Usefulness of long-acting nitrates in cardiovascular disease

Treatment of Perioperative Myocardial Ischemia

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

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 Two patients were withdrawn because of severe headaches and both were receiving the higher dose.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.

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.

Current perspectives in treatment of angina pectoris

The most appropriate treatment for a patient with angina pectoris depends on the underlying pathophysiologic process and whether any associated illness is present. Each patient's clinical history must be carefully reviewed so the hemodynamic process responsible for the clinical picture is understood. If symptoms are produced mostly by an increase in myocardial oxygen demand, efforts should be directed toward reducing the demand or improving coronary blood flow to meet the demand. If symptoms appear to occur secondary to vasospasm, treatment should be directed toward relief of spasm with potent vasodilating agents, such as calcium channel blockers. Most patients have a clinical picture consistent with mixed angina and may require combination therapy. Treatment of associated illnesses and the safety of pharmacologic agents used in their presence should be carefully considered. Finally, if treatment is to successfully reduce the incidence of serious cardiac events and prolong life, the goal of therapy should be relief of the total ischemic burden on the heart.

Pharmacology of nitroglycerin and long-acting nitrates

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

Rational medical therapy for stable angina pectoris

Important advances in understanding of the pathophysiology and medical treatment of angina pectoris have taken place in the past few years. Angina may occur from increased oxygen demands that cannot be met by a diseased coronary circulation and/or primary decrease in oxygen supply to the heart. Three major categories of pharmacologic agents are used in treating angina. Nitrates remain the first-line approach; they are inexpensive and available in many delivery forms. Beta blockers are also effective in the treatment of angina pectoris, and despite their side effects, are particularly useful in effort angina. The newest agents, the calcium channel blockers, are efficacious in all types of anginal syndromes. Each group of drugs acts differently on the various pathophysiologic mechanisms that contribute to the production of angina. This commentary critically reviews the major groups of anti-anginal drugs and places them in a clinical perspective. Guidelines for choosing an appropriate agent for the treatment of angina are proposed. Special situations, such as angina and hypertension, congestive heart failure, or post-myocardial infarction angina, are discussed with respect to selection of anti-anginal therapy. The proper utilization of nitrates, calcium channel blockers, and beta blockers, alone or in combination, provides a bright future for patients with ischemic heart disease.

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)

Nitroglycerin and long-acting nitrates in clinical practice

Nitrates are potent relaxers of vascular smooth muscle and act by dilating veins, arteries, and arterioles (especially at high doses). Their clinical effects have been considered to be dominantly related to peripheral actions: systemic venodilatation and a decrease in systemic vascular resistance, reducing the preload and afterload of the heart. Considerable experimental work confirms potent salutary effects on the coronary circulation. These drugs are readily absorbed across mucosal surfaces; they are available in multiple formulations, including sublingual, buccal, oral, and topical delivery systems. Nitrate administration should begin with low doses and increased to doses that are often higher than previously recommended until a specific clinical end point or limiting side effects occur. Organic nitrate esters are effective in the treatment of stable angina pectoris, unstable angina, coronary vasospastic syndromes, and in vasodilator therapy in severe congestive heart failure. The pathophysiology of these syndromes is reviewed with respect to the clinical actions of nitrates on the central and peripheral circulations. The side effects of nitrates include headache, dizziness, and nausea. Nitrate tolerance, a controversial subject, does not appear to be an important clinical problem. Using the guidelines presented in this review, nitrate therapy provides effective, inexpensive, well-tolerated therapy for many patients with cardiovascular disease.

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.

New nitrate delivery systems: buccal nitroglycerin

BN, a new nitrate formulation, has recently been made available. The main advantages of this medication is the combination of prompt onset of action, comparable to that of sublingual NTG, and sustained activity that persists for many hours. The tablet remains pharmacologically effective as long as it remains in the buccal pouch. A variety of studies indicate that BN is well tolerated by patients, acts promptly to provide protection against anginal pain, and has sustained efficacy that persists for 2 to 6 hours. Clinical investigations using serial treadmill testing in patients with angina demonstrate clinical effectiveness and bioactivity of BN beginning within minutes and lasting over 4 hours. The potential advantages of this preparation are discussed, and the formulation is compared to other available longacting nitrates. BN is an effective new addition to the nitrate armamentarium.

