Nitrates

Benefits of optimising drug treatment in home-dwelling elderly patients with coronary artery disease

Coronary artery disease (CAD) is prevalent in the elderly and often leads to disability. Consequently, strategies for optimising the prevention and treatment of CAD in the elderly are important from both the individual and societal perspectives. Although it is common knowledge that the elderly are heavy consumers of drugs, there is evidence to show that there is under-prescribing of evidence-based medical therapies in the home-dwelling elderly coronary patient and there may be overuse of some non-evidence-based (antioxidants) and purely symptomatic treatments. In particular, aspirin (acetylsalicylic acid), beta-adrenoceptor antagonists, ACE inhibitors and HMG-CoA reductase inhibitors are under-utilised. Although the evidence base is largely drawn from trials including patients younger than 75 years, it is reasonable to assume that the data applies to patients aged over 75 years and that better use of evidence-based medicines would provide benefits to the home-dwelling aged patient. Evidence from the few multifactorial studies available suggest possible benefits including reduction of cardiovascular events, less disability and better quality of life in old age. At the societal level, this would be reflected in fewer hospitalisations and institutionalisations, which means decreased cost of elderly care.

Controlled hypotension in children: a critical review of available agents

Due to the potential for the transmission of infectious diseases with the homologous transfusion of blood products, there has been an increased interest in measures to limit intraoperative blood loss and avoid the need for homologous transfusion during high-risk surgical procedures including spinal surgery. Controlled hypotension (also referred to as deliberate or induced hypotension), defined as a reduction of systolic blood pressure to 80 to 90 mm Hg, a reduction of mean arterial pressure (MAP) to 50 to 65 mm Hg or a 30% reduction of baseline MAP, is one technique that has been used to limit intraoperative blood loss. In the adult population, several agents have been used alone or in combination for controlled hypotension including the inhalational anesthetic agents, direct-acting vasodilators such as nitroglycerin (glyceryl trinitrate) and nitroprusside, beta-adrenoceptor antagonists, and calcium channel antagonists. Despite clinical studies that have clearly demonstrated a reduction in blood loss with controlled hypotension when compared with the normotensive state and despite potential theoretical issues with each agent, there are no definitive studies demonstrating the preferred pharmacologic agent. When considering the pediatric-aged patient, studies have reported the use of the inhalational agent sevoflurane, the alpha(2)-adrenoceptor agonist dexmedetomidine as well as various vasodilators including sodium nitroprusside, nitroglycerin, fenoldopam, and alprostadil for controlled hypotension. Sevoflurane offers the advantages of easy dosage titration, no need for an additional intravenous infusion as well as providing anesthesia in addition to controlled hypotension. Disadvantages include a slightly higher cost than some of the intravenous agents and the inability to monitor evoked potentials with high sevoflurane concentrations. Whereas sodium nitroprusside, nicardipine and fenoldopam all provide the desired level of hypotension in pediatric-aged patients, nitroglycerin was not effective in this age group of patients in one study. When comparing nicardipine and sodium nitroprusside, nicardipine offers the potential advantages of fewer episodes of excessive hypotension, less rebound tachycardia and, in one study, less blood loss. Although fenoldopam has been shown to be effective, cost issues may limit is widespread application for this technique. The pharmacologic profile of dexmedetomidine indicates that this drug has potential in controlled hypotension and clinical data are needed to define its role.

Effect of chronic nitrate treatment on retinal vessel caliber in open-angle glaucoma

PURPOSE

A recent report has suggested that nitrate therapy may delay the progression of glaucomatous damage. To investigate the mechanism that may mediate this effect, we sought to determine whether nitrate therapy is associated with retinal vasodilatation in patients with glaucoma.

