypertensive rat model, and may therefore contribute to investigations into the long‑term clinical use of ISMN in hypertensive patients.

The Role of Nitroglycerin and Other Nitrogen Oxides in Cardiovascular Therapeutics

The use of nitroglycerin in the treatment of angina pectoris began not long after its original synthesis in 1847. Since then, the discovery of nitric oxide as a biological effector and better understanding of its roles in vasodilation, cell permeability, platelet function, inflammation, and other vascular processes have advanced our knowledge of the hemodynamic (mostly mediated through vasodilation of capacitance and conductance arteries) and nonhemodynamic effects of organic nitrate therapy, via both nitric oxide-dependent and -independent mechanisms. Nitrates are rapidly absorbed from mucous membranes, the gastrointestinal tract, and the skin; thus, nitroglycerin is available in a number of preparations for delivery via several routes: oral tablets, sublingual tablets, buccal tablets, sublingual spray, transdermal ointment, and transdermal patch, as well as intravenous formulations. Organic nitrates are commonly used in the treatment of cardiovascular disease, but clinical data limit their use mostly to the treatment of angina. They are also used in the treatment of subsets of patients with heart failure and pulmonary hypertension. One major limitation of the use of nitrates is the development of tolerance. Although several agents have been studied for use in the prevention of nitrate tolerance, none are currently recommended owing to a paucity of supportive clinical data. Only 1 method of preventing nitrate tolerance remains widely accepted: the use of a dosing strategy that provides an interval of no or low nitrate exposure during each 24-h period. Nitric oxide's important role in several cardiovascular disease mechanisms continues to drive research toward finding novel ways to affect both endogenous and exogenous sources of this key molecular mediator.

Intermittent Nitrate Use and Risk of Hip Fracture

PURPOSE

Nitrates, commonly used antianginal medications, also have a beneficial effect on bone remodeling and bone density, particularly with intermittent use. However, their effect on fracture risk is not clear. We examined the relation of short-acting nitrate use (proxy for intermittent use) with the risk of hip fracture in a large cohort of older adults with ischemic heart disease.

METHODS

Participants aged 60 years or more with ischemic heart disease and without a history of hip fracture from The Health Improvement Network, an electronic medical records database in the United Kingdom, were included. The association of incident (new) use of short-acting nitrate formulations (nitroglycerin sublingual/spray/ointment or isosorbide dinitrate injection/sprays) with incident (new-onset) hip fracture risk was examined by plotting Kaplan-Maier curves and calculating hazard ratios using Cox proportional hazards regression models. Competing risk by death was analyzed in separate analyses.

RESULTS

Among 14,451 pairs of matched nitrate users and nonusers (mean age, 72 ± 7.6 years, 41% women for each cohort), 573 fractures occurred during follow-up (257 nitrate users; 316 nonusers). Hip fracture risk was 33% lower among short-acting nitrate users compared with nonusers (hazard ratio, 0.67; 95% confidence interval, 0.53-0.85; P = .0008). Competing risk analysis by death did not change effect estimates.

CONCLUSIONS

In this large population-based cohort of older adults with ischemic heart disease, we found a significant reduction in hip fracture risk with the use of short-acting nitrates (intermittent use). Future studies are warranted given the potential for nitrates to be potent, inexpensive, and readily available antiosteoporotic agents.

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.

