Avoidance of tolerance and lack of rebound with intermittent dose titrated transdermal glyceryl trinitrate. The Transdermal Nitrate Investigators

Nicorandil and Long-acting Nitrates: Vasodilator Therapies for the Management of Chronic Stable Angina Pectoris

Nicorandil and long-acting nitrates are vasodilatory drugs used commonly in the management of chronic stable angina pectoris. Both nicorandil and long-acting nitrates exert anti-angina properties via activation of nitric oxide (NO) signalling pathways, triggering vascular smooth muscle cell relaxation. Nicorandil has additional actions as an arterial K⁺ _ATP channel agonist, resulting in more "balanced" arterial and venous vasodilatation than nitrates. Ultimately, these drugs prevent angina symptoms through reductions in preload and diastolic wall tension and, to a lesser extent, epicardial coronary artery dilatation and lowering of systemic blood pressure. While there is some evidence to suggest a modest reduction in cardiovascular events among patients with stable angina treated with nicorandil compared to placebo, this prognostic benefit has yet to be proven conclusively. In contrast, there is emerging evidence to suggest that chronic use of long-acting nitrates might cause endothelial dysfunction and increased cardiovascular risk in some patients.

The Role of Nitroglycerin and Other Nitrogen Oxides in Cardiovascular Therapeutics

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

Vasodilator Therapy: Nitrates and Nicorandil

Nitrates have been used to treat symptoms of chronic stable angina for over 135 years. These drugs are known to activate nitric oxide (NO)-cyclic guanosine-3',-5'-monophasphate (cGMP) signaling pathways underlying vascular smooth muscle cell relaxation, albeit many questions relating to how nitrates work at the cellular level remain unanswered. Physiologically, the anti-angina effects of nitrates are mostly due to peripheral venous dilatation leading to reduction in preload and therefore left ventricular wall stress, and, to a lesser extent, epicardial coronary artery dilatation and lowering of systemic blood pressure. By counteracting ischemic mechanisms, short-acting nitrates offer rapid relief following an angina attack. Long-acting nitrates, used commonly for angina prophylaxis are recommended second-line, after beta-blockers and calcium channel antagonists. Nicorandil is a balanced vasodilator that acts as both NO donor and arterial K(+) ATP channel opener. Nicorandil might also exhibit cardioprotective properties via mitochondrial ischemic preconditioning. While nitrates and nicorandil are effective pharmacological agents for prevention of angina symptoms, when prescribing these drugs it is important to consider that unwanted and poorly tolerated hemodynamic side-effects such as headache and orthostatic hypotension can often occur owing to systemic vasodilatation. It is also necessary to ensure that a dosing regime is followed that avoids nitrate tolerance, which not only results in loss of drug efficacy, but might also cause endothelial dysfunction and increase long-term cardiovascular risk. Here we provide an update on the pharmacological management of chronic stable angina using nitrates and nicorandil.

Challenges with nitrate therapy and nitrate tolerance: prevalence, prevention, and clinical relevance

Nitrate therapy has been an effective treatment for ischemic heart disease for over 100 years. The anti-ischemic and exercise-promoting benefits of sublingually administered nitrates are well established. Nitroglycerin is indicated for the relief of an established attack of angina and for prophylactic use, but its effects are short lived. In an effort to increase the duration of beneficial effects, long-acting orally administered and topical applications of nitrates have been developed; however, following their continued or frequent daily use, patients soon develop tolerance to these long-acting nitrate preparations. Once tolerance develops, patients begin losing the protective effects of the long-acting nitrate therapy. By providing a nitrate-free interval, or declining nitrate levels at night, one can overcome or reduce the development of tolerance, but cannot provide 24-h anti-anginal and anti-ischemic protection. In addition, patients may be vulnerable to occurrence of rebound angina and myocardial ischemia during periods of absent nitrate levels at night and early hours of the morning, and worsening of exercise capacity prior to the morning dose of the medication. This has been a concern with nitroglycerin patches but not with oral formulations of isosorbide-5 mononitrates, and has not been adequately studied with isosorbide dinitrate. This paper describes problems associated with nitrate tolerance, reviews mechanisms by which nitrate tolerance and loss of efficacy develop, and presents strategies to avoid nitrate tolerance and maintain efficacy when using long-acting nitrate formulations.

Tolerance to the Therapeutic Effect of Tadalafil Does Not Occur During 6 Months of Treatment: A Randomized, Double‐Blind, Placebo‐Controlled Study in Men with Erectile Dysfunction

INTRODUCTION

Tolerance can cause a decrease in drug efficacy during chronic therapy, possibly leading to treatment failures.

