Oral nitroglycerin as a prophylactic antianginal drug: clinical, physiologic, and statistical evidence of efficacy based on a three-phase experimental design

Chemical Strategies Toward Prodrugs and Fluorescent Probes for Gasotransmitters

Three gaseous molecules are widely accepted as important gasotransmitters in mammalian cells, namely NO, CO and H2S. Due to the pharmacological effects observed in preclinical studies, these three gasotransmitters represent promising drug candidates for clinical translation. Fluorescent probes of the gasotransmitters are also in high demand; however, the mechanisms of actions or the roles played by gasotransmitters under both physiological and pathological conditions remain to be answered. In order to bring these challenges to the attention of both chemists and biologists working in this field, we herein summarize the chemical strategies used for the design of both probes and prodrugs of these three gasotransmitters.

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.

Nitrate therapy today

A review of nitrate therapy including a short summary of their physiological effects is presented. Both cardiac and non-cardiac indications are reviewed including esophageal spasm, spasm of bile ducts and urinary tract, Raynaud's disease, pulmonary hypertensive disorders, portal hypertension, bronchial asthma, and effect on arrhythmias.

Assessment of ischemic changes by ambulatory ECG-monitoring: comparison with 12-lead ECG during exercise testing

The accuracy of commercially available ambulatory electrocardiographic monitoring (AEM) systems for reproducing ischemic changes has been questioned. Since these systems are widely used for evaluation of ST-segment changes, both for prognostic purposes and for assessment of the efficacy of antiischemic drugs, such doubts must be clarified. For this purpose, we recorded electrocardiograms (ECGs) during exercise testing, using split leads, simultaneously with a 12-lead electrocardiograph and with the Marquette AEM recorder. We studied 29 patients with proven coronary artery disease and positive exercise tests and 19 individuals with low likelihood of coronary artery disease and negative stress tests. All 29 patients who had ST-segment depression during exercise as recorded on the 12-lead ECG had ST-segment depression in at least one of the three AEM leads (resembling the V5, V3, and aVF leads of the 12-lead system). The maximal degree of ST-segment depression with AEM was similar to 12-lead ECG (2.3 mm and 2.1 mm, respectively). The best lead for ischemia detection with AEM was the V5 type, which detected ischemic changes in 26 of the 29 patients, while the 12-lead V5 detected ischemia in 24 patients. The inferior AEM lead detected ischemia in only 4 patients, while the aVF lead of the 12-lead ECG detected ischemia in 23 patients. Of the 19 patients with negative exercise tests only 1 patient had a 1-mm ST-segment depression on AEM. Thus, of the 48 patients studied, similar responses were observed in 47. The results of indicate that the Marquette AEM system is as accurate as the 12-lead ECG in detecting ischemic changes and in assessing their severity.

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.

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)

Effects of digitalis, anti-anginal drugs and arterial hypertension on the relationships between exercise ECG and angiocardiographic variables and on the diagnostic accuracy of exercise ECG in patients with coronary heart disease

We have previously found a statistically significant correlation between some exercise ECG variables and angiocardiographic scores used to evaluate the extent and type of coronary heart disease (CHD). In the present study we examined the effects of digitalis, beta-adrenergic blockers, slow release nitrates, calcium channel blockers, presence of arterial hypertension (AHT), and angiocardiographic changes on the exercise ECG variables. The effects of drugs and AHT were small as compared to the effects of the angiocardiographically detected pathological changes caused by the CHD. Sensitivity and specificity of the exercise ECG ST criteria in identifying patients with an angiocardiographic criterion indicating coronary insufficiency were not much different in the whole group and in the subsets with AHT or medication with digitalis and anti-anginal drugs.

Controlled-release isosorbide dinitrate pellets. Part II: In vivo studies

Isosorbide dinitrate (ISDN) capsules containing 20.0 and 40.0 mg of the drug (reported earlier in Part I of this series) were evaluated in vivo in eight healthy volunteers in a double-blind study with marketed sustained-release preparations containing 20.0 and 40.0 mg of ISDN. The results were normalized by administering placebo and four conventional ISDN tablets, each containing 5.0 mg of ISDN, to the same group of volunteers in a separate study. The blood pressure of the volunteers was monitored for 8 h. The results indicate that the capsules prepared in the laboratory with the new formulation gave controlled release when compared with the respective marketed SR product.

