Efficacy of mibefradil compared with amlodipine in suppressing exercise-induced and daily silent ischemia: results of a multicenter, placebo-controlled trial

Stable angina pectoris: the medical management of symptomatic myocardial ischemia

Coronary artery disease (CAD) remains an important cause of morbidity and mortality and is a serious public health problem. Over the last 4 decades there have been dramatic advances in the both the prevention and treatment of CAD. The management of CAD was revolutionized by the development of effective surgical and percutaneous revascularization techniques. In this review we discuss the importance of the medical management of symptomatic, stable angina. Medical management approaches to both the treatment and prevention of symptomatic myocardial ischemia are summarized. In Canada, organic nitrates, β-adrenergic blocking agents, and calcium channel antagonists have been available for the therapy of angina for more than 25 years. All 3 classes are of proven benefit in the improvement of symptoms and exercise capacity in patients with stable angina. Although there is no clear first choice within these classes of anti-anginal agents, the presence of prior or concurrent conditions (for example, prior myocardial infarction and/or hypertension) plays an important role in the choice of anti-anginal class in individual patients. For some patients, combinations of different anti-anginal agents can be effective; however it is recommended that this approach be individualized. Although not currently available in Canada, other classes of anti-anginal agents have been developed; their mechanism of action and clinical efficacy is discussed. Patients with stable angina have an excellent prognosis. Patients in this category who obtain relief from symptomatic myocardial ischemia may do well without invasive intervention.

Development of newer calcium channel antagonists: therapeutic potential of efonidipine in preventing electrical remodelling during atrial fibrillation

Calcium channel antagonists are most frequently prescribed for the treatment of hypertension and the majority specifically inhibit the L-type Ca2+ channel. In order to prevent reflex sympathetic over activity caused by L-type calcium channel antagonists (calcium channel blockers [CCBs]), increasing attention has focused on the blockade of the T-type Ca2+ channel. The T-type Ca2+ channel is found in the kidney and can also appear in the ventricle of the heart when in failure. Therefore, the T-type Ca2+ channel is a possible new target for the treatment of nephropathy and heart failure. In clinical trials, the efficacy and safety of T-type CCBs in hypertension and chronic renal disease have been reported. It is well known that the T-type Ca2+ channel is present in the adult atrium and plays a role in the cardiac pacemaker, but recent experimental studies suggest that this current also promotes electrical remodelling of the atrium. Using efonidipine, a dual L- and T-type CCB, it has been demonstrated that atrial electrical remodelling can be diminished in dogs. Furthermore, the T-type Ca2+ channel has recently been found in the pulmonary veins, contributing to the pulmonary vein pacemaker activity and triggered activity. A variety of drugs having T-type CCB effects have been shown to be effective in the management of atrial fibrillation, suggesting that this channel may be a novel therapeutic target.

Additional antianginal and anti-ischemic efficacy of mibefradil in patients concomitantly treated with long-acting nitrates for chronic stable angina pectoris

BACKGROUND

Mibefradil, a newly approved antihypertensive and antianginal drug, is the first member of a new class of calcium antagonists (CAs), the tetralol derivatives, that selectively blocks T-type Ca2+ channels in contrast to classical CAs which, at therapeutic concentrations, block only L-type Ca2+ channels. Since patients with chronic stable angina pectoris typically may be treated with the combination of a long-acting nitrate and a CA, the additive efficacy and safety of mibefradil in combination with nitrate therapy needs to be determined.

HYPOTHESIS

This study was designed to assess the efficacy, tolerability, and safety of mibefradil when added to long-acting nitrate therapy in patients with chronic stable angina pectoris.

METHODS

Following a 1-week placebo run-in period, patients were randomized to receive either mibefradil 50 mg (n = 96) or placebo (n = 93) once daily in addition to their nitrate therapy. After 2 weeks of active treatment, patients receiving the mibefradil were force titrated to 150 mg once daily for an additional 2 weeks. Exercise tolerance tests (ETTs) were performed at the end of Weeks 2 and 4; patients also maintained an anginal diary during the 4-week treatment period.