AIM

The aim of this article is to determine whether tolerance developed to the effects of tadalafil on erectile function (EF) over a 6-month treatment period.

METHODS AND MAIN OUTCOME MEASURES

Post hoc analysis of data from a multicenter, double-blind, randomized, placebo-controlled, parallel group study was performed. Men (> or =18 years of age) with erectile dysfunction (ED) were randomized to treatment with placebo (N = 47) or 20-mg tadalafil (N = 93) taken as needed for 6 months. This report focuses on efficacy assessed with the Sexual Encounter Profile (SEP) diary (diaries were collected after a 4-week treatment-free run-in period [baseline], and monthly for 6 months), and with the International Index of Erectile Function (IIEF) (administered at baseline, and at 3 and 6 months). RESULTS. The mean per-patient percentage "yes" response on SEP question 3 (SEP3, successful intercourse) was 33 +/- 4% at baseline, 74 +/- 4% after 1 month, and 78 +/- 4% after 6 months of tadalafil treatment. The IIEF EF domain score was 16.2 +/- 0.7 at baseline, 24.3 +/- 0.8 after 3 months, and 24.3 +/- 0.9 after 6 months of tadalafil treatment. In a subgroup of patients who took tadalafil > or =3 times per week (N = 24), the SEP3 score was 87 +/- 4% after 1 month and 93 +/- 3% after 6 months of treatment, and the IIEF EF domain score was 27.3 +/- 0.9 after 3 months and 28.5 +/- 0.4 after 6 months. Of 16 tadalafil-treated patients who discontinued, three cited a lack of efficacy.

CONCLUSIONS

Tadalafil treatment significantly improved SEP3 and IIEF EF domain scores. The efficacy of tadalafil, taken as needed, was maintained over a 6-month treatment period in men with ED.

Eccentric Dosing of Nitrates Does Not Increase Cardiac Events in Patients with Healed Myocardial Infarction

This study was performed to investigate the risk of cardiac events by eccentric or continuous dosing of nitrates in patients with healed myocardial infarction. A total of 573 patients with healed myocardial infarction were assigned to one of two groups: a nitrate-treatment (n =239) and a nontreatment (n =334) group. The nitrate-treatment group was further subdivided into a group receiving eccentric dosing of nitrates (n =153) and a group receiving continuous dosing of nitrates (n =86). The mean observation period was 11.2+/-8.2 months. The cardiac events investigated were nonfatal and fatal recurrent myocardial infarction, death from congestive heart failure, sudden death, worsening angina and rebound angina. Baseline characteristics were also compared among the three groups to determine any effects on outcome. Among the patients receiving eccentric or continuous dosing of nitrates, the rates of cardiac events were 12.7/1,000 person.year and 67.4/1,000 person.year, respectively, whereas the rate was 19.7/1,000 person.year in the nontreated patients. The incidence of cardiac events was significantly greater in patients receiving continuous dosing of nitrates than in the nontreated patients (p <0.05). Continuous dosing of nitrates thus increases cardiac events, and while eccentric dosing of nitrates does not increase them, it is also not effective at preventing them in patients with healed myocardial infarction.

Nitroglycerin rebound associated with vascular, rather than platelet, hypersensitivity

OBJECTIVES

The purpose of this study was to determine whether acute withdrawal of nitroglycerin (NTG) during hemodynamic tolerance is associated with platelet hypersensitivity.

BACKGROUND

Nitroglycerin is an effective antianginal medication but its use is limited by the development of tolerance and rebound. We have previously demonstrated a sustained inhibition of platelet function during continued use of NTG, but whether cessation of NTG is associated with an increase in platelet function that may contribute to rebound is unknown.

METHODS

Normal porcine aortic media were exposed to flowing arterial blood from pigs (n = 8) treated continuously with NTG patches (Nitrodur 0.8 mg/h) for 48 h. Platelet function, blood pressure and the responses to angiotensin II infusion were evaluated before, during and after NTG treatment.

RESULTS

Mean arterial pressure fell by 15% after 3 h of treatment compared with control, returned to baseline by 48 h and increased significantly 2 h after drug removal. Autologous 51Cr-labelled platelet deposition on the aortic media was reduced by 30% after 48 h of continuous NTG administration compared with baseline (p = 0.02) and remained decreased 2 h after cessation of NTG therapy. Platelet aggregation to thrombin decreased in parallel to the decrease in platelet deposition. Blood pressure increase after intravenous injection of 10 microg of angiotensin II was blunted during treatment with NTG but increased significantly 2 h after cessation of nitrate therapy when compared with baseline.