Role of short-acting nitroglycerin in the management of ischemic heart disease

Nitroglycerin is the oldest and most commonly prescribed short-acting anti-anginal agent; however, despite its long history of therapeutic usage, patient and health care provider education regarding the clinical benefits of the short-acting formulations in patients with angina remains under-appreciated. Nitrates predominantly induce vasodilation in large capacitance blood vessels, increase epicardial coronary arterial diameter and coronary collateral blood flow, and impair platelet aggregation. The potential for the prophylactic effect of short-acting nitrates remains an under-appreciated part of optimal medical therapy to reduce angina and decrease myocardial ischemia, thereby enhancing the quality of life. Short-acting nitroglycerin, administered either as a sublingual tablet or spray, can complement anti-anginal therapy as part of optimal medical therapy in patients with refractory and recurrent angina either with or without myocardial revascularization, and is most commonly used to provide rapid therapeutic relief of acute recurrent angina attacks. When administered prophylactically, both formulations increase angina-free walking time on treadmill testing, abolish or delay ST segment depression, and increase exercise tolerance. The sublingual spray formulation provides several clinical advantages compared to tablet formulations, including a lower incidence of headache and superiority to the sublingual tablet in terms of therapeutic action and time to onset, while the magnitude and duration of vasodilatory action appears to be comparable. Furthermore, the sublingual spray formulation may be advantageous to tablet preparations in patients with dry mouth. This review discusses the efficacy and utility of short-acting nitroglycerin (sublingual spray and tablet) therapy for both preventing and aborting an acute angina attack, thereby leading to an improved quality of life.

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.

A randomized, double-blind, placebo-controlled, crossover, dose-ranging multicenter study to determine the effect of sublingual nitroglycerin spray on exercise capacity in patients with chronic stable angina

BACKGROUND

Sublingual nitroglycerin increases exercise duration in patients with stable angina. Brief results from this study were published previously in German. Here, we more fully describe the study methodology, patient characteristics, and detailed results.

METHODS

This double-blind, crossover study enrolled 51 patients with stable angina. Patients were randomized to 1 of 5 treatment sequences and were administered placebo or nitroglycerin spray (0.2 mg, 0.4 mg, 0.8 mg, or 1.6 mg). Patients carried out 1 control exercise tolerance test (ETT) and 1 investigational ETT at each visit.

RESULTS

Dose-dependent increases in time to onset of angina, time to onset of moderate angina, and the occurrence of a minimum 1.0-mm ST-segment depression were seen following administration of nitroglycerin spray.

CONCLUSIONS

These results support the use of sublingual nitroglycerin spray in patients with stable angina who are being managed with medical therapy and in patients who have persistent angina post-revascularization.

Side effects of using nitrates to treat heart failure and the acute coronary syndromes, unstable angina and acute myocardial infarction

Nitrates are potent venous dilators and anti-ischemic agents. They are widely used for the relief of chest pain and pulmonary congestion in patients with acute coronary syndromes and heart failure. Nitrates, however, do not reduce mortality in patients with acute coronary syndromes. Combination of nitrates and hydralazine when given in addition to beta-blockers and angiotensin-converting enzyme (ACE) inhibitors reduce mortality and heart failure hospitalizations in patients with heart failure due to left ventricular systolic dysfunction who are of African-American origin. Side effects during nitrate therapy are common but are less well described in the literature compared with the reported side effects in patients with stable angina pectoris. The reported incidence of side effects varies highly among different studies and among various disease states. Headache is the most commonly reported side effect with an incidence of 12% in acute heart failure, 41-73% in chronic heart failure, 3-19% in unstable angina and 2-26% in acute myocardial infarction. The reported incidence of hypotension also differs: 5-10% in acute heart failure, 20% in chronic heart failure, 9% in unstable angina and < 1-48% in acute myocardial infarction, with the incidence being much higher with concomitant nitrate therapy plus angiotensin-converting enzyme inhibitors. Reported incidence of dizziness is as low as 1% in patients with acute myocardial infarction to as high as 29% in patients with heart failure. Severe headaches and/or symptomatic hypotension may necessitate discontinuation of nitrate therapy. Severe life threatening hypotension or even death may occur when nitrates are used in patients with acute inferior myocardial infarction associated with right ventricular dysfunction or infarction, or with concomitant use of phosphodiesterase-5 inhibitors or N-acetylcysteine. Despite the disturbing observational reports in the literature that continuous and prolonged use of nitrates may lead to increased mortality and recurrent myocardial infarction in patients with stable coronary artery disease, no such adverse effects of nitrates have been reported in the large randomized trials in patients with acute myocardial infarction or chronic heart failure.

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.