METHODS

Retinal venous and arterial diameters were determined from color fundus photographs of the optic nerve head obtained during a retrospective study designed to investigate any potential effects of chronic nitrate treatment on the progression of glaucomatous pathology. Fourteen eyes of 14 patients who were receiving chronic nitrate therapy for systemic diseases unrelated to glaucoma were randomly selected. Vascular measurements were compared with those of 15 eyes of 15 control patients with glaucoma who did not receive any nitrate therapy.

RESULTS

In comparison with control patients, nitrate-treated patients showed significant average vasodilatation of 17% (P = .008) and 13% (P = .01) in the superior and inferior temporal retinal veins, respectively. A 5% increase in average retinal arterial diameter was also detected, but this was not statistically significant.

CONCLUSION

Chronic nitrate treatment is associated with retinal venous dilatation in patients with glaucoma. Although not assessed in this study, it is possible that a protective effect of nitrates may be mediated by a vasoactive effect leading to improved perfusion of the retina and perhaps the optic nerve head, in a similar fashion to what has been observed in the circulation of the heart. Additional studies of the effect of nitrates on the ocular circulation are needed, however, to support this speculation.

Pharmacologic drugs for controlled hypotension

Due to the risks of transfusion reactions and the transmission of infectious diseases, there has been increased interest in measures to limit intraoperative blood loss and avoid the need for homologous transfusion. Controlled hypotension is one technique that has been used to limit intraoperative blood loss. Several drugs have been used alone or in combination for controlled hypotension, including the inhalational anesthetics, direct acting vasodilators such as nitroglycerin and nitroprusside, beta adrenergic antagonists, and calcium channel blockers. Various drugs available to the clinician for controlled hypotension are reviewed.

Assessment and management of the client experiencing myocardial ischaemia

The management of myocardial ischemia requires prompt assessment and intervention. Nursing assessment should be systematic, with every possible clue being integrated to help form a diagnostic picture. Assessment includes not only pain assessment but also assessment of psychological status and physiological response. An understanding is required of normal coronary flow and myocardial perfusion in order to then intervene in a therapeutic manner. Management should be focused on pain relief, diminution of anxiety and strategies to redress myocardial oxygen demand/supply imbalance. This article discusses a systematic framework to facilitate prompt and effective assessment and management of a client experiencing myocardial ischaemia. It builds on the description of the neurological pathways of cardiac pain provided in Part 1, Beetson, R. Pain in the client experiencing myocardial ischaemia-Nursing assessment and management. Part 1-Neurophysiology and clinical manifestations of myocardial ischaemia pain.

Effects of an oral dose of isosorbide dinitrate on platelet function and fibrinolysis in healthy volunteers

1. A randomised double-blind placebo-controlled study was performed to investigate the effects of isosorbide dinitrate (ISDN; 20 mg orally) on various aspects of platelet function and fibrinolysis in vivo in 12 healthy volunteers. 2. Measurements were performed at rest (before and after tablet ingestion) and during platelet activation by adrenaline (0.4 nmol kg-1 min-1; 30 min infusion). 3. At rest, ISDN did not alter plasma concentrations of beta-thromboglobulin (beta TG). EC50 values for ADP induced aggregation in vitro (Born aggregometry) or ex vivo filtragometry readings. Adrenaline markedly increased platelet aggregability in vivo as measured by filtragometry and elevated levels of beta TG in plasma. ISDN treatment did not affect these responses in the group as a whole. 4. Individuals responding to ISDN with more pronounced vasodilatation at rest showed a lesser increase in aggregability during the ensuing adrenaline infusion (r = -0.66, P = 0.02) despite higher adrenaline levels during ISDN. In individuals showing a significant decrease in systolic blood pressure (n = 8) ISDN tended to attenuate the adrenaline induced increase in platelet aggregability (filtragometry; P = 0.08), despite higher plasma adrenaline and noradrenaline levels after ISDN ingestion. 5. Plasma concentrations of ISDN and its active metabolites isosorbide-5-mononitrate and isosorbide-2-mononitrate were not correlated to haemodynamic or platelet variables. 6. Fibrinolytic activity (t-PA antigen and activity, PAI-1 antigen and activity) increased similarly during the adrenaline infusion following ISDN and placebo. 7. It is concluded that ISDN may affect platelet aggregation responses to adrenaline in vivo, but only in individuals showing significant haemodynamic responses to ISDN.(ABSTRACT TRUNCATED AT 250 WORDS)