CONCLUSIONS

Supersensitivity of the vessel wall to vasoconstrictors such as angiotensin 11, but not platelet hyperactivity, may contribute to the rebound phenomenon after acute nitrate withdrawal.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

OBJECTIVES

We sought to evaluate the effects of intermittent transdermal nitroglycerin (TD-NTG) on the occurrence of ischemia during patch-off hours in patients with stable angina pectoris receiving a beta-adrenergic blocking agent or calcium antagonist, or both.

BACKGROUND

The current recommendations for the use of intermittent TD-NTG may be associated with the occurrence of rebound ischemia.

METHODS

This was a multicenter, randomized, double-blind, placebo-controlled, crossover trial with three study periods. Tolerability to TD-NTG was assessed in Period I. Seventy-two patients were assigned to receive either double-blind transdermal placebo or maximally tolerated TD-NTG for 2 weeks (Period II) and were then crossed over to the alternative treatment for another 2 weeks (Period III). The patients were instructed to apply medication daily at 8 AM, to remove it at 10 PM and to note symptoms and sublingual nitroglycerin (SL-NTG) use in a diary. The occurrence of ischemia was assessed from patient-perceived angina, symptom-limited exercise treadmill test (ETT) and 48-h ambulatory electrocardiographic (AECG) monitoring.

RESULTS

Transdermal NTG (0.2 to 0.4 mg/h) significantly reduced the magnitude of ST segment depression at angina onset during ETT compared with placebo. Total angina frequency was not significantly different between TD-NTG (mean [+/-SD] 3.2 +/- 4.2) and placebo (3.3 +/- 5.2). During patch-off hours, angina frequency increased with TD-NTG (1.1 +/- 2.1) compared with placebo (0.7 +/- 1.6) (p = 0.03). Similar trends for an increase in ischemia after TD-NTG were also observed from AECG analyses. Specifically, ischemia frequency tended to be lower during patch-off hours for placebo than with TD-NTG (0.05 +/- 0.09 vs. 0.08 +/- 0.20 episodes/h, respectively, p = 0.08), even though frequency of ischemia tended to be higher during patch-on hours for placebo than with TD-NTG (0.12 +/- 0.19 vs. 0.07 +/- 0.15 episodes/h, respectively, p = 0.11). During placebo, ischemia frequency decreased 58% (patch-on to patch-off, p = 0.01) compared with a 14% increase with TD-NTG. These changes attenuate the usual circadian variation in ischemia.

CONCLUSIONS

An increase in ischemia frequency during patch-off hours after use of intermittent TD-NTG was perceived by patients, and this subjective finding was supported by a corresponding trend for AECG ischemia to increase during these same hours.

Achieving sustained improvement in myocardial perfusion: role of isosorbide mononitrate

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

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

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

Contemporary approaches in medical management of patients with stable coronary artery disease

CAD continues to be the principal cause of mortality in the United States, and the largest group of patients with CAD are those with stable angina. Among this group of patients, the most common manifestation of CAD is presence of transient episodes of myocardial ischemia. The presence of transient ischemia and not the severity of angina has been found to be associated with poor clinical outcome in patients with stable CAD. As part of a global treatment strategy for patients with stable CAD, changes in lifestyle and modification of coronary risk factors should be emphasized as an integral part of treatment. Conventional antianginal therapy is quite effective in controlling anginal attacks. Currently, several drugs and therapeutic strategies are available for the treatment of patients with angina (see Table 5). Nitrates are highly effective antianginal drugs with complex beneficial actions in patients with CAD, but their usefulness is limited by development of tolerance during long-term use. When clinically indicated, the use of nitrates should be supplemented with another longer-acting antianginal drug, such as a beta-blocker or a calcium channel blocker. Based on the available data, beta-blockers, when tolerated, seem to be the most effective antianginal drugs for most patients with stable CAD. Beta-blockers are also the most effective anti-ischemic drugs that reduce the magnitude of myocardial ischemia detected during routine daily activities. Calcium channel blockers are also effective vasodilators and good antianginal drugs. The clinician should become familiar with the different actions that this heterogeneous group of drugs has on the heart and vessels. This knowledge allows the clinician to choose the appropriate combination of different antianginal drugs for patients on an individualized basis. It is also critical to develop the treatment strategy by carefully taking into account other associated medical conditions that are frequently encountered in patients with CAD.

