Effects of intermittent transdermal nitroglycerin on occurrence of ischemia after patch removal: results of the second transdermal intermittent dosing evaluation study (TIDES-II)

Nitrates for the prevention of cardiac morbidity and mortality in patients undergoing non-cardiac surgery

BACKGROUND

Cardiac complications are not uncommon in patients undergoing non-cardiac surgery, especially in patients with coronary artery disease (CAD) or at high risk of CAD. Perioperative cardiac complications can lead to mortality and morbidity, as well as higher costs for patient care. Nitrates, which are among the most commonly used cardiovascular drugs, perform the function of decreasing cardiac preload while improving cardiac blood perfusion. Sometimes, nitrates are administered to patients undergoing non-cardiac surgery to reduce the incidence of cardiac complications, especially for patients with CAD. However, their effects on patients' relevant outcomes remain controversial.

OBJECTIVES

• To assess effects of nitrates as compared with other interventions or placebo in reducing cardiac risk (such as death caused by cardiac factors, angina pectoris, acute myocardial infarction, acute heart failure and cardiac arrhythmia) in patients undergoing non-cardiac surgery.• To identify the influence of different routes and dosages of nitrates on patient outcomes.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE and the Chinese BioMedical Database until June 2014. We also searched relevant conference abstracts of important anaesthesiology or cardiology scientific meetings, the database of ongoing trials and Google Scholar.We reran the search in January 2016. We added three potential new studies of interest to the list of 'Studies awaiting classification' and will incorporate them into our formal review findings for the review update.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) comparing nitrates versus no treatment, placebo or other pharmacological interventions in participants (15 years of age and older) undergoing non-cardiac surgery under any type of anaesthesia.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures as expected by Cochrane. Two review authors selected trials, extracted data from included studies and assessed risk of bias. We resolved differences by discussion and, when necessary, sought help and suggestions from a third review author. We used a random-effects model for data analysis.

MAIN RESULTS

We included 27 randomized controlled trials (RCTs) (8244 participants analysed). Investigators reported 12 different comparisons of three different nitrates (nitroglycerin, isosorbide dinitrate and nicorandil) versus no treatment, placebo or other pharmacological interventions. All participants were older than 15 years of age. More than half of the trials used general anaesthesia. Surgical procedures in most trials were at low to moderate risk for perioperative cardiac complications. Only two comparisons including three studies reported the primary outcome - all-cause mortality up to 30 days post operation. Researchers reported other morbidity outcomes and adverse events in a variable and heterogeneous way, resulting in limited available data for inclusion in the meta-analysis. We determined that the overall methodological quality of included studies was fair to low, in accordance with risk of bias in most domains.In summary, we found no difference in the primary outcome - all-cause mortality up to 30 days post operation - when nitroglycerin was compared with no treatment (one study, 60 participants, 0/30 vs 1/30; (risk ratio (RR) 0.33, 95% confidence interval (CI) 0.01 to 7.87, very low-quality evidence based on GRADE criteria) or with placebo (two studies, 89 participants, 1/45 vs 0/44; RR 2.81, 95% CI 0.12 to 63.83, very low-quality evidence). Regarding our secondary outcomes, we noted no statistically significant differences in angina pectoris, acute myocardial infarction, acute heart failure, cardiac arrhythmia or cardiac arrest in any comparisons. In comparisons versus nitroglycerin, although more events of cardiac ischaemia were observed in participants receiving no treatment or placebo, we found no statistically significant differences in any comparisons, except the comparison of nicorandil versus placebo. One study revealed a potential dose-dependent protective effect of nicorandil for cardiac ischaemia.Adverse events were reported in a heterogeneous way among the comparisons. In general, more participants treated with nitrates had hypotension, tachycardia and headache, but investigators reported no statistically significant differences between groups in any comparisons.