Simultaneous pharmacodynamic modeling of the non-steady-state effects of three oral doses of 1,3-glyceryl dinitrate upon blood pressure in healthy volunteers

The organic nitrate 1,3-glyceryl dinitrate (1,3-GDN) is one of the primary dinitrate metabolites of the antianginal agent nitroglycerin (GTN). Investigational New Drug Approval was sought to administer oral solution doses of 1,3-GDN to a small number (n = 3) of healthy volunteers; each subject receiving three doses at 1.2, 2.4, and 3.6 mg. With volunteers confined to a semirecumbent posture for the duration of each treatment (4-hr period postdose), diastolic blood pressure (DBP) was recorded and plasma samples collected for 1,3-GDN concentration analysis. Appreciable concentration-related decreases in DBP were observed, with maximal decreases from predose baseline values approximating 11 to 25 mm Hg. For each subject parametric pharmacodynamic modeling was performed with simultaneous analysis utilizing the DBP vs. time data from all three doses; an inhibitory Emax pharmacodynamic model was adopted. The temporal relationship between plasma 1,3-GDN concentrations and DBP displayed rapid equilibration. For subjects 1, 2 and 3, respectively, Emax was predicted as 12.9, 23.4, and 29.7 mm Hg, representing 21.5, 31.6, and 39.5% decreases in DBP from predose baseline values; plasma concentrations at half Emax (C50) were 2.75, 2.43, and 5.93 micrograms/L. Utilizing pharmacokinetic-pharmacodynamic modeling, 1,3-GDN plasma concentrations appear to relate to a systemic "effect measure" that is mechanistically representative of the therapeutic actions of organic nitrates as peripheral vasodilators. The establishment of a GDN plasma concentration-effect relationship together with the relatively high plasma levels of GDN achieved following GTN dosing supports the hypothesis that the GDNs contribute significantly to the hemodynamic effect observed with GTN.

Pharmacokinetics of nitroglycerin and its metabolites after administration of sustained-release tablets

Nitroglycerin was administered to eight healthy volunteers in the form of sublingual tablets, oral sustained-release tablets, and an oral solution. Blood samples were collected for measurement of nitroglycerin and its two isomeric glyceryl dinitrate metabolites. Blood pressure and pulse rate were monitored; subjective evaluations of headache, dizziness, facial flushing, skin irritation, and gastrointestinal upset were made. Nitroglycerin itself was virtually undetectable after the solution and tablet preparations; the metabolites were consistently detectable from a few minutes after dosing to 24 h later. Mean total (nitroglycerin plus metabolite) concentrations were comparable in the 15 min following sublingual administration, and the 8 h following tablet administration. The relative bioavailability of the tablets in comparison with the oral solution was 70 per cent based on metabolite concentrations. Nitroglycerin sustained-release tablets appear to exert their beneficial effects in the prolonged prophylaxis of angina through active metabolites.

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.

Variable glyceryl dinitrate formation following infusions of glyceryl trinitrate at different vascular sites in the rat

The availability of glyceryl trinitrate (GTN) and the differential formation of dinitrate metabolites (GDNs) in various organs as a function of routes of administration were investigated in the rat. GTN was infused at 2.0 micrograms/min via the left femoral vein (LFV), left external jugular vein (LJV), left femoral artery (LFA), and hepatic portal vein (HPV). Blood concentrations of GTN and GDNs were measured in femoral arterial samples. Different infusions yielded GTN steady-state concentrations in the following rank order: LJV greater than or equal to LFV greater than LFA greater than or equal to HPV. Furthermore, the GDN formation ratios (1,2-GDN/1,3-GDN) are different: LFV greater than LJV greater than LFA greater than HPV. The availabilities of GTN through the leg, vein, and liver were derived. GTN is significantly extracted and metabolized in these organs, and the leg and the vein prefer 1,2-GDN formation, while the liver forms 1,3-GDN predominantly.

Nitroglycerin absorption from transdermal systems: formulation effects and metabolite concentrations

We recently compared plasma concentrations of nitroglycerin and its two dinitrate metabolites in 16 healthy male subjects after application of two controlled-release transdermal formulations of the drug. Analysis of the resulting plasma concentration-time curves indicated that the two formulations did not produce equivalent concentrations of parent drug or either of the dinitrate metabolites during the initial period of dosing. In addition, both formulations produced concentrations of the two dinitrate metabolites that exceeded the concentration of the parent drug by severalfold. Even if the pharmacologic effect of the dinitrate metabolites is low compared to that of nitroglycerin, these higher concentrations may contribute to the effect of nitroglycerin. Scrutiny of the ratio of 1,2-glyceryl dinitrate to 1,3-glyceryl dinitrate in the 16 subjects confirmed previous observations that preferential formation of the 1,2-glycerol dinitrate metabolite may occur depending on the route of administration. This ratio may thus be indicative of the bioavailability of nitroglycerin following transdermal application. Additional data suggesting racial differences in nitroglycerin absorption after transdermal application are presented.

