Haemodynamic advantages of combined alpha-blockade and beta-blockade over beta-blockade alone in patients with coronary heart disease

Labetalol (Trandate, Glaxo Inc.; Normodyne, Schering Corp.)

Labetalol is a competitive antagonist of α1-, β1-, and β2-adrenergic receptors. The hemodynamic effects of the drug include reduced blood pressure, heart rate, and peripheral resistance, with little change in resting cardiac output or stroke volume. In open trials and controlled studies, labetalol was an effective antihypertensive. Labetalol compared favorably with β-blockers alone or in combination with vasodilators, for the treatment of hypertension. Reductions in heart rate are less pronounced with labetalol as compared with propranolol. Labetalol produces rapid reductions in blood pressure when administered intravenously for severe hypertension. The most frequent adverse reactions to the drug include fatigue, postural symptoms, headache, and gastrointestinal complaints. Labetalol may prove advantageous when vasodilation in addition to β-blockade is desired, or for selected patients experiencing adverse effects attributable to β-blockade. Until the clinical profile of labetalol is better defined, the use of the drug should be limited.

β-Blockers, Cocaine, and the Unopposed α-Stimulation Phenomenon

Cocaine abuse remains a significant worldwide health problem. Patients with cardiovascular toxicity from cocaine abuse frequently present to the emergency department for treatment. These patients may be tachycardic, hypertensive, agitated, and have chest pain. Several pharmacological options exist for treatment of cocaine-induced cardiovascular toxicity. For the past 3 decades, the phenomenon of unopposed α-stimulation after β-blocker use in cocaine-positive patients has been cited as an absolute contraindication, despite limited and inconsistent clinical evidence. In this review, the authors of the original studies, case reports, and systematic review in which unopposed α-stimulation was believed to be a factor investigate the pathophysiology, pharmacology, and published evidence behind the unopposed α-stimulation phenomenon. We also investigate other potential explanations for unopposed α-stimulation, including the unique and deleterious pharmacologic properties of cocaine in the absence of β-blockers. The safety and efficacy of the mixed β-/α-blockers labetalol and carvedilol are also discussed in relation to unopposed α-stimulation.

Differential hemodynamic effects of beta-adrenoceptor blockers, Ca antagonists and combined alpha-beta-receptor blockade in ischemic heart disease

The hemodynamic responses to 3 different therapeutical regimens: beta-adrenoceptor blockade, calcium inflow inhibition and combined alpha-beta-blockade were evaluated in 3 matched randomized groups of patients with ischemic heart disease and typical exercise-induced angina. The groups consisted of 22, 16 and 15 men, mean age 55-59 years. They were studied at rest and during ischemia-inducing exercise, before and after single oral doses of 100 mg metoprolol, 10 mg nifedipine and 200 mg labetalol. Pressures in the brachial artery and the pulmonary circulation were recorded by means of percutaneously introduced catheters. Cardiac output was determined according to the Fick principle. Metoprolol reduced mean arterial pressures, heart rate and cardiac output. Systemic vascular resistance and left ventricular filling pressure increased. Nifedipine resulted under all conditions in a distinct reduction of systemic vascular resistance and arterial pressures and a slight increase in heart rate and cardiac output. Left ventricular filling pressure was significantly lowered, the more the higher the initial level. The effect of labetalol was similar to that of nifedipine; however, cardiac output was unchanged and heart rate was slightly reduced. Left ventricular filling pressure was significantly lower. It is apparent that suppression of adrenergic stimulation by beta-receptor blockade alone may have adverse hemodynamic effects in ischemic heart disease and prompt further functional deterioration. Conversely, both calcium and combined alpha-beta-receptor blockade tend to improve left ventricular function by lowering both left ventricular preload and total systemic vascular resistance. The results strongly suggest that in patients in whom beta-receptor blockers appear indicated, their adverse hemodynamic effects can be offset by concomitant alpha1-receptor blockade or vasodilation without losing symptomatic efficacy. Combined alpha-beta-receptor blockade has the advantage over calcium antagonists alone to prevent any increase in adrenergic activity and related hyperkinetic response.

Carvedilol: molecular and cellular basis for its multifaceted therapeutic potential

Carvedilol is a unique cardiovascular drug of multifaceted therapeutic potential. Its major molecular targets recognized to date are membrane adrenoceptors (beta 1, beta 2, and alpha 1), reactive oxygen species, and ion channels (K+ and Ca2+). Carvedilol provides prominent hemodynamic benefits mainly through a balanced adrenoceptor blockade, which causes a reduction in cardiac work in association with peripheral vasodilation. This drug assures remarkable cardiovascular protection through its antiproliferative/atherogenic, antiischemic, antihypertrophic, and antiarrhythmic actions. These actions are a consequence of its potent antioxidant effects, amelioration of glucose/lipid metabolism, modulation of neurohumoral factors, and modulation of cardiac electrophysiologic properties. The usefulness of carvedilol in the treatment of hypertension, ischemic heart disease, and congestive heart failure is based on a combination of hemodynamic benefits and cardiovascular protection.