AUTHORS' CONCLUSIONS

This systematic review suggests that nitroglycerin or isosorbide dinitrate is not associated with improvement in mortality and cardiac complications among patients undergoing non-cardiac surgery. Limited evidence suggests that nicorandil may reduce the risk of cardiac ischaemia in participants undergoing non-cardiac surgery. Additional studies are needed to consolidate the evidence.However, the data included in many of the analyses in this review are sparse - that is, adequate data are few - resulting in very low power to detect differences between nitrates and comparators. Thus, a more objective conclusion would state that available evidence is insufficient to show whether nitrates are associated with improvement in mortality and cardiac complications among patients undergoing non-cardiac surgery.Over the past decade, no high-quality studies have focused on association of cardiac mortality and morbidity with use of nitrates during non-cardiac surgery. This review underlines the need for well-designed trials in this field.

Organic Nitrate Therapy, Nitrate Tolerance, and Nitrate-Induced Endothelial Dysfunction: Emphasis on Redox Biology and Oxidative Stress

Organic nitrates, such as nitroglycerin (GTN), isosorbide-5-mononitrate and isosorbide dinitrate, and pentaerithrityl tetranitrate (PETN), when given acutely, have potent vasodilator effects improving symptoms in patients with acute and chronic congestive heart failure, stable coronary artery disease, acute coronary syndromes, or arterial hypertension. The mechanisms underlying vasodilation include the release of •NO or a related compound in response to intracellular bioactivation (for GTN, the mitochondrial aldehyde dehydrogenase [ALDH-2]) and activation of the enzyme, soluble guanylyl cyclase. Increasing cyclic guanosine-3',-5'-monophosphate (cGMP) levels lead to an activation of the cGMP-dependent kinase I, thereby causing the relaxation of the vascular smooth muscle by decreasing intracellular calcium concentrations. The hemodynamic and anti-ischemic effects of organic nitrates are rapidly lost upon long-term (low-dose) administration due to the rapid development of tolerance and endothelial dysfunction, which is in most cases linked to increased intracellular oxidative stress. Enzymatic sources of reactive oxygen species under nitrate therapy include mitochondria, NADPH oxidases, and an uncoupled •NO synthase. Acute high-dose challenges with organic nitrates cause a similar loss of potency (tachyphylaxis), but with distinct pathomechanism. The differences among organic nitrates are highlighted regarding their potency to induce oxidative stress and subsequent tolerance and endothelial dysfunction. We also address pleiotropic effects of organic nitrates, for example, their capacity to stimulate antioxidant pathways like those demonstrated for PETN, all of which may prevent adverse effects in response to long-term therapy. Based on these considerations, we will discuss and present some preclinical data on how the nitrate of the future should be designed.

Efficacy of the long-acting nitro vasodilator pentaerithrityl tetranitrate in patients with chronic stable angina pectoris receiving anti-anginal background therapy with beta-blockers: a 12-week, randomized, double-blind, placebo-controlled trial

Background

The organic nitrate pentaerithrityl tetranitrate (PETN) has been shown to have ancillary properties that prevent the development of tolerance and endothelial dysfunction. This randomized, double-blind, placebo-controlled, multicentre study (‘CLEOPATRA’ study) was designed to investigate the anti-ischaemic efficacy of PETN 80 mg b.i.d. (morning and mid-day) over placebo in patients with chronic stable angina pectoris.

Methods and results

A total of 655 patients were evaluated in the intention-to-treat population, randomized to PETN (80 mg b.i.d., n = 328) or placebo (n = 327) and completed the study. Patients underwent treadmill exercise tests at randomization, after 6 and 12 weeks of treatment. Treatment with PETN over 12 weeks did not modify the primary endpoint total exercise duration (TED, P = 0.423). In a pre-specified sub-analysis of patients with reduced exercise capacity (TED at baseline ≤9 min, n = 257), PETN appeared more effective than placebo treatment (P = 0.054). Superiority of PETN over placebo was evident in patients who were symptomatic at low exercise levels (n = 120; P = 0.017). Pentaerithrityl tetranitrate 80 mg b.i.d. was well tolerated, and the overall safety profile was comparable with placebo.