Pharmacokinetic studies of the nitroglycerin metabolites, 1,2- and 1,3- glyceryl dinitrates, in the rat

1,2- and 1,3-glyceryl dinitrates (1,2-GDN and 1,3-GDN) are the primary metabolites of glyceryl trinitrate, a commonly used anti-anginal agent. The goal of this study was to examine the pharmacokinetic properties of these metabolites in rats. Sprague-Dawley rats were infused intravenously with 0.25 or 2.0 micrograms min-1 of either 1,2- or 1,3-GDN for 70 min, during which steady state blood concentrations were achieved. Post-infusion blood samples were collected for 30 min. 1,2-GDN was found to possess slightly higher clearance (32.3 vs 20.8 ml min-1 kg-1) and volume of distribution (695 vs 454 ml kg-1) than 1,3-GDN; however, the two metabolites exhibited similar mean residence times (22.0 vs 21.8 min). Upon an 8-fold increase in the infusion rate, the pharmacokinetic parameters were not significantly altered for either 1,2- or 1,3-GDN. When each GDN was co-infused with an 8-fold higher dose of the other GDN, there were also no significant changes in the parameters.

Dissociation of exercise tolerance and total myocardial ischemic burden in chronic stable angina pectoris

Exercise treadmill tests and ambulatory monitoring were used in a double-blind, placebo-controlled, double-dummy crossover comparison of nifedipine (10 mg, 3 times daily) and transdermal nitroglycerin (15 mg). All patients (n = 20) had chronic stable angina with symptomatic and silent events. All patients had 3 episodes of angina/week and 3 episodes of ischemia/24 hr. The protocol was made up of 2 weeks of placebo followed by 2 weeks of active drug, then crossed over for 2 weeks of placebo followed by the other active drug. At the end of each 2-week period, patients had ambulatory monitoring and exercise treadmill testing. All ambulatory monitoring reports were read blind and entered into an independent data base. The results were the following: on transdermal nitroglycerin, the duration of ischemia decreased by 57% from 140 min/24 hr to 60 min/24 hr (p = 0.0054). The exercise time increased by 5.5% from 4.8 to 5.0 minutes (p = 0.16). With nifedipine, the duration of ischemia decreased by 22% from 175 min/24 hr to 137 min/24 hr (p = 0.16). The exercise tolerance time increased by 13% from 4.5 to 5.0 minutes (p = 0.0264). Nifedipine increased exercise time without altering total ischemic time, while transdermal nitroglycerin decreased total ischemic time without increasing exercise time. Thus, changes in exercise time do not necessarily predict changes in total ischemic time.

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.

Pharmacokinetics of nitroglycerin and metabolites in humans following oral dosing

Single dose oral nitroglycerin (GTN) was administered to six healthy subjects as 6.5, 9.0, and 13.0 mg aqueous solutions in sequential study phases to characterize the oral pharmacokinetics of GTN and the dinitrate metabolites. Blood samples were collected periodically up to 10 h. Plasma concentrations of GTN were measurable in some subjects up to 1/2 and 1 h, respectively, after the 9.0 and 13.0 mg dose. The mean GTN Cmax values of the three solution doses were 0.28, 0.78, and 0.42 ng ml-1 in ascending dosage. The erratic nature of GTN plasma profiles prevented meaningful pharmacokinetic analysis, although tmax was consistently 5 min. In all three treatments, both GTN metabolites (1,2- and 1,3-glyceryldinitrates, GDNs) peaked at about 20 min, followed by a distributive phase and a log-linear decline in concentrations. Terminal half-lives for both GDNs were approximately 50 min in all three doses. The plasma concentrations of the metabolites were higher than nitroglycerin with 1,2-GDN exhibiting the highest overall profile.

Oral nitroglycerin in angina pectoris--evaluation of effect by computerized exercise testing using two different doses