RESULTS

After 2 weeks of treatment with 50 mg mibefradil (within the current recommended dose range), a statistically significant but modest increase in total exercise duration was observed (treatment effect 16.4 s, p = 0.04). Similarly, there was a significant increase in time to onset of ischemia (treatment effect 26 s, p = 0.008). The adverse event profile of the 50 mg dose was indistinguishable from placebo, indicating that this dose was extremely well tolerated. At Week 4, the mibefradil-treated patients were taking 150 mg, which is above the current recommended dose range. The increase in total exercise duration was larger for the mibefradil 150 mg group than for the placebo group. For the intent-to-treat population, this difference did not reach statistical significance, whereas in the standard population it did (treatment effect 21 s, p = 0.05). The other two ETT variables, time to onset of angina and time to onset of 1 mm ST-segment depression, demonstrated significantly greater effect with mibefradil 150 mg (treatment effects 40 s, p = 0.002, and 55 s, p < 0.001, respectively, for the intent-to-treat population). Mibefradil 150 mg was associated with more adverse events than placebo, specifically, dizziness, leg edema, and postural hypotension.

CONCLUSIONS

This study demonstrates that mibefradil 50 mg once daily in the setting of the background long-acting nitrate therapy produces additive antianginal and anti-ischemic effects and is extremely well tolerated.

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.

Defining the role of calcium channel antagonists in heart failure due to systolic dysfunction

Calcium channel antagonists (CCAs) may either be divided into the dihydropyridines (e.g. amlodipine, felodipine, isradipine, lacidipine, nilvadipine, nifedipine, nicardipine etc.), the phenylalkylamines (e.g. verapamil) and the benzothiazepines (e.g. diltiazem) according to their chemical structure, or into first generation agents (nifedipine, verapamil and diltiazem) and second generation agents (subsequently developed dihydropyridine-derivatives). Second generation CCAs are characterized by greater selectivity for calcium channels in vascular smooth muscle cells than the myocardium, a longer duration of action and a small trough-to-peak variation in plasma concentrations. Heart failure is characterized by decreased cardiac output resulting in inadequate oxygen delivery to peripheral tissues. Although the accompanying neurohormonal activation, leading to vasoconstriction and increased blood pressure, is initially beneficial in increasing tissue perfusion, prolonged activation is detrimental because it increases afterload and further reduces cardiac output. At the level of the myocyte, heart failure is associated with increased intracellular calcium levels which are thought to impair diastolic function. These changes indicate that the CCAs would be beneficial in patients with heart failure. There has been a strong interest and increasing experience in the use of CCAs in patients with heart failure. Despite potential beneficial effects in initial small trials, findings from larger trials suggest that CCA may have detrimental effects upon survival and cardiovascular events. However, this may not necessarily be a 'class b' effect of the CCAs as there is considerable heterogeneity in the chemical structure of individual agents. Clinical experience with different CCAs in patients with heart failure includes trials that evaluated their effects on hemodynamic parameters, exercise tolerance and on symptomatology. However, the most relevant results are those from randomized clinical trials that assessed mortality as the primary endpoint. First generation CCAs have direct negative inotropic effects and even sustained release formulations have not proved any beneficial effect upon survival. With second generation CCAs, some benefit on hemodynamic parameters has been observed but none on survival, alone or in combination with ACE inhibitors. It is noteworthy that although amlodipine had a neutral effect on morbidity and mortality in large, randomized, placebo-controlled trials in patients with heart failure, the drug was well tolerated. There is no specific indication for CCAs (first or second generation) in patients with systolic heart failure, alone or in combination with ACE inhibitors, but amlodipine may be a considered in the management of hypertension or coronary artery disease in patients with heart failure.

Silent myocardial ischemia: concepts and controversies

Silent myocardial ischemia is a relatively common, but poorly understood, clinical entity. The most accurate means of detecting silent myocardial ischemia and the precise treatment endpoints remain unclear. However, the amount of ischemic myocardium appears to correlate with the likelihood of future adverse cardiac events. Evidence suggests that patients at highest risk of severe myocardial ischemia, even in the absence of symptoms, derive the greatest benefit from an aggressive diagnostic and therapeutic approach. This paper reviews the diagnosis and treatment of silent myocardial ischemia, and its clinical implication in select patient groups: those without coronary artery disease, those with coronary artery disease, diabetic patients, postrevascularization patients, and women.