Haemodynamic evaluation of two regimens of molsidomine in patients with chronic congestive heart failure

We investigated the extent and duration of the haemodynamic effects of two regimens of molsidomine, i.e. two tablets of a standard regimen consisting of 4 mg given 6 h apart and one tablet of 16 mg in sustained-release form once daily in 13 patients with chronic congestive heart failure using a placebo-controlled, randomized, double-blind and crossover protocol over a period of 12 h. Both regimens significantly affected systolic, mean and diastolic pulmonary arterial pressure (reductions of up to 15%), right atrial pressure (reductions of up to 35%) and total pulmonary resistance (reductions of up to 18%). The lower dose achieved its maximum action after about 1 h and remained effective for 2 h, whereas the higher dose in sustained-release form showed maximal efficacy at 2 h and remained active even at 12 h. In contrast, only minor changes in arterial blood pressure, systemic vascular resistance and cardiac output were observed on both regimens, almost exclusively at 2 h. Heart rate was not affected by either of the regimens tested. Neither regimen led to any untoward adverse effects. Thus, molsidomine is a potent vasodilating agent which, apart from its effects on preload, also acts on pulmonary arterial and right atrial pressures, leaving systemic circulation largely unaffected on the regimens tested. Administered on its own, it is therefore suitable for treatment of congestive heart failure.

Anti-ischemic effects of first and second dose of 20 mg isosorbide dinitrate administered 5 hours apart: attenuation of effects despite rising plasma concentration

Based on evidence that there may be early tolerance development even within the first daily cycle of treatment, this study was undertaken to evaluate the duration and extent of the antiischemic effects of two 20 mg doses of isosorbide dinitrate as used in a well-established regimen documented to maintain effectiveness during long-term treatment. Ischemia parameters were analyzed at 2 and 4 1/2 hours after the first dose as well as at 2 and 7 hours after the second dose given 5 hours later. The studies were performed in 10 male patients with documented coronary artery disease using bicycle ergometry and a double-blind, randomized, placebo-controlled, crossover protocol. ST-segment depression was reduced by 59% (p < 0.0005) at 2 hours and by 42% (p < 0.01) at 4 1/2 hours after the first tablet and by 38% (p < 0.005) at 2 hours and by 15% (p < 0.05) at 7 hours after the second tablet. Increments in ischemia-free workload capacity amounted to 112% (p < 0.005) and to 41% (p < 0.05) after the first tablet and 68% (p < 0.05) and 38% (p < 0.05) at 2 and 7 hours after the second tablet. At 2 and 4 1/2 hours after the first tablet, plasma concentrations of isosorbide dinitrate were 8.4 and 5.9 ng/ml, and those of isosorbide-5-mononitrate were 166.6 and 130.3 ng/ml. At 2 and 7 hours after the second tablet, the concentrations of isosorbide dinitrate were 9.1 and 5.9 ng/ml, and those of isosorbide-5-mononitrate were 224.5 and 148.1 ng/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Daily life cardiac ischaemia. Should it be treated?

Daily life cardiac ischaemia is defined as reversible myocardial cellular hypoxia that occurs during activities of daily living, without artificial provocation. Most of these daily life ischaemic episodes are not associated with symptoms. However, it is not practical to distinguish silent versus symptomatic daily life ischaemia as both are associated with haemodynamic abnormalities and future adverse outcomes. Daily life cardiac ischaemia is best detected using ambulatory electrocardiogram (ECG) monitoring; however, there are other diagnostic tools (e.g. exercise treadmill) that can be used. Once detected, the optimal therapy for daily life myocardial ischaemia has yet to be identified. However, it does appear that usual antianginal medications including nitrates, beta-blockers, calcium antagonists and antiplatelet drugs are effective in reducing the incidence and severity of daily life myocardial ischaemia. Medical therapy and revascularisation should be utilised to obliterate all episodes of daily life cardiac ischaemia to prevent future cardiac events. Moreover, the efficacy of the chosen therapeutic regimen for each patient should be documented with follow-up objective testing. The diagnosis and management of daily life myocardial ischaemia is continually evolving. Future research as well as economic considerations will shape future management strategies.

Intermittent transdermal nitrates do not improve ischemia in patients taking beta-blockers or calcium antagonists: potential role of rebound ischemia during the nitrate-free period

OBJECTIVES

This study was conducted to determine whether rebound ischemia occurs during nitrate-free periods with intermittent cutaneous nitroglycerin therapy in patients with angina pectoris who are receiving background antianginal therapy.

BACKGROUND

Rebound angina has been suggested to be a complication of the nitrate-free period with long-term cutaneous nitroglycerin therapy given intermittently to prevent tolerance.