Conclusion

Although providing no additional benefit in unselected patients with known coronary artery disease, PETN therapy, administered in addition to modern anti-ischaemic therapy, could increase exercise tolerance in symptomatic patients with reduced exercise capacity.

Conventional and novel drug therapeutics to relief myocardial ischemia

Effective management of stable angina usually includes drug therapy. There are several agents that are considered vasculoprotective such as aspirin, angiotensin converting enzyme inhibitors and statins. Conventional anti ischemic therapy includes nitrates, beta-blockers and calcium-channel blockers. In recent years, several other drugs with novel anti ischemic mechanisms have become available including ranolazine, ivabradine, nicorandil and many others. This article reviews drugs that alleviate the symptoms of chronic angina with emphasis on several novel pharmacological agents.

Transdermal nitroglycerin as an adjuvant to patient-controlled morphine analgesia after total knee arthroplasty

BACKGROUND

Nitroglycerin (NTG) has been shown to be a useful adjunct for pain treatment without increasing adverse side effects. The effects of NTG on postoperative morphine consumption after knee replacement were evaluated.

METHODS

After undergoing total knee replacement, patients receiving patient-controlled morphine analgesia were randomly assigned to receive either an NTG or a placebo patch. The blinded investigator assessed each patient using a visual analogue scale at rest and while moving, as well as the patient's morphine requirements, sedation score, sleep quality, nausea and vomiting, vital signs and postoperative bleeding.

RESULTS

Two of the patients in the NTG group suffered postoperative myocardial infarctions after removal of the patch. Because of these two serious adverse effects, the study was stopped prematurely. In the subset of patients studied, NTG conferred no advantage over placebo in pain control (visual analogue scale at rest or during movement) and in satisfaction scores.

CONCLUSIONS

The use of NTG patches conferred no advantage over the use of placebo in patients receiving patient-controlled morphine analgesia after total knee replacement. Two myocardial infarcts occurred in this group. Therefore, the safety of postoperative NTG patch use for pain control must be questioned.

Possible usefulness of apocynin, an NADPH oxidase inhibitor, for nitrate tolerance: prevention of NO donor-induced endothelial cell abnormalities

The long-term benefits of nitroglycerin therapy are limited by tolerance development. Understanding the precise nature of mechanisms underlying nitroglycerin-induced endothelial cell dysfunction may provide new strategies to prevent tolerance development. In this line, we tested interventions to prevent endothelial dysfunction in the setting of nitrate tolerance. When bovine aortic endothelial cells (BAECs) were continuously treated with nitric oxide (NO) donors, including nitroglycerin, over 2-3 days, basal production of nitrite and nitrate (NO(x)) was diminished. The diminished basal NO(x) levels were mitigated by intermittent treatment allowing an 8-h daily nitrate-free interval during the 2- to 3-day treatment period. Addition of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor apocynin restored the basal levels of NO(x) that were decreased by continuous nitroglycerin treatment of BAECs. Apocynin caused significant improvement of increased mRNA and protein levels of endothelial nitric oxide synthase (eNOS) in BAECs given nitroglycerin continuously over the treatment period. Apocynin also reduced endothelial production of reactive oxygen species (ROS) after continuous nitroglycerin treatment. These results showed an essential similarity to the effects of a nitrate-free interval. Application of the NOS inhibitor N(omega)-nitro- l-arginine methyl ester caused a recovery effect on basal NO(x) and eNOS expression but was without effect on ROS levels in continuously NO donor-treated BAECs. In conclusion, the present study characterized abnormal features and functions of endothelial cells following continuous NO donor application. We suggest that inhibition of NADPH oxidase, by preventing NO donor-induced endothelial dysfunction, may represent a potential therapeutic strategy that confers protection from nitrate tolerance development.