Clinical efficacy of efonidipine hydrochloride, a T-type calcium channel inhibitor, on sympathetic activities

Dihydropyridine Ca antagonists cause reflex tachycardia related to their hypotensive effects. Efonidipine hydrochloride has inhibitory effects on T-type Ca channels, even as it inhibits reflex tachycardia. In the present study, the influence of efonidipine hydrochloride on heart rate and autonomic nervous function was investigated. Using an electrocardiogram and a tonometric blood pressure measurement, autonomic nervous activity was evaluated using spectral analysis of heart rate/systolic blood pressure variability. Three protocols were used: (1) a single dose of efonidipine hydrochloride was administered orally to healthy subjects with resting heart rate values of 75 beats/min or more (high-HR group) and to healthy subjects with resting heart rate values less than 75 beats/min (low-HR group); (2) efonidipine hydrochloride was newly administered to untreated patients with essential hypertension, and autonomic nervous activity was investigated after a 4-week treatment period; and (3) patients with high heart rate values (>/=75 beats/min) who had been treated with a dihydropyridine L-type Ca channel inhibitor for 1 month or more were switched to efonidipine hydrochloride and any changes in autonomic nervous activity were investigated. In all protocols, administration of efonidipine hydrochloride decreased the heart rate in patients with a high heart rate, reduced sympathetic nervous activity, and enhanced parasympathetic nervous activity. In addition, myocardial scintigraphy with (123)I-metaiodobenzylguanidine showed significant improvement in the washout rate and H/M ratio of patients who were switched from other dihydropyridine Ca antagonists to efonidipine hydrochloride. Efonidipine hydrochloride inhibits increases in heart rate and has effects on the autonomic nervous system. It may be useful for treating hypertension and angina pectoris, and may also have a cardiac protective function.

Randomized comparison of T-type versus L-type calcium-channel blockade on exercise duration in stable angina: results of the Posicor Reduction of Ischemia During Exercise (PRIDE) trial

BACKGROUND

Mibefradil is a T-type calcium-channel antagonist and arterial vasodilator with negative chronotropic effects. It is not known if T-type calcium-channel blockade is superior to L-type calcium-channel blockade in patients with stable angina pectoris.

METHODS

A multicenter, randomized, double-blind trial was conducted in patients with documented coronary disease and stable angina to compare a 360 mg dose of diltiazem CD with 100 mg dose of mibefradil. The primary end point was change in time to symptom-limited exercise termination from baseline to 8 weeks. Secondary efficacy parameters included time to onset of persistent ST-segment depression, time to awareness of angina, and change in exercise duration from baseline to 2 and 4 weeks of treatment.

RESULTS

A total of 121 patients were randomized to mibefradil and 113 to diltiazem CD. At 8 weeks, the increase in exercise duration was 24.5 seconds greater in the mibefradil group (P =.017; 95% CI 4.4-44.7 seconds). At 8 weeks, time to development of > or =1 mm ST-segment depression was greater by 45.3 seconds (P =.0025; 95% CI 16.2-74.5) with mibefradil, but time to development of angina was not significantly different.

CONCLUSION

T-type calcium-channel antagonism with mibefradil improved treadmill exercise parameters compared with diltiazem in patients with chronic stable angina. Further investigation and development of antagonists of T-type calcium channels with fewer adverse drug interactions is warranted and may be promising in the management of ischemic heart disease.

Silent ischaemia and hypertension

For many years now, silent ischaemia has been recognized as a distinct clinical entity, and its relevance in different patient groups has been established. However, a number of basic questions have not been answered. In explaining the pathophysiology of silent ischaemia, factors affecting both the demand and the supply side are now being recognized. With the exception of certain well-defined groups, it is not clear why some patients are mostly symptomatic, while other patients are predominantly asymptomatic. There appear to be many factors influencing the ischaemic pain threshold. Studies investigating the prevalence of silent ischaemia show a remarkably high prevalence of silent ischaemia in different patient groups. Patients with hypertension but without coronary artery disease form a specific and vulnerable high-risk population that is particularly prone to silent ischaemia. Since changes at the macrovascular level are not responsible, various factors negatively influencing either cardiac supply or demand have been investigated. A reduced coronary reserve is central in explaining the increased prevalence of silent ischaemia in hypertensives. Left ventricular hypertrophy renders meaningful detection of ST segment changes difficult, but a possible solution dealing with this problem is offered by applying more stringent criteria in terms of minimal ST depression in the definition of ischaemia. The treatment of silent ischaemia is largely the same as for angina pectoris, but whether therapy should be directed at elimination of all ischaemic episodes or only of symptomatic episodes depends on further prospective work addressing this question.