METHODS

Fifty-two patients with stable effort angina taking either a beta-adrenergic blocking agent (n = 25) or diltiazem (n = 22) or their combination (n = 5) completed a randomized, double-blind, placebo-controlled crossover study of cutaneous nitroglycerin patches (50 mg). Active or placebo patches were worn for 1 week, applied at 8 AM and removed at 10 PM to provide a 10-h daily nitrate-free (or placebo-free) period. During the last 48 h of each study phase, a Holter monitor was used to detect ischemia.

RESULTS

Only 31 patients experienced ischemia during either phase of the study (23 during the patch-off period). A total of 463 ischemic episodes were recorded: 246 during placebo and 217 during nitroglycerin (p = 0.8, for per patient comparison). The majority (88%) of ischemic episodes were silent. Mean (+/- SEM) duration of ischemia during the total 48-h period was similar during active and placebo phases (35.5 +/- 15.0 min/24 h for active therapy vs. 29.7 +/- 9.8 for placebo, p = 0.8). This was due to an increase in duration of ischemia with active therapy during the patch-off period (46.9 +/- 17.9 min/24 h for active therapy vs. 22.5 +/- 9.2 for placebo, p = 0.07) and a decrease during the patch-on period (27.5 +/- 14.0 min/24 h for active therapy vs. 34.5 +/- 11.0 min/24 h for placebo, p = 0.16). The pattern of diurnal distribution of ischemic episodes differed between active and placebo phases. During placebo there was a nadir in the incidence of ischemia in the overnight patch-off period, with a significantly lower incidence between midnight and 6 AM (25 episodes) compared with the mean number of episodes during the three other 6-h periods (73 episodes, p < 0.001). During the nitroglycerin patch-off period, there was a loss of this overnight nadir, with the same incidence of ischemia between midnight and 6 AM (53 episodes) as the mean number of episodes for the three other 6-h periods (54 episodes).

CONCLUSIONS

The majority of patients taking background antianginal therapy experienced no ischemia during the patch-off period. In the 44% of patients with ischemia during this period, there was a nonsignificant increase in the duration of ischemia with active therapy. Although this result was statistically inconclusive, the change in the distribution of diurnal ischemia offers suggestive evidence that rebound ischemia may be a problem with regard to intermittent cutaneous nitroglycerin.

Which drug to choose for stable angina pectoris: a comparative study between bisoprolol and nitrates

The choice between beta-blockade or nitrates as first line treatment for stable angina pectoris is based upon the different mechanisms of action and patient characteristics. We performed a clinical trial comparing the efficacy of the longacting beta-blocker bisoprolol once daily and the short acting nitrate, isosorbide dinitrate, three times daily in the reduction of anginal complaints in daily life and under stress. Thirty patients were enrolled in a double-blind randomised cross-over study. Both bisoprolol and isosorbide dinitrate were effective in reducing anginal attacks and nitroglycerin consumption significantly, but bisoprolol was significantly more effective than isosorbide dinitrate. Bisoprolol improved the workload during bicycle exercise testing significantly, but the improvement with isosorbide dinitrate was not significant. Despite the reduction in maximal rate pressure product, bisoprolol was significantly (P < 0.05) more effective at improving total workload and reducing the time to onset of angina than isosorbide dinitrate. The rate pressure product did not change significantly with isosorbide dinitrate. In this study, bisoprolol 10 mg once daily was more effective and caused less side effects than isosorbide dinitrate 20 mg three times a day. It seems questionable if monotherapy of isosorbide dinitrate 20 mg t.i.d is an adequate drug regime for stable angina pectoris.

Nitrates in silent ischemia

In recent years it has become clear that episodes of transient myocardial ischemia commonly occur in patients with coronary artery disease in the absence of chest pain or angina equivalent. These episodes of "silent myocardial ischemia" are particularly well documented during continuous ambulatory electrocardiographic monitoring in daily life. Evidence suggests that these episodes represent true ischemia, and appear to be a marker of unfavorable outcome. While the pathophysiology is not completely understood, it appears as though the mechanisms of angina and silent ischemia are the same. Both forms of ischemia respond to conventional antianginal medication. While long-acting nitrates are effective in reducing or preventing myocardial ischemia, because of their propensity to cause tolerance they should be used intermittently and in association with either beta-blockers or calcium antagonists. Nitrates are safe and comparatively inexpensive, and will continue to play an important role in the treatment and prevention of angina. However, in the light of current knowledge, there is no specific indication for the treatment of silent ischemia by nitrates.