The effects of organic nitrates on osteoporosis: a randomized controlled trial [ISRCTN94484747]

Background

Osteoporotic fractures are common and are associated with increased morbidity, mortality and health care costs. The most effective way to moderate increases in health care costs and the sickness and premature death associated with osteoporotic fractures, is to prevent osteoporosis. Several lines of evidence suggest that nitrates, drugs typically prescribed for the treatment of angina, may be effective in preventing postmenopausal osteoporosis.

Methods

We have designed a multicentre randomized controlled trial to determine the effects of nitrates on bone. The trial consists of two studies. The objective of the first study is to determine whether isosorbide mononitrate at 20 mg/day or nitroglycerin ointment at 15 mg/day leads to fewer headaches. The nitrate that is best tolerated will be used in a second study with one main objective: To determine if postmenopausal women with a T-score at the lumbar spine (L1 to L4) between 0 and -2.0 randomized to two years of treatment with intermittent nitrates have a greater increase in spine bone mineral density as compared to women randomized to placebo.

We hypothesize that: 1. Women will report fewer headaches when they are randomized to intermittent nitroglycerin ointment at 15 mg/day compared to intermittent oral isosorbide mononitrate at 20 mg/day, and, 2. After two years, women randomized to intermittent nitrates will have a greater percent increase in lumbar spine bone mineral density compared with women randomized to placebo.

Discussion

We have completed our pilot study and found that transdermal nitroglycerin was associated with fewer headaches than oral isosorbide mononitrate. We are currently recruiting patients for our second main study.

Current medical management of chronic stable angina

Severe atherosclerotic narrowing of one or more coronary arteries is responsible for myocardial ischemia and angina pectoris in most patients with stable angina. The coronary arteries of patients with stable angina also contain many more non-obstructive plaques, which are prone to rupture resulting in acute coronary syndrome (unstable angina, myocardial infarction, sudden ischemic death). Therefore, the medical management must use strategies which not only relieve symptoms and prolong angina free walking but also reduce the incidence of adverse clinical outcomes. Whether any of the approved antianginal drugs, nitrates, beta-blockers, and calcium channel blockers reduce the incidence of adverse clinical outcomes in patients with stable angina has not been studied to date. Published data shows that percutaneous coronary revascularization procedures and coronary bypass surgery are effective in relieving angina but these procedures do not reduce mortality or the incidence of myocardial infarction compared to anti-anginal drug therapy. From the available data, an initial trial of medical treatment with anti-anginal drugs and strategies to reduce adverse clinical outcomes (smoking cessation, daily aspirin, treatment of dyslipidemias and hypertension) is indicated in most patients with stable angina pectoris. The initial choice of drug will depend on the presence or absence of comorbid conditions. Patients who do not respond to medical therapy or do not wish to take anti-anginal drugs and whose life style is limited because of anginal symptoms should be offered percutaneous revascularization procedures with or without stent placement or coronary bypass surgery. New drug-coated stents hold promise but long-term data and large-scale trials assessing the continued long-term improvement in symptoms and reduction of adverse outcomes is needed before offering such devices to all patients with stable angina. Newer medical therapies such as metabolic modulators and sinus rate lowering drugs also hold promise but need further evaluation. Patients who have refractory angina despite optimal medical therapy and are not candidates for revascularization procedures may be candidates for some new techniques of enhanced external Counterpulsation, Spinal Cord Stimulation, sympathectomy or direct transmyocardial revascularization. The usefulness of these techniques, however, needs to be confirmed in large randomized trials.

Tolerance to nitroglycerin induced by isosorbide-5-mononitrate infusion in vivo

We examined the development of tolerance to nitroglycerin (glyceryl trinitrate; GTN) in the rat when isosorbide-5-mononitrate (ISMN) or GTN was continuously infused. Under pentobarbital anesthesia (60 mg/kg, i.p.), mean arterial blood pressure was measured via the left common carotid artery. Bolus injection of ISMN (0.25-250 mg/kg) and GTN (0.25 microg/kg-2.5 mg/kg) was made into the right external jugular vein. ISMN (2.5 mg/h/rat for 7 d), GTN (1.3 microg/h/rat for 7 d), or GTN (0.2 mg/h/rat for 3 d) was infused continuously using an osmotic pump embedded subcutaneously. Bolus injection of ISMN and GTN decreased arterial blood pressure in a dose-dependent manner. The hypotensive effect of ISMN was 2000 times less potent than that of GTN. The GTN-induced hypotensive effect was not affected after continuous infusion of ISMN, whereas it was attenuated after continuous infusion of GTN at either dose. Chronic treatment with ISMN does not induce GTN tolerance as easily as treatment with GTN.