The antianginal effects of sustained-released oral nitroglycerin were evaluated in patients with chronic stable angina using a double-blind randomized protocol. Nineteen patients were inducted into the trial and 17 of these completed the study. Two doses of oral nitroglycerin were used; 2.6 mg and 6.5 mg given three times daily for a period of 2 weeks, the patients crossing over to the alternative dose at the end of each period. Evaluation of effect was carried out 2 hours after the morning dose using graded treadmill exercise testing with on-line computer analysis of the electrocardiogram (EKG) (CASE, Marquette Electronics, Inc.). Various exercise parameters were measured and the results compared to placebo values and between the two dosages. The aim was to demonstrate an antianginal effect and to look for a dose-response relationship and for attenuation of effect if any on continued administration. The mean +/- SEM exercise time on placebo was 6.7 +/- 0.6 min, increasing to 8.6 +/- 8 min (p less than 0.02) with 2.6 mg tds dosage and 8.4 +/- 0.7 min (p less than 0.01) with 6.5 mg tds of oral nitroglycerin. None of the other exercise-derived indices were altered significantly by oral nitroglycerin. Two patients were withdrawn because of severe headaches and both were receiving the higher dose. The data did not demonstrate any dose-response relationship but confirmed the anti-anginal efficacy of sustained action oral nitroglycerin. This efficacy did not show any significant attenuation of effect on continued administration, indicating a possible lack of development of tolerance.

Recent developments in the use of nitrates for treatment of angina pectoris

Organic nitrates are effective in the treatment and prophylaxis of angina pectoris. The major clinical problem of tolerance may be avoided if the daily plasma concentrations of the active metabolite, isosorbide-5-mononitrate are maintained at 100-300 ng/ml. The most promising development in achieving this is the use of sustained release preparations.

Nitrates

Nitroglycerin and the long-acting nitrates are playing an increasingly important role in cardiovascular medicine. These agents are recommended in all of the various anginal syndromes and are as effective as the beta-blockers and calcium channel antagonists. There is a definite place for nitrate therapy in treating the complications of acute myocardial infarction. These drugs are also highly effective as unloading therapy in congestive heart failure. The mechanisms of action of the nitrates are reviewed in this article. Information is provided regarding nitrate efficacy in all the major clinical syndromes in which these drugs are used. Finally, appropriate dosing strategies are suggested that should eliminate the potential problem of nitrate tolerance.

Nitrate tolerance

The organic nitrates are the most widely used agents in the management of patients with angina pectoris. When initially administered by the oral route, the nitrates produce profound changes in systemic hemodynamics and significant and prolonged improvement in exercise duration. It has been shown that during short periods of regular oral nitrate administration, the hemodynamic, antiischemic and antianginal effects of the nitrates are greatly reduced. Thus, when initially administered, oral isosorbide dinitrate prolongs exercise duration for a period of several hours, but during sustained 4-times-daily therapy, exercise tolerance is improved for only 2 hours after administration. Studies with transdermal preparations of isosorbide dinitrate and nitroglycerin also show improvement during short-term administration for up to 8 hours, but after several days of once-daily therapy, the effects of these agents are similar to placebo. It is apparent that nitrate tolerance is a clinically relevant problem. Although tolerance develops rapidly during nitrate therapy, it is reversed promptly during nitrate-free periods. Oral nitrates maintain their antianginal effects when given 2 or 3 times daily with provision of a nitrate-free period. Studies are currently underway to investigate the effects of intermittent administration schedules with transdermal nitrate preparations.

Induction and circumvention of nitrate tolerance applying different dosage intervals

There is increasing evidence that constant nitrate plasma levels, as induced by at least three-times-daily ingestions of isosorbide dinitrate in sustained-release form, lead to an attenuation or even complete loss of the anti-ischemic effects (nitrate tolerance). Therefore, the dependence of tolerance development on dosage intervals according to once-daily and twice-daily ingestions was assessed. Tablets of isosorbide dinitrate (80 mg) in sustained-release form were administered once-daily at 8 A.M. (dosage interval 24 hours) or twice-daily at 8 A.M. and 8 P.M. (dosage interval 12 hours), as well as at 8 A.M. and 2 P.M., respectively (maximal dosage interval 18 hours). A total of 34 patients with angiographically proven coronary artery disease, a history of stable, exercise-dependent angina pectoris, and a reproducible, exercise-induced ST-segment depression of at least 0.15 mV (1.5 mm), who initially showed a response to 80 mg of isosorbide dinitrate, were enrolled. The anti-ischemic effects of isosorbide dinitrate on exercise-induced ischemia were objectively determined by the measurement of exercise-induced ST-segment depression before as well as two, six, and 12 hours after the ingestion at the first and the 15th day of the studies. Since the dosage interval of 12 hours resulted in constant plasma levels, the initially beneficial anti-ischemic effects of isosorbide dinitrate were considerably attenuated after two weeks of treatment. In contrast, the once-daily regimen with its intermittent peaks and valleys of nitrate plasma levels showed identical anti-ischemic effects at the 15th day as compared with the first day. Ingestions at 8 A.M. and 2 P.M. also circumvented the development of nitrate tolerance, however, combined with an even more pronounced anti-ischemic effect after 12 hours as compared with the once-daily regimen. Thus, the circumvention of nitrate tolerance requires a daily "nitrate-poor" interval. The best compromise between a maximal possible anti-ischemic effect and the circumvention of tolerance development was found for the "eccentric" dosage regimen in which the tablets were ingested in the morning and early afternoon.