Ointments and transdermal nitroglycerin patches for stable angina pectoris

Nitroglycerin (NTG) ointment is used for the prophylaxis against angina pectoris, but there are no data to support its effectiveness during long-term therapy. Continuous, once-daily application of isosorbide dinitrate cream produces tolerance with complete loss of efficacy within 1 week. Nitroglycerin patches are very popular and continuous once-daily application is still claimed by some investigators to provide 24 hour antiischemic and antianginal efficacy. This claim is based on data from postmarketing studies in a very large number of patients and placebo-controlled studies in smaller groups of patients from Italy, Yugoslavia, Greece, and Germany. In contrast, studies from the United States, Canada, England, and some centers in Germany have failed to show superiority of patches over placebo during continuous therapy. This controversy was addressed by the NTG cooperative study group, in which a total of 562 patients who were responders to sublingual nitroglycerin were studied. Patients received either placebo or NTG patches delivering low (15-30 mg/24 hr), moderate (45-60 mg/24 hr), or large (75 and 105 mg/24 hr) amounts of NTG. Four hours after the initial application, NTG patches increased exercise duration compared to placebo, but this beneficial effect had disappeared by 24 hours. Furthermore, after 8 weeks of continuous therapy, none of the NTG patches were superior to placebo, whether patients were or were not taking concomitant beta-blockers. Therefore, current opinion is that continuous therapy with NTG patches produces pharmacologic tolerance and is ineffective.(ABSTRACT TRUNCATED AT 250 WORDS)

Risk of rebound phenomenon during nitrate withdrawal

Organic nitrates are first-line drugs in the therapy and prevention of angina. These compounds, are acutely effective yet some formulations demonstrate a rapid decline in effect with chronic use. In this review the mechanisms of development of nitrate tolerance and the different strategies to prevent it are considered. If frequent dosing, high dosages and long acting preparations giving constant 24 h plasma GTN levels are more likely to cause tolerance, nitrate-low periods seem to be effective in restoring the drug's efficacy. Intermittent therapy with GTN patches, an effective way to prevent tolerance, raises the problem of the rebound phenomenon during the removal period. Considerable variations in its occurrence have been reported and in this review the factors that may influence the incidence of the rebound are discussed. The dangers of rebound can be lessened by concomitant anti-anginal drugs or avoiding any abrupt decline in blood nitrate concentrations. The use of beta-blockers or calcium channel blockers during intermittent therapy with GTN patches and oral preparations of isosorbide dinitrate or isosorbide 5-mononitrate seem to be effective for this purpose.

Efficacy of intermittent (eight hours off) transdermal nitrate therapy in stable angina

The efficacy of intermittent (16 h on/8 h off) transdermal nitrate therapy (0.4 mg/h) was assessed in 46 patients with chronic stable angina, all but one of whom were on concomitant beta-blocker and/or calcium antagonist therapy. The study was a randomised, double-blind placebo-controlled crossover with two consecutive 7-day treatment periods, conducted at two centres. Prior to entry into the study patients were screened for exercise test reproducibility and nitrate response. Patch efficacy was determined by maximal symptom limited treadmill stress testing (Bruce protocol) and subjective diary card data. Analysis of variance showed that active treatment significantly improved time to onset of angina (P < 0.001), time to 1 mm ST-segment depression (P < 0.001) and total exercise duration (P < 0.001) compared with placebo from 385.7, 310.8 and 458.1 s to 455.7, 385.2 and 497.1 s, respectively. Nitrate patch therapy significantly reduced diastolic and systolic blood pressures without significantly increasing resting heart rate. There was a marginal reduction in the incidence of angina attacks and sublingual nitroglycerine consumption during active treatment. We conclude that intermittent transdermal nitrate therapy significantly improves exercise tolerance in patients with chronic angina pectoris and that this improvement occurs in addition to conventional anti-anginal therapy.

Pharmacokinetic characterisation of transdermal delivery systems

The key aspects of the pharmacokinetics of transdermal delivery systems including time lag, steady-state plasma levels and decline phase are illustrated in this review. The 7 currently marketed transdermal systems [nitroglycerin (glyceryl trinitrate), estradiol, clonidine, fentanyl, nicotine, scopolamine (hyoscine) and estradiol/norethisterone acetate] are discussed, as are systems in development. Single-dose absolute bioavailability studies characterise the period of onset, the steady-state plateau and the declining phase, and typify transdermal delivery. More complex temporal profiles result from interactions with enhancers or removal of the system before steady-state conditions are achieved. Clinically these systems are used to achieve multiple peak serum estradiol concentrations after application of transdermal estradiol, and an initial peak systemic concentration of testosterone after application of transdermal testosterone. Multiple-dose, dose proportionality and skin site bioequivalence studies are needed for the full pharmacokinetic characterisation of a transdermal delivery system. The relationship of system design to variability is discussed. Although the data are limited, population factors, cutaneous metabolism and tolerance all appear to influence the disposition of drugs administered transdermally. For example, the route of delivery influences which nitroglycerin metabolite predominates. Furthermore, as a result of tolerance to nitrates, a transdermal delivery system must be removed for 8 to 12 hours for optimal effect. Therefore, transdermal delivery systems, designed on the basis of pharmacokinetic principles and concentration-effect relationships, have the potential to provide optimal therapy for the treatment of some conditions.