Beneficial effects of the T- and L-type calcium channel antagonist, mibefradil, against exercise-induced myocardial stunning in dogs

Abnormalities in calcium homeostasis such as calcium overload have been shown to participate in the pathogenesis of myocardial stunning. The goal of this study was to investigate the effects of mibefradil, a mixed T- and L-type calcium channels antagonist on exercise-induced ischemia (i.e., high-flow ischemia). Nine dogs were permanently instrumented to measure left ventricular wall thickening (Wth) and coronary blood flow (Doppler). Infusion of saline or mibefradil (30 and 40 microg/kg/min, i.v., for 20 min) was started 10 min before exercise (10 min, 14 km/h; slope, 13%) and stopped at its end. Circumflex coronary artery stenosis (pneumatic occluders) was set up 5 min before exercise to suppress exercise-induced increase in mean coronary blood flow without simultaneously affecting Wth at rest. Mibefradil (30 microg/kg/min) was also administered at the beginning of the recovery period in a subset of four dogs. During exercise with saline, Wth was dramatically reduced (-77 +/- 7%; p < 0.05) and recovered only after 24 h. Mibefradil at both doses significantly limited tachycardia during exercise (211 +/- 7 and 210 +/- 5 beats/min vs. 240 +/- 8 beats/min for mibefradil, 30 microg/kg/min, mibefradil, 40 microg/kg/min, and saline, respectively) but exerted no negative inotropic effects. Mibefradil at both doses significantly reduced the intensity of myocardial stunning and the time to recovery in Wth (3 h). Administration of mibefradil at the beginning of the recovery period did not protect against myocardial stunning. Administration of a mixed T- and L-type calcium channel antagonists before ischemia confers cardioprotection against exercise-induced myocardial stunning. This may potentially be related to the limitation of exercise-induced tachycardia and/or the prevention of calcium overload.

Exercise-induced silent myocardial ischemia and future cardiac events in healthy, sedentary, middle-aged and older men

OBJECTIVES

Before men older than age 45 participate in vigorous exercise programs, the American Heart Association and the American College of Sports Medicine recommend they undergo a screening maximal exercise treadmill test. We examined the predictive value for subsequent cardiac events of exercise-induced silent myocardial ischemia (SI) during the exercise treadmill test in healthy, sedentary, obese, middle-aged and older men recruited for research studies.

DESIGN

A cohort study with 7 years of follow-up.

SETTING

Out-patient research at a tertiary hospital.

PARTICIPANTS

170 healthy, sedentary, obese, middle-aged and older (ages 45-79 years) men with no prior history of coronary artery disease (CAD) recruited for research studies.

MEASUREMENTS

Cardiac risk factors, exercise-induced SI (ST segment depression on the electrocardiogram during a maximal exercise treadmill test), maximal aerobic capacity (VO2max), and 7- year follow-up data on incident CAD.

RESULTS

At baseline, 37 of the men (22%) had exercise-induced SI on their treadmill tests. Seven-year follow-up data was obtained in 97% of the patients. In the interim, 31 men had cardiac endpoints (sudden cardiac death, myocardial infarction, angioplasty, coronary artery bypass graft surgery, angina), and four had noncardiac deaths. Seventeen of the 37 men (46%) with exercise-induced SI on their baseline exercise tests had cardiac endpoints compared with 14 of 133 (11%) men with normal exercise tests (P < .001). Compared with the men with no cardiac endpoints, the men with subsequent cardiac endpoints were older (63 +/- 1 vs 58 +/- 1 years, mean +/- SEM, P < .001) and had a lower maximal aerobic capacity (VO2max) (24 +/- 1 vs 29 +/- 1 mL/kg/min, P < .001). In Cox proportional hazards analysis, exercise-induced SI and a low VO2max were independent predictors of subsequent cardiac endpoints.

CONCLUSION

In a healthy population of obese, sedentary, middle-aged and older men, exercise-induced SI and low VO2max were predictors of incident CAD. This suggests that exercise treadmill testing is beneficial in assessing risk for future cardiac events in obese, sedentary individuals.