Managed substitution of modified release nitrates with an asymmetric dosing regimen

BACKGROUND

Orally administered modified release organic nitrates are used commonly in the prophylaxis of myocardial ischaemia, although little evidence indicates a clinically superior response compared with standard formulated preparations administered symmetrically.

AIM

To investigate the clinical success of transfer of suitable patients from MR to SF nitrates.

METHOD

Suitable candidates for therapeutic substitution, assessed by a pharmacist, completed a baseline study to estimate frequency and timing of chest pain, the number of rescue doses of sublingual nitrates required, together with an assessment of adverse effects experienced. Following substitution to an eccentric dosing schedule, a further one month's assessment of chest pain frequency, rescue nitrate use and adverse effects was recorded and compared with baseline.

RESULTS

Twelve (37.5%) patients from a possible 32 candidates were invited to complete a baseline symptoms and adverse event diary. Eight patients entered the study phase (66.7% of the 12 included in the baseline phase of the study). These candidates showed no evidence of loss of control of chest pain symptoms, 3.5 +/- 1.16 (mean +/- standard error of mean) episodes/patient/28 days compared with 1.9 +/- 0.96 episodes/patient/28 days during the test phase (P > 0.05). Similarly, there was no difference in the number of doses of rescue nitrates required when the trial phase (2.6 +/- 1.63 doses/patient/28 days) was compared with the control (2.0 +/- 1.31 doses/patient/28 days, P > 0.05). There was no evidence of an increased incidence of adverse effects during the trial period of the study.

CONCLUSION

This small study suggests that, if selected carefully, therapeutic substitution of MR oral nitrates can be managed successfully without apparent risk of loss of symptom control or increased incidence of adverse effects.

Sustained reduction of exercise perfusion defect extent and severity with isosorbide mononitrate (Imdur) as demonstrated by means of technetium 99m sestamibi

BACKGROUND

The impact of long-acting nitrates on the extent and severity of stress-induced myocardial ischemia is not well described, especially after long-term treatment.

METHODS

Forty patients with chronic stable angina and reversible ischemia on an exercise stress myocardial perfusion single photon emission computed tomography (ex-SPECT) were prospectively studied in a 6-week period. At baseline, rest thallium-201/exercise stress technetium 99m sestamibi SPECT was performed, followed by treatment with extended-release isosorbide 5-mononitrate (5-ISMN, Imdur). Follow-up ex-SPECT was performed 5 days and 6 weeks after the initiation of therapy with extended-release 5-ISMN. The exercise treadmill testing (ETT) protocol and exercise duration of the follow-up studies were the same as that of the baseline ETT. Defect extent and severity were analyzed both by means of an automated quantitative method, with CEqual software, and visually, with a 20-segment scoring system (which was also used to derive a summed stress score [SSS]).

RESULTS

In the 6-week study period, significant reductions occurred in both the extent and the severity of exercise-induced ischemia by means of quantitative SPECT (13.8% [P<.0003] and 12.7% [P<.0003], respectively). There was no significant change in these variables between stages 2 (day 5) and 3 (6 weeks), indicating no development of tolerance to the nitrate effect. Similar reductions were noted by means of the visual analysis (SSS reduction of 13.0% [P<.002]) in the entire study period.

CONCLUSIONS

Patients with chronic-stable-angina treated with a long-acting nitrate demonstrate improvement in myocardial perfusion defect extent and severity in an extended period by means of both visual and quantitative analysis of sequential exercise testing to the same rate-pressure product end point.