Silent myocardial ischemia

The documentation of abnormalities related to myocardial ischemia, whether symptomatic or silent, is of central importance. Whenever this information is available, it should be used in the overall assessment of the patient at risk for adverse outcome. The level of concern for treatment of CAD should be based on the risk implications associated with the ischemia-related abnormalities detected during objective testing rather than on the presence or absence of pain. The exercise stress test is still the single most useful test to begin the evaluation of a patient with an analyzable ST segment. In persons suspected of having CAD, the detection of ischemic-type ST-segment depression, at a low workload (e.g., < 120 beats/min or < 6.5 METS) of > 2 mm magnitude or persisting for more than 6 min implies high risk for adverse outcome. Asymptomatic ischemia during everyday activities, detected by Holter monitoring, in the high-risk patient, most probably adds additional risk beyond the risk of an abnormal stress test alone. Left ventricular imaging by two-dimensional echocardiography, RNA, angiogram, vest, etc, showing an ejection fraction > or = 40%, reversible wall motion abnormalities in multiple regions and redistribution defects or a failure to increase ejection fraction during exercise even if the patient remains asymptomatic, also imply high risk. The presence of any of these abnormal findings, regardless of symptoms, should therefore prompt as high a degree of concern as with ischemia-related signals associated with pain. Thus any therapy chosen should be directed toward elimination of transient ischemia, not just relief of symptoms that may or may not be ischemia related. If this course is chosen, the efficacy of the therapeutic regimen and possible progression of CAD should be assessed with follow-up testing for ischemia. We believe that risk factor modification and aspirin should be considered for most, if not all, patients in whom ischemia, silent or symptomatic, is suspected or detected. If symptoms or ischemia suggesting low risk is present, anti-ischemic medical therapy may be considered, but follow-up is advised. If a high-risk ischemic signal, even without symptoms, is detected, medical therapy should be used to attempt to modify the signal. If the ischemic signal suggesting high risk persists despite medical therapy, revascularization should be considered. Until additional data from large clinical trials are available, this approach appears to have the greatest likelihood of modifying the adverse outcome of CAD.

Lack of rebound during intermittent transdermal treatment with glyceryl trinitrate in patients with stable angina on background beta blocker

OBJECTIVE

To assess whether intermittent transdermal treatment with glyceryl trinitrate causes clinically significant rebound in patients maintained on beta blockers for stable angina pectoris.

DESIGN

Serial treadmill exercise testing in a double blind, randomised, placebo controlled cross over trial. Baseline exercise testing was performed at 0900 and 1100 at visit 1. Transdermal glyceryl trinitrate patches releasing 15 mg/24 h were applied at 2200 the evening before visits 2 and 3, and exercise testing was performed at 0900 the next morning. The patch was removed and replaced with either an identical patch or matching placebo and exercise tests were repeated two hours later. The alternative treatment was given at visit 3.

SETTING

Tertiary referral centre.

PATIENTS

14 patients with stable angina pectoris maintained on beta blocker treatment alone.

MAIN OUTCOME MEASURES

Time to angina, 1 mm ST segment depression, and total time, together with heart rate, systolic blood pressure, and rate-pressure product.

RESULTS

Active treatment improved treadmill performance at 0900 and 1100. Time to angina, time to 1 mm ST segment depression, and total time fell significantly on placebo compared with the 0900 exercise test on active treatment, but were not significantly different to the baseline exercise test either.

CONCLUSIONS

Intermittent transdermal treatment with glyceryl trinitrate is not associated with the rebound phenomenon in patients maintained on beta blockers for stable angina pectoris.

Transdermal nitroglycerin reduces the frequency of anginal attacks but fails to prevent silent ischemia

OBJECTIVES

The aim of this study was to objectively evaluate the effects of intermittent administration of transdermal nitroglycerin on effort tolerance, frequency of anginal attacks and presence of silent ischemic events that occur during normal daily activities.