Pharmaceutical considerations of nitroglycerin

During the past few years, there have been rapid changes in the pharmaceutical uses of nitroglycerin. New dosage forms and new delivery systems have become available, which have resulted in potential confusion to all concerned with the proper use of these systems. The goal of this review is to prevent confusion and to bring all the relevant information together. The various analytical techniques available for quality control of the dosage forms and for the study of the pharmacokinetics are reviewed, with the intent of enabling the reader to identify pertinent references rapidly. The interaction of nitroglycerin with packaging and plastic delivery devices is also reviewed so that the reader can make informed choices. Finally, the clinical pharmacy and pharmacokinetics are reviewed so as to bring the reader up to date in that area. After reading this article, the areas of nitroglycerin research that still need to be explored should be apparent.

Cardiovascular effects of a newly synthesized cardiotonic agent (TA-064) on normal and diseased hearts

A new inotropic agent, TA-064, (-)-alpha-(3,4-dimethoxyphenethylaminomethyl)-4-hydroxybenzylalcohol, was shown to have strong effects in experimental animals. Its effectiveness and associated adverse effects were tested in humans invasively (n = 6) and noninvasively (n = 17). Increasing doses of intravenous infusion (1, 2, and 4 micrograms/kg/min) increased plasma levels to 15, 35, and 82 ng/ml, respectively, resulting in marked increases in the peak rate of left ventricular pressure rise (dP/dt) (1,450 +/- 63 to 3,042 +/- 349 mm Hg/s) (mean +/- standard error of the mean [SEM], p less than 0.01) and the ratio of dP/dt to left ventricular pressure at a developed pressure of 40 mm Hg (25 +/- 3 to 39 +/- 2 s-1) (p less than 0.01), with a reduction in left ventricular end-diastolic pressure (12 +/- 2 to 4 +/- 1 mm Hg) (p less than 0.01). Minimal or no changes were seen in heart rate and left ventricular systolic pressure. After a single oral dose (10 mg), the plasma level reached its peak at 90 minutes (16 +/- 9 ng/ml, n = 17). A positive inotropic effect was confirmed echocardiographically in both healthy volunteers (n = 8) and patients with congestive heart failure (CHF) (n = 9) who were maximally treated with conventional regimens: increase in mean velocity of circumferential fiber shortening (healthy volunteers: 1.29 +/- 0.05 to 1.60 +/- 0.11 circ/s [p less than 0.05]; patients with CHF: 0.69 +/- 0.08 to 0.93 +/- 0.09 circ/s [p less than 0.01]), ejection fraction (healthy volunteers: 68 +/- 2 to 75 +/- 2% [p less than 0.05], patients with CHF: 37 +/- 4 to 45 +/- 5% [p less than 0.01]) without change in heart rate. The cardiac index was increased only in the CHF group (2.71 +/- 0.22 to 3.21 +/- 0.24 liters/min/m2) (p less than 0.05). No significant untoward effects were observed. Thus TA-064 is a potent inotropic agent and can be used either parenterally or orally. Salutary effects can be expected in patients with congestive heart failure who are treated with digitalis and diuretic agents.

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.

Animal pharmacology of nitroglycerin

Nitroglycerin, first introduced over a hundred years ago, is now finding wider clinical applications. To a large degree, the renewed interest in the clinical pharmacologic usage of nitroglycerin is due to the availability of new formulations and drug delivery systems. The current review focuses on the physiological and pharmacological actions of nitroglycerin in mammals. Routes of nitroglycerin metabolism, biochemistry and absorption are discussed. The phenomenon of nitroglycerin tolerance is illustrated and related to specific quantitative alterations occurring at the cellular level. The cardiovascular effects of nitroglycerin are discussed in terms of its effects on coronary flow, the myocardium itself, and on the peripheral vasculature. The early speculation of Murrell (3) that nitroglycerin "would probably prove of service in the treatment of angina pectoris ... and other vascular disorders ..." has now been realized.

Statistics in question: assessing clinical trials--design II

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Blood levels after sublingual nitroglycerin

Pharmacokinetic analysis of nitroglycerin (GTN) has been hampered by the lack of a sensitive and specific method for measuring GTN in blood. Therefore, we examined the appearance of GTN in blood after administering 0.6 mg sublingually in 10 studies of normal volunteers. We used a gas-liquid chromatographic method with electron-capture detection and isosorbide dinitrate as the internal standard. GTN appeared in blood at 0.5 minutes, reached a peak of 2.3 +/- 0.36 ng/ml at 2 minutes, fell to 50% of peak value at 7.5 minutes and was barely detectable at 20 minutes. These blood levels paralleled the changes in heart rate and systolic blood pressure. These data show rapid appearance and disappearance of GTN from blood after sublingual administration, a large volume of distribution, and a rapid rate of total body clearance that precludes the liver from being the sole elimination site. This method for analysis of GTN and isosorbide dinitrate should be helpful in defining the role of chronic nitrate therapy.