Treatment of stable angina

Severe atherosclerotic narrowing of one or more coronary arteries is responsible for myocardial ischemia and angina pectoris in most patients with stable angina pectoris. The coronary arteries of patients with stable angina also contain many nonobstructive plaques, which are prone to fissures or rupture resulting in presentation of acute coronary syndromes (unstable angina, myocardial infarction, sudden ischemic death). In addition to symptomatic relief of symptoms and an increase in angina-free walking time with antianginal drugs or revascularization procedures, the recent emphasis of treatment has been to reduce adverse clinical outcomes (coronary death and myocardial infarction). The role of smoking cessation, aspirin, treatment of elevated lipids, and treatment of high blood pressure in all patients and of beta-blockers and angiotensin-converting enzyme inhibitors in patients with diminished systolic left ventricular systolic function in reducing adverse outcomes has been well established. What is unknown, however, is whether any anti-anginal drugs (beta-blockers, long-acting nitrates, calcium channel blockers) effect adverse outcomes in patients with stable angina pectoris. Recent trials evaluated the usefulness of suppression of ambulatory ischemia in patients with stable angina pectoris, but it remains to be established whether suppression of ambulatory myocardial ischemia with antianginal agents or revascularization therapy is superior to pharmacologic therapy targeting symptom relief. Patients who have refractory angina despite optimal medical treatment and are not candidates for revascularization procedures may be candidates for newer techniques of transmyocardial revascularization, enhanced external counterpulsation, spinal cord stimulation, or sympathectomy. The usefulness of these techniques, however, needs to be confirmed in large randomized clinical trials.

Factors associated with the use of various medications amongst patients with severe coronary artery disease. SECOR/SBU Project Group

AIM

To describe variations by age, sex, symptom severity and hospital region in the use of various medications amongst patients with stable angina pectoris who are candidates for coronary revascularization.

PATIENTS

Patients (n = 2030) with chronic stable angina pectoris participating in a national survey evaluating the appropriateness of the use of percutaneous transluminal coronary angioplasty (PTCA) and coronary artery bypass grafting (CABG).

METHODS

As part of a national study of the appropriateness of coronary revascularization, data were prospectively collected on patients referred for consideration of coronary revascularization to seven of the eight public Swedish heart centres that performed approximately 92% of all bypass operations in Sweden in 1994.

RESULTS

Amongst all patients 76% were treated with beta blockers, 41% with calcium antagonists and 71% with long-acting nitrates and 70% were treated with at least two of these three drugs. Eighty-two per cent of the patients used aspirin and 14% lipid-lowering drugs. According to logistic regression analysis, with medication as the dependent variable and independent variables of age, sex, angina functional class, findings at exercise test, history of various diseases and region in Sweden where the investigation took place, the most consistent factor explaining the use of various medications was found to be geographical region. A previous history of acute myocardial infarction (AMI) was also associated with the use of all drugs and age was associated with all with the exception of beta blockers. Sex was not an independent factor explaining the use of any of the drugs.

CONCLUSION

In a national survey including patients with stable angina pectoris who are potential candidates for coronary revascularization, the most important predictor for the use of various medications was the geographical region in which the investigation took place.

Isosorbide 5-mononitrate: a review of a sustained-release formulation (Imdur) in stable angina pectoris