The prehospital use of nitroglycerin according to standing medical orders in an urban EMS system

PURPOSE

The purposes of this study are to quantify the use of nitroglycerin (NTG) in prehospital care, to detect deviations from the Standing Medical Orders (SMO), to determine the effectiveness of its administration, and the incidence of clinically significant adverse reactions (hypotension, bradycardia).

METHOD

Retrospective review of 7683 Advanced Life Support (ALS) telemetry, base-station contacts over a three month period (June, July, August 1990) to identify all prehospital patient contacts in which NTG was utilized.

SETTING

The Resource Hospital/Telemetry Base-Station and two community hospitals/Telemetry Base-Stations for the Chicago North EMS System.

RESULTS

There were 445 runs in which NTG was indicated as per SMO. Two hundred eighty-eight patients (64.7%) received NTG for appropriate indications as per SMO, 203 for ischemic chest pain (45.6%), 79 for pulmonary edema (17.7%), and six for both (1.3%). There were 157 (35.5%) runs in which NTG was indicated, but not administered. There were 22 patients who received NTG for indications that deviated from the SMO. Reassessment data concerning the subjective symptom was completed on 118 patients (40.9%), 92 (45.3%) patients with chest pain and 26 with dyspnea (32.9%). Following the administration of NTG, 21 patients (10.1%) with chest pain were unchanged, while 13 with dyspnea (15.3%) improved, 13 patients (15.3%) were unchanged, and none worsened. In 121 patients, the systolic blood pressure (SBP) decreased, while 24 were unchanged (5.4%), and 28 had an increase (6.3%). The mean initial value SBP was 176 +/- 44 mmHg and the repeat mean SBP was 164 +/- 41 mmHg with a mean decrease of 12 +/- 22 mmHg. The diastolic blood pressure (DBP) decreased in 87 patients, was unchanged in 53 (11.9%), and increased in 33 (7.4%). The initial mean DBP was 97 +/- 24 mmHg, the repeat mean DBP was 92 +/- 23 mmHg, a mean decrease of 5 +/- 15 mmHg. Only one patient became hypotensive with the administration of NTG and was successfully resuscitated with a fluid bolus of 300 ml normal saline.

CONCLUSIONS

In this EMS system, NTG is under-utilized based on the indications delineated by this system's SMOs. Reassessment is documented infrequently, but when completed, clinically significant adverse reactions are rare. Since the incidence of hypotension and bradycardia are rare, the inability to establish an IV line should not preclude the administration of NTG.

Tolerance, rebound, and time-zero effect of nitrate therapy

Both nitroglycerin and long-acting nitrates have proved effective in treating acute anginal pain. In recent years, however, development of tolerance with the continuous use of these agents has been documented. A pilot study demonstrated attenuation of the therapeutic effect of high-dose, continuous transdermal nitroglycerin therapy, despite adequate plasma nitroglycerin levels. In a subsequent, larger Transdermal Nitroglycerin Cooperative Study, evidence of tolerance was detected within 24 hours of initiation of continuous nitroglycerin patch therapy at several different dose levels. Sustained pharmacologic activity has been achieved with the intermittent use of transdermal nitroglycerin, usually for 12 hours followed by a 12-hour drug-free period. When the patch is discontinued, however, some patients experience exacerbation, or rebound, of anginal symptoms and a worsening of exercise tolerance at the end of the drug-free period. Additional clinical research is therefore needed to determine the optimal intermittent dosing strategy.