Comparison of nitroglycerin-TTS and long-acting nitroglycerin tablets in the treatment of angina pectoris: a double-blind controlled study

A cohort of 99 patients with severe, stable angina pectoris participated in a 26-week double-blind, between-patient trial of a transdermal therapeutic system (TTS) Nitroglycerin-TTS 5 mg/24 h and long-acting nitroglycerin tablets, 10.4 mg daily. The variables registered included daily sublingual nitroglycerin requirement, daily anginal attack rate, exercise test performance with ECG recordings, and a subjective patient evaluation on a visual analogue scale. There were no significant differences in the efficacy of the treatment between the two groups. Nor could we find any difference in the efficacy between the initial single-blind placebo treatment and the active nitroglycerin treatments.

New therapeutic modalities for the treatment of elderly patients with ischemic heart disease

In developing a treatment plan for elderly patients with ischemic heart disease, it is important to appreciate that the pathophysiologic process and aging influence the type of response produced by various drugs. The aging process also alters the way drugs are absorbed, distributed, and eliminated. Each of these variables must be considered in deciding which drugs should be used and how they should be administered.

The haemodynamic and anti-ischaemic effects of a single tablet of 80 mg isosorbide dinitrate in slow-release formulation and a review of nitrate tolerance

There is increasing evidence that relatively constant plasma nitrate concentrations induced by 3-times-daily administration of isosorbide dinitrate can lead to an attenuation or even complete loss of the drug's anti-ischaemic effects (nitrate tolerance). We therefore assessed the dependence of nitrate tolerance development from the haemodynamic and anti-ischaemic effects of a slow-release tablet formulation of isosorbide dinitrate 80 mg, administered according to different daily dosage regimens in patients with angina. It was found that a once-daily regimen, with its consequent peak and trough plasma nitrate concentrations, is capable of protecting against exercise-induced myocardial ischaemia for about 12 hours with the circumvention of nitrate tolerance.

Nitrate tolerance

Nitrates are widely used in anginal prophylaxis. In spite of the fact that the concept of nitrate tolerance was first put forward many years ago, the question of tolerance has remained controversial. There is widespread agreement that tolerance does occur to the effects of nitrates on arterial pressure. In contrast, tolerance to the venous and pulmonary effects is disputed. Similarly, the possibility of tolerance to the antianginal effects remains at issue. In this review, I discuss the factors which may have contributed to conflicting results in different studies, in particular recent findings on the rapidity of onset and reversal of tolerance. Tolerance develops rapidly on initiation of treatment and disappears equally rapidly on its discontinuation. In addition, tolerance appears to be a function of plasma nitrate profile. It is most likely to occur when plasma nitrate levels are constant and least likely when nitrate levels fluctuate. Furthermore, the provision of a daily nitrate free interval may protect against the development of tolerance. I then discuss the implications of these findings for patient management. They suggest that nitrate prophylaxis should not be used continuously, if this can be avoided. Rather, prophylaxis should be tailored to the individual to provide protection at times of maximum susceptibility, while allowing nitrate levels to fall at other times. The adequacy of antianginal protection with drug regimens incorporating a nitrate free interval requires further assessment. Similarly, the possibility that a nitrate free interval might lead to withdrawal effects and exacerbation of angina needs to be excluded.

Does placebo improve indexes of effort-induced myocardial ischemia? An objective study in 150 patients with chronic stable angina pectoris

The effects of placebo were studied in 150 patients (135 men, 15 women) aged 42 to 75 years with stable exertional angina pectoris, using multistage graded exercise testing. Treadmill exercise, using on-line computer analysis of the electrocardiogram, was performed after a basal period, during which time the patients had no treatment for 2 weeks, and after 2 weeks of placebo therapy. Mean exercise time during no treatment was 6.0 +/- 0.2 minutes and during placebo was 6.1 +/- 0.2 minutes (difference not significant). Similarly, time to development of 1 mm of ST-segment depression of 4.0 +/- 0.2 minutes without treatment was 4.1 +/- 0.2 minutes after 2 weeks of placebo therapy (difference not significant). Placebo failed to show any effect on rest or maximal heart rate or on maximal ST-segment depression. It also failed to increase exercise tolerance or to improve other objective indexes of effort-induced myocardial ischemia in both single-and double-blind protocols in patients with stable exertional angina pectoris. Therefore, placebo control of antianginal drug trials that use exercise testing for evaluation of effect is unnecessary and can be omitted.