Imdur (IMD) is a sustained-release isosorbide 5-mononitrate preparation for the treatment of chronic stable angina pectoris. Controlled medication release is achieved using the Durules principle of insoluble matrix embedding. Data from randomised double-blind trials show that IMD 60 mg once daily (the most widely studied dosage) has significant antianginal and anti-ischaemic effects compared with placebo after 2 weeks' treatment. Efficacy was generally observed approximately 1 to 12 hours after administration, indicating that once-daily administration in the morning will provide effective prophylaxis of symptoms throughout the day. Improvements from baseline are generally maintained during IMD repeated treatment. There was no evidence of classical tolerance to IMD 30 to 240 mg/day in a large well designed study. Although improvements from baseline were maintained over 6 weeks with IMD 30 or 60 mg/day, statistical significance versus placebo was eventually lost because of improved performance in the placebo group. IMD 120 or 240 mg/day were more effective than placebo after 6 weeks. Studies lasting up to 2 weeks found no evidence of tolerance to IMD 60 mg/day. In comparative trials lasting approximately 2 weeks, IMD 60 mg once daily was more effective than isosorbide dinitrate 30 mg 4 times daily and similar to or better than isosorbide dinitrate 20 mg 3 times daily. Preliminary data show that IMD 60 mg once daily has similar efficacy to diltiazem 60 mg 3 times daily and is at least as effective as certain other sustained-release isosorbide 5-mononitrate preparations. There is no evidence for rebound worsening of ischaemia 24 hours after IMD administration. Abrupt discontinuation during long term IMD treatment may exacerbate anginal symptoms. In general, IMD is well tolerated. The most frequently reported adverse event, headache, is usually mild to moderate, improves with long term therapy and rarely leads to treatment withdrawal. Patient compliance is better with once-daily administration of IMD than with twice-daily administration of conventional isosorbide 5-mononitrate.

CONCLUSIONS

In patients with chronic stable angina, IMD provides effective antianginal prophylaxis for up to 12 hours and does not seem to be associated with rebound phenomena at the end of the dosage interval. Improvements from baseline are maintained during repeated administration, although loss of statistically significant superiority over placebo was evident during 6 weeks' treatment with IMD < or =60 mg/day in 1 study. Further evaluation of comparative efficacy (particularly with respect to other sustained-release preparations) and long term effects would be beneficial. Nevertheless, the available data suggest that IMD is a useful and convenient agent for the treatment of patients with chronic stable angina pectoris.

Comparison of multiple-dose and once-daily nitrate therapy in 1212 patients with stable angina pectoris: effects on quality of life indices. Dutch Mononitrate Quality of Life (DUMQOL) Study Group

BACKGROUND

Nitrates, although important for the management of anginal symptoms, produce significant side effects. Little is known about their net effects on health-related, quality-of-life indices.

METHODS

In a self-controlled, 6-month study, the effects on symptoms and quality of life of multiple-dose and once-daily nitrate therapy were evaluated in 1212 patients with stable angina pectoris. Quality of life was assessed by a test battery based on the exercise-tolerance index of Wiklund, the psychological well-being index of Dupuy, and the Short Form 36 questionnaire of Stewart. The internal consistency and reliability of the multi-item scales were estimated by Cronbach's alpha coefficients.

RESULTS

The effects of the two treatment regimens on pain index and number of additional sublingual nitrate tablets required were not different. However, based on the New York Heart Association (NYHA) angina classification, patients improved better on the once-daily than on the multiple-dose regimen: by > 1 category in 281 vs 62 of the patients (P < 0.0001); mobility and psychological distress indices also improved (P = 0.006, and P = 0.007).

CONCLUSIONS

Once-daily nitrate therapy not only provides a better NYHA angina classification than multiple-dose therapy does, but also provides a better quality of life as estimated by improvement of mobility and distress indices, the most important indicators of quality of life in this category of patients.

Achieving sustained improvement in myocardial perfusion: role of isosorbide mononitrate

The efficacy of antianginal agents in the treatment of patients with chronic stable angina has traditionally been evaluated by performance measures, such as the exercise treadmill test (ETT). Although reliable and reproducible, ETT is not a sensitive measure of changes in myocardial ischemia. The effects of antianginal agents on coronary blood flow and myocardial perfusion have been less frequently studied. Angiographic studies have demonstrated that nitrates may operate by preferentially directing blood flow to ischemic regions of the myocardium. These investigations have been limited, however, by the invasive nature of the evaluation. Measurements of regional myocardial perfusion may also be made with noninvasive tests. Both quantitative single-photon emission computed tomography (SPECT) and positron emission tomography (PET) have been employed, but few studies have used these techniques to assess the effects of antianginal drugs (in general) and nitrates (in particular) on changes in reversible myocardial perfusion defects. Studies that have evaluated the direct effects of nitrate treatment on coronary blood flow and myocardial perfusion defects in patients with chronic stable angina are reviewed, and preliminary data from a study of the effects of long-term nitrate treatment on myocardial perfusion are discussed.