A possible role for nitric oxide in glutamate (MSG)-induced Chinese restaurant syndrome, glutamate-induced asthma, 'hot-dog headache', pugilistic Alzheimer's disease, and other disorders

Endogenous glutamate is thought to be a major neurotransmitter. After binding to a cell membrane receptor there can be a stimulation of what can be called the nitric oxide (NO)-mediated neurotransmission pathway (NO-MNP). The activity of the enzyme that produces NO from arginine, NO synthase, and the level of NO become elevated. NO has little activity within the cell in which it is produced, but it rapidly leaks out of that cell and produces effects in neighboring cells. The NO-MNP can be activated to release NO in endothelial cells which in turn acts on neighboring vascular smooth muscle cells to induce vasodilation. Therefore, we suggest that exogenous, ingested glutamate, like endogenous glutamate, can lead to the same stimulation of the NO-MNP in sensitive individuals which would then cause the symptoms of the Chinese restaurant syndrome and/or glutamate-induced asthma. Further, since ingested nitrite and related compounds can be metabolized to NO, NO may more directly cause the symptoms of 'hot dog headache'. In addition, it has been suggested that NO production can also be controlled in endothelial cells by fluid forces that stimulate pressure receptors. Therefore, elevations of NO and stimulation of the NO-MNP may occur due to sudden, local, alterations of blood pressure during pugilistic activities and play a role in the symptoms of pugilistic Alzheimer's disease. If these ideas are correct, then inhibitors of the NO-MNP and/or temporary reduction of the plasma level of arginine may be useful in preventing at least some of the symptoms of these disorders.

Concurrent nitroglycerin administration decreases thrombolytic potential of tissue-type plasminogen activator

Dynamic coronary vasoconstriction may play a role in coronary artery reocclusion after successful thrombolysis. The effect of nitroglycerin on the thrombolytic effects of recombinant tissue-type plasminogen activator (rt-PA) was examined in dogs with an electrically induced occlusive coronary artery thrombus. Eleven dogs were randomly given rt-PA alone and seven rt-PA with nitroglycerin. The dose of rt-PA was 0.75 mg/kg body weight given over 20 min and the dose of nitroglycerin was 125 micrograms/min for 40 min. The reperfusion rate in the dogs given rt-PA alone was 73% (8 of 11 dogs) and that in the rt-PA plus nitroglycerin group was 57% (four of seven dogs) (p = NS). The time to thrombolysis (or reperfusion) in dogs receiving rt-PA plus nitroglycerin was 70% greater than in those receiving rt-PA alone (means +/- SD/29.8 +/- 9.9 versus 17.6 +/- 5.9 min, p less than 0.02), and the duration of reperfusion much shorter (11 +/- 17 versus 42 +/- 16 min, p less than 0.02). Peak coronary blood flow after reperfusion in dogs receiving rt-PA plus nitroglycerin was also less than in those receiving rt-PA alone (36 +/- 52 versus 63 +/- 20 ml/min, p less than 0.02). Reocclusion occurred in all dogs given rt-PA with nitroglycerin and in six of eight given rt-PA alone (p = NS). Plasma concentrations of rt-PA were lower when nitroglycerin was given with rt-PA alone (427 +/- 279 versus 1,471 +/- 600 ng/ml, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Sustained beneficial effect of a seventy-two hour intravenous infusion of nitroglycerin in patients with severe chronic congestive heart failure

To determine whether a 72-hour infusion of nitroglycerin produces hemodynamic improvement in patients with severe congestive heart failure and to assess the contributing role of various possible causes of hemodynamic tolerance to nitroglycerin, 19 patients received an infusion of nitroglycerin 1.5 micrograms/kg/min for 72 hours. In a subgroup of patients (n = 10), there was an increase in stroke work index and a decrease in ventricular filling pressures throughout the infusion and even after it was discontinued. Tolerance to the hemodynamic effects of nitroglycerin was partially reversed 8 hours after the infusion was stopped. Neurohumoral changes occurred but appeared to play only a minor role in the development of nitroglycerin tolerance. However, hematocrit fell 9 +/- 5%, which suggests that an increased intravascular volume contributed to tolerance. In summary: (1) a 72-hour infusion of nitroglycerin improves ventricular function in some patients with severe heart failure; (2) volume shifts from the extravascular to the intravascular compartments may, at least in part, be responsible for nitroglycerin tolerance; and (3) reflex neurohumoral activation may also play a small role in nitrate tolerance.