Value and limitations of ambulatory ECG monitoring for assessment of myocardial ischemia

Ambulatory ECG monitoring (AEM) is the only available method to assess the presence and severity of myocardial ischemia during daily life. Several investigators have shown that the recording systems currently used can detect ischemic changes with similar accuracy as treadmill exercise testing. Ischemic changes on AEM are, however, present in only 40%-60% of patients with coronary artery disease (CAD) and positive exercise tests. For this reason, and because of the high day-to-day variability in daily ischemic changes, AEM cannot be used as a screening tool for detecting CAD or for evaluating severity of ischemia in individual patients. In patients with proven CAD, ischemic changes on AEM are associated with an adverse outcome in patients with stable and unstable ischemic syndromes, and in postmyocardial infarction patients. Suppression of daily ischemia seems to be associated with improved outcome. The mechanism of daily ischemia is not identical to exercise-induced ischemia. In addition to increased demand, which is a major contributor to AEM detected-ischemia, increased coronary tone also seems to play a major role. AEM has been shown to be a useful and reliable tool to assess the efficacy of various antiischemic drugs.

WITHDRAWAL OF INTRAVENOUS GLYCERYL TRINITRATE: ABSENCE OF REBOUND PHENOMENA WITH TRANSITION TO ORAL ISOSORBIDE DINITRATE

1. Glyceryl trinitrate (GTN) is frequently infused intravenously as a component of the management of acute coronary syndromes (ACS). Abrupt cessation of GTN infusion after periods of more than 24 h administration often induces rebound vasoconstriction reflecting 'pseudotolerance'; this is also the basis of the 'zero hour phenomenon' during chronic nitrate therapy. The efficacy of oral nitrate regimens to prevent vasoconstriction following cessation of intravenous GTN has not been previously examined. Therefore, we investigated the effects of transition from intravenous GTN to oral isosorbide dinitrate (ISDN) on a parameter of apparent arterial stiffness in patients with ACS. 2. The effects of GTN infusion at 5 microg/min on augmentation index (AIx) were quantified in patients (n = 10) with stable angina pectoris in order to establish the magnitude of effect on apparent arterial stiffness. 3. This infusion rate of GTN reduced AIx from 23 +/- 10% (SD) to 3 +/- 14% (SD) (P < 0.01). The effect of transition from GTN infusion of greater than 24 h duration to ISDN (10 mg tds) were examined in patients (n = 16) with ACS (unstable angina/non-Q-wave myocardial infarction). No patient developed recurrent angina during the 24 h following cessation of GTN infusion. The level of AIx was 8 +/- 4% (SD) prior to GTN cessation and fell to 5 +/- 6% (SD) on ISDN (P = 0.05). 4. Thus, in patients treated for ACS, transition from intravenous GTN to low dose oral ISDN is associated with an incremental vasodilatation and no evidence of 'rebound' ischaemia.

Clinical pharmacokinetics and pharmacodynamics of glyceryl trinitrate and its metabolites

This review discusses the pharmacokinetics and pharmacodynamics of glyceryl trinitrate (nitroglycerin; GTN) pertinent to clinical medicine. The pharmacokinetics of GTN associated with various dose regimens are characterised by prominent intra- and inter-individual variability. It is, nevertheless, important to clearly understand the pharmacokinetics and characteristics of GTN to optimise its use in clinical practice and, in particular, to obviate the development of tolerance. Measurements of plasma concentrations of GTN and of 1,2-glyceryl dinitrate (1,2-GDN), 1,3-glyceryl dinitrate (1,3-GDN), 1-glyceryl mononitrate (1-GMN), and 2-glyceryl mononitrate (2-GMN), its four main metabolites, remain difficult and require meticulous techniques to obtain reliable results. Since GDNs have an effect on haemodynamic function, pharmacokinetic analyses that include the parent drug as well as the metabolites are important. Although the precise mechanisms of GTN metabolism have not been elucidated, two main pathways have been proposed for its biotransformation. The first is a mechanism-based biotransformation pathway that produces nitric oxide (NO) and contributes directly to vasodilation. The second is a clearance-based biotransformation or detoxification pathway that produces inorganic nitrite anions (NO(2) -). NO(2) - has no apparent cardiovascular effect and is not converted to NO in pharmacologically relevant concentrations in vivo. In addition, several non-enzymatic and enzymatic systems are capable of metabolising GTN. This complex metabolism complicates considerably the evaluation of the pharmacokinetics and pharmacodynamics of GTN. Regardless of the route of administration, concentrations of the metabolites exceed those of the parent compound by several orders of magnitude. During continuous steady-state delivery of GTN, for instance by a patch, concentrations of 1,2-GDN are consistently 2-7 times higher than those of 1,3-GDN, and concentrations of 2-GMN are 4-8 times higher than those of 1-GMN. Concentrations of GDNs are approximately 10 times higher, and of GMNs approximately 100 times higher, than those of GTN during sustained administration. The development of tolerance is closely related to the metabolism of GTN, and can be broadly categorised as haemodynamic tolerance versus vascular tolerance. Efforts are warranted to circumvent the development of tolerance and facilitate the use of GTN in clinical practice. Although this remains to be accomplished, it is likely that, in the near future, regimens will be developed based on a full understanding of the pharmacokinetics and pharmacodynamics of GTN and its metabolites.