The bioavailability of oral nitroglycerin

In the 1970's, the efficacy of oral nitroglycerin therapy was seriously challenged, primarily on the basis of animal studies showing complete first-pass hepatic metabolism of nitroglycerin. Today, it is generally accepted that high oral doses of nitroglycerin do show antianginal efficacy. It has been suggested that this efficacy results from saturation of hepatic metabolism by the large oral doses administered, although the experimental evidence in humans purporting to support this may be questioned. In the present investigation, the bioavailability of oral nitroglycerin when administered in a capsule dosage form and as a solution was determined. Oral doses of nitroglycerin were less than 1% bioavailable. However, substantially high concentrations of the relatively low activity dinitrate metabolites were measured in plasma. We hypothesize that the activity of oral nitroglycerin preparations may result from high concentrations of the dinitrate metabolites, although this was not directly tested in the bioavailability studies described here.

Nitroglycerin lingual spray: clinical efficacy and dose-response relation

Twenty patients with chronic, stable, exercise-induced angina pectoris were studied after receiving lingual sprays that delivered 0.2, 0.4 and 0.8 mg of nitroglycerin (GTN). The hemodynamic effects and changes in exercise time to the onset of angina and to the development of moderate angina were compared with those of placebo spray and 0.4 mg of sublingual GTN. A dose-response relation was apparent with the 3 doses of active spray for heart rate at rest but not for standing systolic blood pressure. Sublingual GTN produced effects similar to those with 0.4 and 0.8 mg of GTN spray, but exceeded the response to 0.2 mg of GTN spray. Treadmill walking time to the onset of angina and to the development of moderate angina was prolonged with each dose of GTN spray and showed a dose-response relation with significantly greater effects with increasing doses of GTN spray. This study indicates that GTN lingual spray is effective in the prophylaxis of angina and should be effective in the therapy of exercise-induced or spontaneous episodes of angina pectoris. The dose of 0.4 or 0.8 mg would appear to be most effective and similar to 0.4 mg of sublingual GTN.

Holter recording during treadmill testing in assessing myocardial ischemic changes

One hundred forty-four patients underwent a Bruce protocol treadmill exercise test during which an electrocardiogram (ECG) was recorded simultaneously with a 2-channel Holter recorder with bipolar V3- and V5-like leads and by a conventional 12-lead system. Sixty-eight patients had no ST depression on either the Holter or on the 12-lead ECG during the exercise test, whereas in 70 patients ischemic changes were recorded by both methods; thus, in 138 of the 144 patients (96%), the results of the 2 tests were concordant. The severity of ST depression, as judged by the heart rate at which ischemic changes were first noted and the maximal ST depression observed, were similar on both recording systems. The Holter system identified 6 of the 7 patients whose ischemic changes were confined to the inferior wall on the 12-lead ECG. The addition of the V3 lead as a second ischemic lead increased the ischemia detection by 10%. Ninety-five patients also underwent coronary arteriography. In these patients the sensitivity of the Holter system during exercise in detecting significant coronary artery disease was 81% and that of 12-lead ECG was 84%, the specificity was 85% and 85%, respectively, and the positive predictive value 91% and 91%, respectively. Thus, the 2-channel Holter recording system with bipolar V3- and V5-like leads was as accurate as the 12-lead system in detecting ischemic changes during exercise and proved that ambulatory monitoring system can reliably reproduce ST segment.

Pharmacokinetics of nitroglycerin after parenteral and oral dosing in the rat

The pharmacokinetics of nitroglycerin was characterized in detail using venous plasma after different intravenous bolus doses (0.15-2.48 mg/kg), intra-arterial infusion (8.2 micrograms/min over 5 h), and oral doses (7-100 mg/kg). Venous plasma clearance was found to be approximately 650 mL/kg and was independent of the intravenous or intra-arterial dose. This confirmed earlier reports that the venous plasma clearance of nitroglycerin in rats exceeded the value of normal cardiac output. A terminal half-life of approximately 15 min was observed after high intravenous bolus doses of nitroglycerin. This slow disappearance phase was likely rate limited by redistribution of drug back into the plasma. The bioavailability of oral nitroglycerin (F) showed an apparent Michaelis-Menten dependency on dose. F was less than 5% at doses less than 20 mg/kg, but increased to a plateau of approximately 20% from 50-100 mg/kg. First-pass metabolism of nitroglycerin is thus apparently controlled by at least two systems (sites or enzymes). Coadministration of mannitol hexanitrate, a potential competitive inhibitor of first-pass metabolism, did not increase F.