Comparison of the hemodynamic effects of metoprolol and carvedilol in hypertensive patients

Metoprolol and carvedilol are widely used in the treatment of hypertension, but no randomized comparison of their hemodynamic activity has been previously reported. Their comparative effects on heart rate, systemic blood pressure, and echocardiographically determined aortic and femoral artery blood flow were measured at rest and at 2 and 24 hours after the first dose of each drug, and again after 4 weeks of sustained monotherapy in 12 male and 12 female patients, aged 36-68 years with uncomplicated sustained hypertension according to a randomized single-blind protocol. Nine patients in each drug group achieved the target diastolic blood pressure of < 90 mmHg on the initial doses of each drug; this was achieved in the remainder following doubling of each dose. Neither drug occasioned withdrawal of any patient due to adverse reactions. Both drugs significantly reduced heart rate, although the reduction at 2 hours was significantly greater after metoprolol than after carvedilol. Both drugs reduced systolic pressure throughout the study; the reduction at 2 hours was significantly greater after carvedilol than after metoprolol. In contrast, the diastolic blood pressure was persistently reduced only by carvedilol. The cardiac output, determined as the aortic systolic blood flow, after carvedilol was not significantly different from pretreatment values throughout the study but was significantly reduced in the metoprolol-treated patients at each point of measurement. After metoprolol the systemic and femoral vascular resistances derived from conventional formulae were consistently and significantly increased over pretreatment values throughout the study and were significantly greater than in the carvedilol group at all measurement points. The hemodynamic differences between these two beta-blocking drugs may be explained by the additional vasodilator activity of carvedilol associated with its alpha 1-adrenoceptor blocking activity. The long-term clinical and prognostic implications of these pharmacodynamic differences between beta-adrenoceptor antagonists with and without additional vasodilator activity in the treatment of hypertensive patients remain to be determined.

Transesophageal echocardiographic assessment of left ventricular function in response to labetalol for control of postoperative hypertension

Although labetalol (LAB), the combination of an alpha- and beta-adrenergic blocking agent, is thought to be effective and safe for the control of postoperative hypertension, no study has focused on changes in left ventricular (LV) function when this drug was used to control postoperative hypertension. Therefore, this study determined the effects of LAB on hemodynamics and LV function assessed by 2D transesophageal echocardiography (TEE) in 17 patients undergoing abdominal aortic surgery who experienced a postoperative hypertensive episode. Postoperatively, patients were transferred while still intubated and under fentanyl sedation to the postanesthesia care unit where a TEE probe was inserted to provide a short-axis view of the LV. When their systolic blood pressure increased above 165 mmHg for more than 4 minutes, LAB was given in a dose of 0.75 mg/kg IV, over 2 minutes. If the blood pressure was not lowered to within 10% of the preoperative values, additional doses of LAB were given. Control of hypertension was obtained in all patients and was associated with a significant decrease in heart rate (90 +/- 19 to 70 + 13 bpm), cardiac index (4.52 +/- 1.65 to 3.36 +/- 1.55 L/min/m2), and mixed venous oxygen saturation (73 +/- 10 to 63 +/- 10%). With the lower blood pressure, end-diastolic area increased, indicating myocardial depression. In conclusion, LAB can be used to effectively control hypertension during the early postoperative period after abdominal aortic surgery. However, the reduction of blood pressure is achieved principally by the negative inotropic effect of LAB, which predominates over its vasodilator action.

Hemodynamic and adrenergic effects of combined alpha/beta-receptor blockade versus combined beta-receptor and slow channel calcium blockade in patients with ischemic heart disease

The effects of combined alpha/beta-adrenoceptor blockade and of beta-receptor/slow channel calcium blockade on systemic and pulmonary hemodynamics and on adrenergic activity were compared in 2 matched groups of men suffering from ischemic heart disease. They were studied at rest supine and during ischemia-inducing exercise in the seated posture using invasive percutaneous techniques. Fourteen patients received 200 mg labetalol as a single oral dosis, 15 metoprolol (100 mg) plus nifedipine (10 mg). Both regimens reduced pressures in the systemic and pulmonary circulation under all conditions. At rest, stroke volume and cardiac output slightly decreased after labetalol and increased after metoprolol/nifedipine. During exercise the changes induced by the two regimens were virtually identical: heart rates and vascular resistances were reduced, stroke volume increased, cardiac output was not significantly changed. Plasma renin activity was lowered by labetalol, unchanged by metoprolol/nifedipine. Plasma adrenaline increased after metoprolol/nifedipine only, noradrenaline with both regimens. Both combinations significantly lowered stroke work and the rate pressure product and had similar beneficial effects on the onset and the duration of angina. It is concluded that both combinations attenuate or offset the potential adverse hemodynamic effects of beta-receptor blockade alone without loss but rather enhancement of symptomatic efficacy.