Management of patients with chronic stable angina at low risk for serious cardiac events

Successful management of the patient with chronic stable angina requires correct stratification by assessing the risk of future coronary events. Patients at low risk for such events have a relatively good prognosis; revascularization procedures (balloon angioplasty or surgery) offer no benefit over medical management. Such patients should be offered medical therapy as their first option. The goals in management of chronic stable angina are (1) treatment of other conditions that may worsen angina; (2) treatment with aspirin and modification of risk factors for coronary artery disease (CAD) to improve outcome; and (3) effective relief of anginal symptoms. Most patients with stable angina will have CAD. It is well established that treatment with aspirin and modification of risk factors for CAD are beneficial in reducing cardiovascular mortality and morbidity. Blood pressure reduction, lowering of blood cholesterol level, and smoking cessation are interventions of proven value and appear to correct defects (at least partially) in the endothelial function of the coronary blood vessels. Other interventions that are helpful are estrogen replacement treatment in postmenopausal women, and low-dose aspirin therapy-which is recommended for all patients who can tolerate it. For controlling symptoms and improving angina-free walking time, nitrates, beta blockers, and calcium channel antagonists are efficacious as first-line monotherapy for chronic stable angina in this group of patients. Nitrates may be of special use in patients with impaired left ventricular function, overt congestive heart failure, intermittent coronary vasoconstriction, or coronary artery spasm. In patients with concomitant hypertension or supraventricular tachycardia, beta blockers are helpful. Calcium channel antagonists may be useful in patients with chronic obstructive pulmonary disease, peripheral vascular disease, or hypertension. When optimal monotherapy with a given class of drug fails to control symptoms, alternative monotherapy with a different class of agent should be tried before combination therapy. Combination therapy with 2 or 3 agents is not always superior to optimal monotherapy. Patients who fail to respond to adequate medical therapy should be considered for a revascularization procedure.

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.

Intermittent or continuous transdermal nitroglycerin: still an issue, or is the case closed?

After a decade of controversy and debate, many experts have now concluded that continuous nitroglycerin patch treatment leads to complete tolerance development and therefore cannot be recommended for any angina patient. This conclusion is largely based on the disappointing results of the large Transdermal Nitroglycerin Cooperative Study, in which continuous patch treatment in doses of 15-105 mg daily failed to increase exercise duration more than placebo after 2 and 8 weeks of treatment. However, other well-designed studies recently reported maintained efficacy during continuous treatment, and the differences in results has remained unexplained. The disagreeing data may be better understood if certain facts are considered: (1) The cooperative study tested a patient population with a very low first-dose treatment response--only 34 seconds (or 10-12%) improvement compared with placebo. At the end of the study, 25% of the patients terminated exercise for reasons other than angina, and a reduced nitrate responsiveness had developed, even in the placebo group. (2) Patients who demonstrate a large first-dose nitrate responsiveness tend to be less susceptible to tolerance development. (3) Even during continuous therapy, maintained efficacy is often observed in exercise tests done 2-5 hours after patch renewal, while typically no effect is seen at the end of the application period. Attenuation of the initial effects is seen with all long-acting nitrate treatment regimens, but the degree of tolerance varies with the patient population, the efficacy parameter (exercise test vs. attack counts), the timing of the efficacy test, the patch dose, and whether or not nitrate-free (-low) intervals are used. In general, intermittent patch therapy is superior to continuous therapy in improving exercise duration, but even continuous therapy may retain some effect. Rebound phenomena do occur but are clinically relevant only in a minority of the patients. Rebound phenomena are not a problem during continuous therapy, which therefore may be of value in patients with frequent and/or nocturnal angina attacks. Patients experiencing angina during exercise only and with low first-dose effects are likely to benefit more from intermittent therapy. Doses of 0.6-0.8 mg/hr (15-20 mg/24 hr) are usually optimal, and the efficacy is comparable with that observed after oral nitrates.