Nitrate delivery systems in perspective. A decade of progress

In recent years the use of nitroglycerin and long-acting nitrate compounds in clinical practice has been increasing. Only 10 to 15 years ago these drugs, at least in oral formulation, were felt to have no clinical utility because of concern that potent hepatic enzyme activity would degrade sufficient amounts of the nitrate compounds from reaching the systemic circulation. However, it is now recognized that oral nitrate administration when given in sufficient amounts achieves therapeutic plasma concentrations and desired clinical effects. Nitrates are routinely used for the treatment of stable and unstable angina and also play a role in therapy for complications of myocardial infarction. Nitrates are very effective agents for preload reduction in vasodilator therapy of congestive heart failure. A wide variety of nitrate delivery systems, including the standard oral and sublingual formulations, and as well as the new transdermal nitroglycerin discs and buccal nitroglycerin, are now available. Sublingual nitroglycerin, isosorbide dinitrate, and buccal nitroglycerin are used for acute treatment of attacks of ischemic chest pain. For ambulatory patients, long-acting therapy can be administered by oral, topical ointment, transdermal disc, and buccal nitroglycerin formulations. Each compound has a slightly different onset and duration of action, which is in part dose-dependent. The relative merits and problems with each of the formulations are reviewed. Intravenous nitroglycerin is now commercially available and plays an increasing role in the intensive care units. It is an ideal drug for acute chest pain syndromes, including acute myocardial infarction. Specialized tubing does not need to be employed. The wide variety of nitrate delivery systems available to physicians makes use of this tried and true therapy practical and easy to carry out for clinicians.

Oral sustained-release nitroglycerin in chronic stable angina: a multicenter, double-blind, randomized crossover trial

Forty-six patients with stable angina pectoris were randomized to receive either oral sustained-release nitroglycerin (SRNG, 6.5 mg) or placebo (P) 3 times a day for a 2-week double-blind trial. They were investigated for the frequency of anginal episodes, for sublingual nitroglycerin consumption and for exercise tolerance. There was a slight but significant decrease in the number of anginal episodes (6.4 +/- 1.5 episodes/week with P, 4.9 +/- 1.7 with SRNG, p less than 0.005) and sublingual nitroglycerin consumption (3.9 +/- 1 tablets/week with P, 2.7 +/- 1 with SRNG, p less than 0.005). The patients performed 3 upright multistage (increments of 30 W every 3 minutes) exercise tests on a bicycle ergometer before the start of the study and 1 hour after the intake of SRNG or P, at the end of each double-blind phase. Exercise capacity, expressed as exercise duration, increased from 8.9 +/- 3.8 minutes with P to 10.2 +/- 3.8 minutes with SRNG (14.6%; p less than 0.001). At symptom-limited exercise, ST depression was significantly reduced (p less than 0.05) during the SRNG phase. Thirty-four patients (74%) reached a higher peak heart rate (139 beats/min with P, 145 beats/min with SRNG; p less than 0.001) and 35 patients (76%) a higher rate-pressure product (+6%; p less than 0.001). These changes in exercise tolerance are relatively modest and at least 11 patients would have benefited from larger doses of nitrates.(ABSTRACT TRUNCATED AT 250 WORDS)

Ambulatory electrocardiographic ST segment changes in healthy volunteers

Twenty four hour ambulatory monitoring was performed on 120 healthy volunteers using a frequency modulated recorder: 50 men and 50 women below 40 years and 20 men between 40 and 60 years were studied. Twenty eight subjects had episodes of ST segment elevation (range 1-3 mm), which occurred almost invariably at night with a slow heart rate 62.4 +/- 10.4 beats/min). ST segment elevation occurred most often in men, and was not found in subjects over the age of 37. Also in 10 subjects horizontal or downsloping ST segment depression (range 1-2 mm) was recorded, usually in association with tachycardia (135 +/- 10.5 beats/min). Nine of these exercised on a bicycle ergometer, and widespread ST segment depression was observed in eight. Thus ST segment changes, which are often interpreted as myocardial ischaemia in patients with ischaemic heart disease, are commonly seen in 24 hour electrocardiographic monitoring of healthy volunteers.