Treatment of stable angina

Severe atherosclerotic narrowing of one or more coronary arteries is responsible for myocardial ischemia and angina pectoris in most patients with stable angina pectoris. The coronary arteries of patients with stable angina also contain many nonobstructive plaques, which are prone to fissures or rupture resulting in presentation of acute coronary syndromes (unstable angina, myocardial infarction, sudden ischemic death). In addition to symptomatic relief of symptoms and an increase in angina-free walking time with antianginal drugs or revascularization procedures, the recent emphasis of treatment has been to reduce adverse clinical outcomes (coronary death and myocardial infarction). The role of smoking cessation, aspirin, treatment of elevated lipids, and treatment of high blood pressure in all patients and of beta-blockers and angiotensin-converting enzyme inhibitors in patients with diminished systolic left ventricular systolic function in reducing adverse outcomes has been well established. What is unknown, however, is whether any anti-anginal drugs (beta-blockers, long-acting nitrates, calcium channel blockers) effect adverse outcomes in patients with stable angina pectoris. Recent trials evaluated the usefulness of suppression of ambulatory ischemia in patients with stable angina pectoris, but it remains to be established whether suppression of ambulatory myocardial ischemia with antianginal agents or revascularization therapy is superior to pharmacologic therapy targeting symptom relief. Patients who have refractory angina despite optimal medical treatment and are not candidates for revascularization procedures may be candidates for newer techniques of transmyocardial revascularization, enhanced external counterpulsation, spinal cord stimulation, or sympathectomy. The usefulness of these techniques, however, needs to be confirmed in large randomized clinical trials.

Anti-ischemic effects of amlodipine in patients with stable angina pectoris and myocardial ischemia during daily life. Amlodipine Study Group

Ambulatory electrocardiographic monitoring was used to assess the anti-ischemic effects of amlodipine in a subset of 56 patients enrolled in a 14-week withdrawal study; amlodipine therapy resulted in a marked decrease in the overall mean number of ischemic events and the average number of transient ischemic episodes (p <0.005). Amlodipine substantially reduced the number of ischemic events among all patients during the single-blind phase, with further significant reductions recorded among patients who remained on amlodipine during double-blind therapy, but the number of ischemic events increased almost to baseline levels in patients switched to placebo during double-blind therapy (p = 0.01 by analysis of variance).

The relevance of T-type calcium antagonists: a profile of mibefradil

L- and T-type voltage-dependent transmembrane calcium channels are important for normal functioning of the cardiovascular system. T-type channels are a heterogeneous group, and have physiologic and pathophysiologic relevance in a number of organ systems, including the heart and central nervous system. They appear to be involved in the control of blood pressure in patients with essential hypertension and in protection from ischemic damage. Alterations of both L- and T-type calcium channels are involved in the development of hypertension. Pharmacologic modulation of T-type calcium channels appears to reduce membrane calcium flux and ameliorate hypertension. During early ischemic damage, T-type calcium channels appear to remain functional whereas L-type channels are already inactivated. T-type calcium channels also appear to be involved in the development of supraventricular arrhythmias, some forms of arrhythmias in cardiomyopathy, and cardiac hypertrophy. The heterogeneity of T-type calcium channels should make it possible to target drugs to specific subgroups of T-type calcium channels. A new class of calcium antagonist, the benzimidazolyl-substituted tetraline derivatives, has been shown to block both L- and T-type calcium channels. The first member of this class approved for clinical use is mibefradil. Clinical studies have demonstrated the efficacy of mibefradil in lowering blood pressure and as an antianginal and antiischemic agent. At clinically recommended doses, mibefradil has a heart rate lowering effect without a negative inotropic effect, and a favorable side effect profile. Because it is metabolized by the cytochrome P450 pathway, it should be used cautiously with other agents similarly metabolized.

Mibefradil: a new class of calcium-channel antagonists

OBJECTIVE

To describe the pharmacology, pharmacokinetics, and clinical efficacy of mibefradil compared with other agents used for hypertension and angina.

DATA SOURCES

A MEDLINE search was performed for the period of January 1980 through September 1997 using the key terms mibefradil or Ro 40-5967. All articles written in English were considered for review.

STUDY SELECTION AND DATA EXTRACTION

All clinical studies involving mibefradil were evaluated. Preclinical data were included if these data were not adequately represented in clinical (human) studies.

DATA SYNTHESIS

Mibefradil is the first member of a new class of calcium-channel antagonists (CCAs) that block the T-type calcium channels. A long elimination half-life makes once-daily dosing feasible, and the drug's lack of negative inotropy and reflex tachycardia distinguishes it from other available CCAs. When administered at recommended dosages (50 or 100 mg once daily), mibefradil reduces blood pressure over 24 hours in patients with hypertension, improves exercise capacity, and relieves anginal symptoms in patients with chronic stable angina pectoris.