BACKGROUND

Previous studies have shown that transdermal nitroglycerin patches reduce the incidence of anginal attacks and improve exercise capacity when given intermittently. However, no carefully controlled studies are available on the effects of these preparations (and their dosing schedule) on the occurrence of "silent" ischemic events during unrestricted daily activities.

METHODS

Twelve men with chronic stable angina, a positive exercise test result and significant coronary artery disease completed a randomized, double-blind, placebo-controlled trial in which patches were worn either continuously or with overnight (8 h) removal. The effects of treatment were objectively assessed by both treadmill exercise testing and 24-h ambulatory electrocardiographic monitoring.

RESULTS

Only the intermittent dosing schedule afforded a small but significant improvement in exercise tolerance and prolonged exercise duration and time to ST segment depression. The frequency of anginal attacks was also reduced by both the continuous and intermittent treatment, but the effects on symptoms were not paralleled by a concomitant reduction in ischemic episodes recorded during ambulatory monitoring.

CONCLUSIONS

The results indicate that when used as monotherapy, intermittent transdermal nitroglycerin preparations lessen symptoms but are ineffective for the long-term prophylaxis of silent myocardial ischemia.

Role of nitrates in angina pectoris

Nitrates are used extensively for the treatment of angina pectoris. However, continuous therapy with either oral nitrates or nitroglycerin patches leads to rapid development of tolerance, with loss or diminution of antianginal and anti-ischemic effects. The only practical way to avoid the development of tolerance is to use intermittent daily therapy with nitrates. Nitroglycerin patches applied for 10-12 hours during the day increase exercise duration for 8-12 hours, but a rebound increase in anginal attacks during the nitrate-free interval may occur. Oral isosorbide-5-mononitrate, 20 mg twice a day, with the first dose administered in the morning and the second dose 7 hours later, increases exercise duration for at least 12 hours without the development of tolerance to either the morning or afternoon dose. This dosing regimen has been shown not to produce a rebound phenomenon during the periods of low nitrate levels at night and early hours of the morning. Isosorbide dinitrate (30 mg) prescribed at 7 AM and 1 PM does not produce tolerance to the 7 AM dose, but effects of the afternoon dose have not been evaluated. Recent data suggest that isosorbide dinitrate given 3 or 4 times daily produces tolerance and this dosing schedule is inadequate for antianginal prophylaxis. It should be recognized that intermittent oral or patch therapy with nitrates during the day leaves the patient unprotected at night and early hours of the morning. If this is of concern, additional therapy with another class of antianginal agent, preferably a long-acting beta blocker or a long-acting calcium antagonist should be instituted.

Daily life ischemia and nitrate therapy

Daily life ischemia has generated considerable interest because most of it is silent and associated with increased risk of adverse outcome. Coronary vasomotion, as well as increases in myocardial oxygen demand, seem important in the pathogenesis of this form of ischemia, so treatment with nitrates seems rational. Administration of sublingual nitroglycerin hourly, over 12 hours, was shown to decrease both silent and painful ischemic episodes in patients with effort angina. Subsequently, isosorbide dinitrate or mononitrate, given either as an intravenous infusion or orally, was shown to decrease both silent and painful ischemic episodes in patients with unstable rest angina and in those with severe angina. More recently, 6 studies have reported using transdermal nitroglycerin for daily life ischemia. Three of these reported open-label uncontrolled observations and suggested that ischemia frequency may be reduced approximately 60-80% during treatment with doses of 10-30 mg/day, with a duration of treatment ranging from 1 hour to 14 days. In 2 of these reports the duration of ischemia also decreased. The other 3 studies were randomized, double-blind, placebo-controlled studies with a total enrollment of 86 patients. These studies provided mixed results. One suggested that evidence for partial tolerance develops within 1 day of treatment, using large continuous or intermittent doses (mean, 52 mg/day). Another suggested that no tolerance develops to intermittent dosing (18 mg/16 hr out of 24 hr) during exercise testing but no effect is seen on daily life ischemia. The remaining study suggested that tolerance does not develop using small doses (15 mg/day) continuously over 14 days for ischemia during daily life, and that this response is different from that observed using the calcium antagonist nifedipine. These limited observations and conflicting results underscore a need for additional larger controlled trials, employing topical nitrate therapy in low intermittent doses for daily life ischemia.

Circadian patterns of myocardial ischaemia and the effects of antianginal drugs

Chronopathology of cardiovascular disease is now well documented. Silent myocardial ischaemia involves the same pathophysiological changes as conventional ischaemia. Early morning peaks in angina and myocardial ischaemia call for adequate timing of medication. beta-blockers abolish the morning peak, and aspirin reduces morning infarctions. The effects of other antianginals on these phenomena are presently unknown.