Buccal nitroglycerin decreases ischemic pain during coronary angioplasty: a double-blind, randomized, placebo-controlled study

Nitroglycerin (NTG) has the potential to reduce myocardial ischemia during percutaneous transluminal coronary angioplasty (PTCA). Buccal administration of NTG offers practical advantages compared to intravenous or intracoronary administration. In a double-blind, randomized, placebo-controlled study, 100 patients were given 5 mg of buccal NTG or placebo during PTCA. A scoring system for ischemic pain during balloon inflation was defined as pain intensity (0 to 5) multiplied by duration of pain after balloon deflation (1 = 0 to 30 seconds, 2 = 30 to 60 seconds, 3 = 60 to 120 seconds, 4 = greater than 120 seconds but subsiding, and 5 = until next inflation). Fourteen patients were excluded: 12 for vagal reaction (eight NTG and four placebo; p greater than 0.05) requiring atropine, making buccal absorption unreliable, and two for inability to dilate. Eighteen patients (nine NTG and nine placebo) had no pain during balloon inflation. Sixty-eight patients (32 NTG and 36 placebo) had ischemic pain with a pain score (mean +/- SD) of 4.8 +/- 3.8 for the NTG group versus 7.1 +/- 4.8 for the placebo group (p = 0.03). We conclude that buccal NTG significantly decreases myocardial ischemia during PTCA.

Sustained high-dose nitroglycerin transcutaneous patch therapy in angina pectoris: evidence for attenuation of effect over time

The safety and efficacy of using continuous high-dose transcutaneous nitroglycerin in doses up to 100 mg/24 hours in chronic stable angina was assessed in 20 patients using serial treadmill testing. Patients had first to show a response to sublingual nitroglycerin with a 20% improvement in exercise time. All patients were then titrated with 20 mg (40 cm2), 60 mg (120 cm2), 80 mg (160 cm2) or 100 mg (200 cm2) patches, until intolerable headache in association with a 10 mmHg reduction in blood pressure and a ten-beat increment in heart rate. Drug was then discontinued for 2 days and patients underwent three repeat stress tests to reestablish a consistent drug-free baseline. Patients were then randomized in double-blind fashion to receive either active patch (N = 11) in previous titration dose or placebo patch (N = 9), with treadmill tests performed at 0 (1 hour after previous patch removal), 4, and 24 hours after patch application at baseline and at weeks 1 and 2. Venous blood was obtained for measurement of plasma nitroglycerin levels. After the first 24 hours of active patch therapy, there was a significant reduction in systolic blood pressure (P = .05), a significant increase in heart rate (P = .01), and a minor increase in exercise tolerance (P = .06) compared to placebo. At weeks 1 and 2, there was an attenuation of drug effect in all of these parameters. Plasma nitroglycerin levels demonstrated consistently high plasma levels over each 24-hour dosing interval, on day 1, week 1, and week 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Profile of an ideal antianginal agent

Many antianginal agents are available for the treatment of coronary artery disease. These agents act by influencing the determinants of myocardial oxygen supply and demand. The 3 main classes of agents are the nitrates, beta-adrenergic blocking agents and the calcium entry blockers. Agents from all 3 classes have shown efficacy in treating both symptomatic and asymptomatic myocardial ischaemia. However, some patients cannot be treated with these agents because of side effects or contraindications. An ideal antianginal drug should effectively treat both angina and silent ischaemia. Additionally, it should be free of side effects, allow for maintenance of physical performance and be metabolically neutral. New agents are being developed which strive for this goal.