Effect of oral sustained-release nitroglycerin on exercise capacity in angina pectoris: dose-response relation and duration of action during double-blind crossover randomized acute therapy

Ten men with documented coronary artery disease and stable exertional angina underwent a double-blind crossover study to examine the benefit and the duration of action on their symptom-limited exercise capacity of 2 doses (2.5 and 6.5 mg) of sustained-release nitroglycerin (SRNG). A multistage bicycle test was performed in the sitting position by steps of 30 W each 3 minutes until the onset of typical angina pectoris. It was performed 24 hours before the start of the study; 1 and 5 hours after administration of placebo, and repeated after 2.5 and 6.5 mg of SRNG administered in a double-blind crossover study according to a 4 successive days protocol. No differences appeared between administration of placebo (1 and 5 hours) and the results obtained at the first exercise test. The dose of 2.5 mg of SRNG was effective on the symptom-limited working capacity but only at 1 hour (+9%; p less than 0.01). The dose of 6.5 mg was more effective both at 1 hour (+25%; p less than 0.001) and at 5 hours (+27%; p less than 0.001). All patients had angina at a higher heart rate (+5 to 8%; p = NS [not significant] and p less than 0.01), whereas systolic blood pressure and double product tended to be slightly but insignificantly increased. S-T depression at the onset of angina was insignificantly changed with placebo, and 2.5 and 6.5 mg of SRNG. It is concluded that 6.5 mg of orally administered SRNG is effective during at least 5 hours, and that the magnitude of the benefit and its duration are dose-related.

Efficacy of sustained-release buccal nitroglycerin in patients with angina pectoris. New and long-acting therapy demonstrated by exercise

The antianginal efficacy of a single sustained-release buccal nitroglycerin (BNTG) tablet was assessed in 16 patients with known coronary artery disease. Patients were trained in bicycle ergometry to induce angina pectoris within three to five minutes. A hemodynamically effective dose of BNTG was identified. Patients were tested at baseline and given placebo and BNTG in a randomized, double-blind manner on consecutive days. They were tested at 0.5, 1, 3, and 5 hours after drug administration. The average increase in exercise duration with BNTG compared with placebo at 0.5 hours was 40 percent (p less than 0.01); at 1 hour was 31 percent (p less than 0.01); at 3 hours was 27 percent (p less than 0.01); at 5 hours was 15 percent (p = NS). In a subset of ten patients in whom the tablet was maintained in the buccal pouch for five or more hours before dissolving, increase in exercise duration was significant at all times tested (p less than 0.05). We conclude that BNTG is an effective modality of administering nitroglycerin for rapid and prolonged effect with reduction in angina pectoris and increase in exercise duration which may persist for at least five hours.

Elimination of glyceryl trinitrate: effects of sex, age, species and route of administration

1 Orally administered glyceryl trinitrate to rats undergoes extensive first pass metabolism leading to low bioavailability. 2 Sex differences in the plasma elimination of glyceryl trinitrate were seen in the rat, the female exhibiting the longer plasma half-life. No sex differences in this respect were detected in the rabbit. 3 The plasma half-life of glyceryl trinitrate was longer and the volume of distribution larger, in older animals. 4 The plasma elimination of glyceryl trinitrate was different in various animal species. There was a good correlation between plasma half-life and animal bodyweight.

Rectal absorption of nitroglycerin in the rat: avoidance of first-pass metabolism as a function of rectal length exposure

Nitroglycerin administered orally undergoes substantial presystemic elimination. It was shown recently that first-pass hepatic metabolism of high clearance drugs can be substantially avoided via rectal administration. In applying this concept to nitroglycerin in rats, it was found that unrestricted rectal instillation of nitroglycerin (at 3.5-mg/kg dose) gave a mean +/-SD bioavailability of 26.7 +/- 7.0% (n=6) compared to 1.8 +/- 0.9% (n=5) from oral dosing. This mode of dosing did not lead to complete avoidance of first-pass metabolism of nitroglycerin in rats. When the rectal exposure length to nitroglycerin was restricted to 3.5 cm from the anus, the mean +/-SD bioavailability increased to 83.5 +/- 74.5% (n=14). However, the variability in bioavailability was extremely large. When the rectal exposure length was restricted to 2.0 cm from the anus (at 1.75-mg/kg dose), nitroglycerin bioavailability was estimated at 91.2 +/- 30.4% (n=6). The plasma nitroglycerin concentrations (greater than 5 min) obtained after this mode of administration were similar to those achieved after intravenous dosing. The data showed that substantial avoidance of presystemic nitroglycerin metabolism can be achieved via rectal administration. This avoidance can be nearly complete if nitroglycerin is limited in exposure to only the lower rat rectum. It was also demonstrated that sustained (at least 24 hr) nitroglycerin delivery via the rat rectal route was feasible with an experimental osmotic minipump. This delivery system also produced nearly complete bioavailability for nitroglycerin in the rat.