Mechanisms underlying nitrate-induced endothelial dysfunction: insight from experimental and clinical studies

The hemodynamic and anti-ischemic effects of nitroglycerin (NTG) are rapidly blunted due to the development of nitrate tolerance. With initiation of nitroglycerin therapy one can detect neurohormonal activation and signs for intravascular volume expansion. These so called pseudotolerance mechanisms may compromise nitroglycerin's vasodilatory effects. Long-term treatment with nitroglycerin is also associated with a decreased responsiveness of the vasculature to nitroglycerin's vasorelaxant potency suggesting changes in intrinsic mechanisms of the tolerant vasculature itself may also contribute to tolerance. More recent experimental work defined new mechanisms of tolerance such as increased vascular superoxide production and increased sensitivity to vasoconstrictors secondary to an activation of the intracellular second messenger protein kinase C. As potential superoxide producing enzymes, the NADPH oxidase and the nitric oxide synthase have been identified. Nitroglycerin-induced stimulation of oxygen-derived free radicals together with NO derived from nitroglycerin may lead to the formation of peroxynitrite, which may be responsible for the development of tolerance as well as for the development of cross tolerance to endothelium-dependent vasodilators. The oxidative stress concept of tolerance and cross tolerance may explain why radical scavengers such as vitamin C or substances which reduce oxidative stress, such as ACE-inhibitors, AT1 receptor blockers or folic acid, are able to beneficially influence both tolerance and nitroglycerin-induced endothelial dysfunction. New aspects concerning the role of oxidative stress in nitrate tolerance and nitrate induced endothelial dysfunction and the consequences for the NO/cyclicGMP downstream target, the cGMP-dependent protein kinase will be discussed.

Paradigm shifts in clinical trials enabled by information technology

The use of the world wide web for clinical trials changes the processes of performing clinical research in several fundamental ways. Greatly improved security, monitoring capability, and accuracy and timeliness of study conduct can be achieved while lowering cost. Data quality is enhanced while co-ordinating centre effort is reduced. The web provides a natural environment for linking the various components of clinical research, leading to new levels of simplicity and efficiency. It also enhances opportunities for recruitment of study investigators and patients. Other information technology tools and databases can be used to assist in this regard as well. Web-based trials change the relationship of the investigator site to the study and the site to the co-ordinating centre. Different roles and responsibilities lead to simplified processes and more and higher quality data. Many standard co-ordinating centre activities, such as randomization, protocol implementation and amending, document tracking, adverse event reporting, site monitoring, report generation and data analysis are all fundamentally changed in a web-based trial. Opportunities are enhanced to identify potential investigators and support their successful study conduct. As the role of investigator sites is changed in web-based research, more primary care medical providers can be attracted to research, providing more typical patients to studies than those sometimes available through more traditional research sites, especially those at academic study sites. Other activities can now be co-ordinated electronically with the advent of the web. The Institutional Review Board (IRB) can use online tools to control investigator participation, resulting in improved study efficiency and patient safety. A web-based research pharmacy provides tremendous efficiencies in managing and distributing study medications. Financial payments to the sites can be performed and recorded electronically, or even administered based on timeliness and quality of the data. Our early experience with web-based trials indicates that there can be tremendous gains in study efficiency and accuracy by restructuring processes, roles and responsibilities through a comprehensive centralized, web-based trial. The future appears bright for web-based clinical trials.