CONCLUSIONS

Clinical studies have found that the antihypertensive effects of mibefradil are comparable with those of nifedipine, verapamil, and amlodipine, and more effective than those of diltiazem. These effects result from peripheral vasodilation and a slight reduction in heart rate. Selective vasodilation of the coronary vasculature makes it an effective antianginal agent when used alone or added to beta-blocker therapy. Mibefradil demonstrates no significant effects on cardiac contractility, and no adrenergic stimulation resulting in reflex tachycardia. Therefore, it may have some advantages over currently available CCAs, especially in patients with congestive heart failure, although such advantages are unproven in published clinical trials. Ongoing clinical studies, including the Mortality Assessment in Congestive Heart Failure Trial (MACH-1) currently in progress, are needed to clarify mibefradil's place in cardiovascular therapy.

Mibefradil: a selective T-type calcium antagonist

Mibefradil is the first of a new class of calcium antagonists with a unique structure and pharmacology. Its novel mechanism of action is characterized by L-type and selective T-type calcium channel blockade. Mibefradil is selective for smooth muscle over cardiac muscle and selectively dilates the coronary vasculature over the peripheral vasculature. In animal studies, mibefradil increases coronary blood flow during induced ischemia. In addition, in vitro studies demonstrated that mibefradil decreases smooth muscle proliferation in response to vascular injury. The most intriguing effects of mibefradil include a lack of negative inotropy and reflex tachycardia, as well as inhibition of pathologic hypertrophy and remodeling in response to vascular injury. In clinical trials, mibefradil (100 mg) was more effective than diltiazem dual-release capsules (360 mg) and as effective as amlodipine (10 mg) in treating mild-to-moderate hypertension; mibefradil (100 mg) also resulted in a greater reduction in sitting diastolic blood pressure than did nifedipine GITS (60 mg) in patients with moderate-to-severe hypertension. In patients with chronic stable angina, mibefradil (100 mg) was as effective as diltiazem SR capsules (120 mg) twice daily and more effective than amlodipine (10 mg) in improving exercise tolerance and reducing ischemic episodes. Mibefradil improved survival in a rat model of heart failure as effectively as the angiotensin-converting enzyme (ACE) inhibitor, cilazapril. The apparent lack of negative inotropic activity and neurohormonal activity with mibefradil, as well as its favorable effects on cardiac remodeling in experimental models, suggest that this agent may be beneficial in congestive heart failure. This hypothesis is being tested in the ongoing Mortality Assessment in Congestive Heart Failure (MACH-1) trial.

Mibefradil: A New Selective T-Channel Calcium Antagonist for Hypertension and Angina Pectoris

Calcium antagonists are an established therapy for patients with hypertension and angina pectoris, but their current usage is often limited by their pharmacologic profilers and side effects. Mibefradil is a recently developed calcium antagonist with a unique chemical structure, site of action, and set of pharmacologic effects. Unlike currently available calcium channels as well as L-type channels. It is further distinguished from the other calcium antagonists in that it is the first member of a new class of calcium antagonists, the tetralol derivatives. With chronic oral dosing, mibefradil attains steady-state plasma concentrations within 3-4 days, has a bioavailability of approximately 90%, and a plasma half-life of 17-25 hours. It has a gradual onset of action and can be administered once daily without regard to food intake. It increases coronary blood flow and lowers peripheral vascular resistance. The vasodilatory effects of mibefradil are associated with a lack of inotropic effect on myocardium, lack of neurohormonal activation, and a reduction in heart rate. In clinical trials it has been demonstrated to be an effective agent in the treatment of patients with hypertension and angina pectoris, with a good safety and tolerability profile regardless of age, gender, or race.