Nitroglycerin withdrawal increases endothelium-dependent vasomotor response to acetylcholine

OBJECTIVES

We sought to determine whether nitroglycerin (NTG) withdrawal contributes to worsening of endothelial dysfunction and development of the rebound phenomenon during intermittent transdermal NTG therapy.

BACKGROUND

Intermittent transdermal NTG therapy is recommended to avoid the development of tolerance. However, this regimen may precipitate worsening angina in the NTG-free interval.

METHODS

Twenty patients were randomized to intermittent transdermal NTG (0.6 mg/h; NTG group) or no treatment (control group) five days before angiography. The risk factors for endothelial dysfunction were similar in both groups. After diagnostic angiography, the patients underwent quantitative angiography before and after intracoronary acetylcholine (ACh), 10(-4) mol/liter. Immediately after the morning study, the patch was removed from the NTG group, and 3 h later, the ACh infusion was repeated in both groups. All patients had mild to moderate coronary artery disease (CAD).

RESULTS

The diameter of the left anterior descending coronary artery at baseline was 2.0 +/- 0.1 mm in the control group and 2.6 +/- 0.1 mm in the NTG group (p < 0.05). Acetylcholine caused mild vasoconstriction in the control group in the morning and afternoon (2.7 +/- 5.3% and 2.4 +/- 3.9%, respectively; p = NS). The NTG group demonstrated mild vasoconstriction to ACh in the morning (3.2 +/- 2.8%; p = NS vs. control group). After patch removal, there was a significant increase in the magnitude ofvasoconstriction in the NTG group (11.6 +/- 3.9%, p = 0.04 vs. morning constriction).

CONCLUSIONS

These results confirm that NTG withdrawal increases the coronary vasomotor response to ACh in patients with mild CAD and suggests that the rebound phenomena may be secondary to the development of endothelial dysfunction after discontinuation of NTG therapy.

The pharmacokinetics of trinitroglycerin and its metabolites in patients with chronic stable angina

AIMS

To study the pharmacokinetics of trinitroglycerin (GTN) and its four metabolites in angina patients during their transient use of transdermal GTN tape following intravenous administration of GTN.

METHODS

Four patients received a GTN tape following intravenous administration of 0.1 microg kg-1 min-1 GTN, and the other four patients received two GTN tapes following intravenous administration of 0.2 microg kg-1 min-1 GTN.

RESULTS

Plasma concentrations of GTN in both groups during tape application showed a slight decrease for the hour after the application of the tape and then were con- stant for 24 h. In contrast, the concentrations of dinitroglycerins (GDNs) and mononitroglycerins (GMNs) depended on the duration of previous intravenous administration of GTN. Neither significant cardiovascular changes nor undesirable complications were observed during the study.

CONCLUSIONS

The results suggest that appropriate replacement of intravenous GTN administration with transdermal tape application could maintain a therapeutic GTN level.

Effects of a nitrate-free interval on tolerance, vasoconstrictor sensitivity and vascular superoxide production

OBJECTIVES

In the present study, we tested whether a nitrate-free interval is able to prevent increases in vascular superoxide (O2*-) and the development of hypersensitivity to vasoconstrictors and whether this may result in restoration of vascular nitroglycerin (NTG) sensitivity.

BACKGROUND

Intermittent NTG-patch treatment (12 h patch on/patch-off) has been shown to increase ischemic periods in patients with stable coronary arteries, suggesting a rebound-like situation during the patch-off period. Recently, we demonstrated that long-term treatment with NTG induces tolerance, which was in part related to increases in vascular O2*- and increased vasoconstrictor sensitivity.

METHODS

New Zealand white rabbits received a continuous application of NTG patches (0.4 mg/h) or an intermittent application of NTG patches (12 h patch on, 12 h patch off) for three days. Isometric tension studies were performed with aortic rings, and vascular O2*- was estimated using lucigenin-derived chemiluminescence (5 micromol/liter). Expression of the copper/zinc (Cu/Zn) superoxide dismutase (SOD) was assessed by Western blotting, and SOD activity was measured by autooxidation of 6-hydroxydopamine.

RESULTS

Continuous treatment with NTG caused tolerance to NTG, cross-tolerance to the endothelium-dependent vasodilator acetylcholine, increased vascular O2*-, reduced Cu/Zn SOD expression and increased sensitivity to vasoconstrictors such as phenylephrine, serotonin and angiotensin II. On/off treatment with NTG improved tolerance, corrected endothelial dysfunction and decreased vascular O2*-. In addition the reduction in SOD expression was less pronounced, whereas increases in the sensitivity to vasoconstrictors such as phenylephrine and serotonin remained nearly unchanged.

CONCLUSIONS

Enhanced vasoconstrictor sensitivity may explain, at least in part, the rebound phenomena observed in patients during a 12-h NTG patch-off period.

Optimal nitrate therapy with a once-daily sustained-release formulation of isosorbide mononitrate

During long-term prophylaxis of angina with oral nitrates, sustained high plasma nitrate concentrations produce partial or complete tolerance to both the haemodynamic and the clinical effects of the drug. There is substantial evidence that this can be prevented by an adequate nitrate-free or nitrate-low period during each 24 h dosing interval. However, a nitrate-free interval carries the risk of a rebound increase in myocardial ischaemia. Once-daily formulations of isosorbide mononitrate deliver high plasma nitrate concentrations that improve exercise tolerance in patients with angina for at least 12 h after dosing. During the remainder of the dosage interval, plasma nitrate concentrations fall but are sufficient to protect against coronary artery spasm overnight. Myocardial ischaemia has a marked circadian rhythm. All ischaemic events (total ischaemic burden, myocardial infarction and sudden cardiac death) are most frequent in the hours immediately after waking. Oral anti-ischaemic prophylaxis should ideally provide protection during this critical period, in order to minimize symptoms, maximize exercise capacity and perhaps also to reduce the risk of clinical events. The ideal long-acting nitrate formulation should therefore provide a rapid rise in plasma nitrate concentration as well as maintaining prolonged efficacy throughout the dosing interval. Elantan LA is a sustained-release capsule formulation of isosorbide mononitrate for once-daily dosing. This capsule contains pellets which release 30% of the dose immediately, while 70% is released slowly to maintain the therapeutic response. The pharmacokinetic profile of this formulation prevents the development of tolerance, while also conferring long-term anti-anginal efficacy. Patients reported an improvement in both severity of angina and quality of life indices when their therapy was changed from multiple daily dosing with isosorbide dinitrate to once-daily dosing with Elantan LA (50 mg). The anti-anginal effect of Elantan LA is attained rapidly after dosing. Within 30 min of ingestion, there are clinically significant improvements in exercise tolerance, comparable with the speed of onset after an immediate-release formulation of isosorbide mononitrate. Elantan LA is an effective once-daily prophylaxis for angina which also produces a rapid onset of therapeutic effect. The release profile of this formulation maximizes protection against the morning surge in myocardial ischaemia.

Attenuation of anti-ischemic efficacy during chronic therapy with nicorandil in patients with stable angina pectoris

After 2 weeks of nicorandil therapy, time to ischemia on stress testing was significantly less than on day 1 and not different from placebo. These data are consistent with attenuation of the anti-ischemic effects of this drug and suggest that the potassium channel-opening properties do not compensate for development of attenuation to the nitrate component of nicorandil.