Antianginal and anti-ischemic effects of mibefradil in the treatment of patients with chronic stable angina pectoris

Five placebo-controlled, double-blind, multicenter, parallel-design studies were performed to evaluate the antianginal and anti-ischemic characteristics of the novel T-channel-selective calcium antagonist, mibefradil, in the treatment of patients with chronic stable angina pectoris. Of the 5 studies, 2 were monotherapy dose-finding trials and 3 were conducted in patients receiving background antianginal therapy: either beta blockers (2 studies) or long-acting nitrates (1 study). A total of 865 patients were randomized to 1 of 4 mibefradil dose groups (25, 50, 100, and 150 mg; n = 565) and placebo (n = 300). The antianginal and anti-ischemic effects of mibefradil were assessed across all 5 studies by evaluating exercise tolerance test variables, weekly number of anginal attacks and short-acting nitroglycerin consumption, and in both dose-finding studies, the number and total duration of silent ischemic episodes (48-hour Holter monitoring). A statistically significant increase in exercise duration was achieved in 3 of 5 studies with the 50-mg dose of mibefradil and in 3 of 3 studies with the 100-mg dose of the compound over the effects observed in the placebo groups. A significant delay in time to onset of ischemia during exercise was induced in all studies with the 50- and 100-mg doses of mibefradil. The 25-mg dose of mibefradil was not significantly better than placebo, and the effects of the 150-mg dose of the compound were similar to those observed with the 100-mg dose. Across all studies, a dose-related decrease was observed in the number of weekly anginal attacks and in weekly nitroglycerin consumption. Similarly, a significant dose-related decrease in the number and duration of silent ischemic episodes was observed during Holter monitoring for 48 hours in the 2 dose-finding studies. The antianginal and anti-ischemic effects were associated with a dose-related decrease in heart rate and double product both at rest and at exercise termination. Treatment with the 50- and 100-mg doses of mibefradil was found to be well tolerated and safe compared with placebo, a finding that held true for patients on chronic beta-blocker or long-acting nitrate therapy. Taken together, these studies indicate that mibefradil is an effective and well-tolerated once-daily treatment for chronic stable angina pectoris at doses of 50 and 100 mg, which are the lowest and highest effective doses of the compound, respectively.

Mibefradil in the treatment of chronic stable angina pectoris: comparative studies with other calcium antagonists

The ability of mibefradil, a new T-channel-selective calcium antagonist, to improve exercise tolerance and silent ischemic parameters in patients with chronic stable angina was compared in 3 separate trials with 2 other commonly used calcium antagonists: diltiazem SR (120 mg/twice daily) and amlodipine (10 mg/day). Compared with amlodipine, mibefradil 100 mg given once daily over a 3-week period resulted in a statistically significantly larger increase from baseline in total exercise tolerance test (ETT) duration (treatment difference of 40.9 sec, p = 0.04), time to onset of angina (treatment difference 61.2 sec, p < 0.001), and time to onset of ischemia (treatment difference of 54.4 sec, p = 0.004). The decrease in weekly anginal episodes was 58% with mibefradil versus 19% with amlodipine, and the reduction in nitroglycerin consumption was 58% with mibefradil versus a 10% increase with amlodipine. The decrease in the number of silent ischemic episodes detected by a 48-hour Holter recording was significantly larger (p = 0.03) with mibefradil 100 mg (88%) compared with amlodipine 10 mg (38%). Similarly, a larger decrease in the duration of silent ischemia was observed with mibefradil (69%) compared with that seen with amlodipine (38%). The preliminary results of a second trial comparing mibefradil with amlodipine were consistent with the first demonstrating that the improvement for all 3 ETT parameters was larger for mibefradil (ETT duration: 55.2 sec; delay in onset angina: 74.2 sec; time to onset of ischemia: 63.6 sec), but in this trial the treatment differences did not reach statistical significance. In the trial comparing mibefradil (100 mg once daily) with diltiazem SR (120 mg twice daily), both compounds had equivalent effects on all ETT parameters tested. Mibefradil produced a 21% increase in exercise duration compared with a 20% increase with diltiazem. Although mibefradil yielded larger increases in the time to onset of angina and the time to onset of 1-mm ST-segment depression (42% and 38%, respectively) than did diltiazem (34% and 25%, respectively), the treatment differences did not reach statistical significance. Both mibefradil and diltiazem SR were associated with at least a 70% reduction from baseline in anginal frequency and nitroglycerin consumption. Mibefradil-treated patients showed greater decreases in heart rate and the rate-pressure product at each stage of the ETT than patients treated with amlodipine or diltiazem SR. All 3 drugs were well tolerated. However, compared with mibefradil, amlodipine and diltiazem SR produced a higher incidence of leg edema. In conclusion, the effectiveness of mibefradil in improving all 3 ETT parameters was greater than that of amlodipine and equivalent to that of diltiazem SR. Moreover, mibefradil provided greater reductions in the heart rate and cardiac workload than did the other 2 drugs.