Differences in haemodynamic response to beta-blocking drugs between stable coronary artery disease and acute myocardial infarction

Theoretically the increased sympathoadrenal activity following acute myocardial infarction might augment the haemodynamic impact of beta-adrenoceptor blockade. To evaluate this question 32 haemodynamic studies were performed to compare the effects of equivalent beta-blocking doses of propranolol (8 mg i.v.) and pindolol (0.8 mg i.v.) in patients with a recent acute myocardial infarction (A.M.I.) or stable coronary artery disease (and a presumptive low sympathetic state). In stable coronary artery disease there were clear differences between the haemodynamic impact of propranolol and pindolol. Propranolol decreased both heart rate (delta HR -7 beat/min) and cardiac index (delta CI -0.4 l/min/m2), with an increased pulmonary artery occluded pressure (delta PAOP +4 mmHg) and systemic vascular resistance index (delta SVRI +358 dyn X s X cm-5 m2). However an equivalent beta-blocking dose of pindolol increased PAOP (delta PAOP +3 mmHg) leaving other variables unchanged. These differential actions of propranolol and pindolol have previously been ascribed to the intrinsic sympathomimetic activity (I.S.A.) of pindolol maintaining cardiac pumping function in a low sympathetic state. In contrast following myocardial infarction, both drugs reduced cardiac index to a significantly greater extent compared with stable coronary artery disease (delta CI propranolol -0.81/min/m2; pindolol -0.4 l/min/m2; p less than 0.05); propranolol also reduced the systemic arterial blood pressure (delta systolic -10 mmHg; delta mean -5 mmHg; p less than 0.05). The haemodynamic relevance of the I.S.A. of pindolol appeared attenuated following A.M.I. These data are compatible with experimental evidence of sympathetic nervous activation following coronary occlusion; the resulting hyperadrenergic state appears to condition an augmented haemodynamic response to beta-blocking drugs irrespective of their ancillary pharmacological properties.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects on left ventricular performance of verapamil and metoprolol singly and together in exercise-induced angina pectoris

Concurrent therapy with the calcium channel blocker, verapamil, and the beta-blocking group of compounds is usually felt to be clinically contraindicated due to the former's potent dromotropic and negative inotropic actions. The basis of this assumption was examined in a rest and exercise hemodynamic study of the effects of verapamil and the cardioselective beta-blocking drug, metoprolol, in 22 patients with stable angina pectoris and angiographically confirmed coronary artery disease. In a randomized study, 11 patients were assessed following intravenous verapamil (16 mg) alone, 11 following intravenous metoprolol (10 mg) alone, and all 22 were assessed on combination therapy. The plasma levels achieved at the time of each hemodynamic assessment were in the therapeutic range. At rest, verapamil alone significantly lowered systemic arterial pressure and vascular resistance; metoprolol alone lowered heart rate and increased systemic vascular resistance without change in systemic arterial pressure. Combination therapy reduced systemic arterial pressure and heart rate without change in cardiac output and systemic vascular resistance. During upright bicycle exercise, the changes were directionally similar. Depression of cardiac function (i.e., reduced cardiac output at increased pulmonary artery occluded pressure) occurred following metoprolol but not following verapamil; the addition of verapamil did not accentuate the depression of function induced by metoprolol. These results suggested that in patients with stable coronary artery disease, without manifest conduction system abnormality, the cardiac depressant actions of verapamil were countered by its vasodilator properties.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of haemodynamic dose-response effects of beta- and alpha-beta-blockade in acute myocardial infarction

The comparative haemodynamic dose-response effects of beta- (propranolol) or alpha- plus beta-blockade (labetalol) were evaluated in a randomised between-group study of 16 patients with an uncomplicated acute myocardial infarction. In equivalent beta-blocking doses both drugs equally reduced myocardial stroke work index and presumably myocardial oxygen requirements. However, although propranolol reduced heart rate and cardiac output, these haemodynamic changes were accompanied by an augmentation of systemic vascular resistance. In contrast, labetalol reduced heart rate, cardiac output without change in systemic vascular resistance. Moreover, concomitant alpha- and beta-blockade with labetalol resulted in lesser depression of cardiac output at equivalent beta-blocking doses to propranolol. These results suggest that the addition of alpha to beta-blockade may attenuate some of the adverse reflex circulatory consequences of pure beta-blockade; the usefulness of this pharmacological approach to the manipulation of the circulation in the early post-infarction period merits further study.

Alpha- and beta-blockade in angina pectoris

Angina pectoris encompasses a clinically diverse group of syndromes in which the common factor is myocardial ischaemia resulting from an imbalance between oxygen requirement and delivery. Anginal pain is most frequently precipitated by exercise, but may occur without any apparent cause at rest. Fixed obstructions in the coronary vessels, often attended by thickening of the overlying coronary artery media, are the most frequent cause of ischaemic cardiac pain. The resulting myocardial fibrosis impairs efficient filling and emptying of the ventricles, further aggravating the functional embarrassment resulting from the reduced coronary blood flow. In stable coronary heart disease the increased energy demands during exercise are associated with the rapid development of a haemodynamic profile characteristic of acute left ventricular failure. This results in further substantial increases in pressure work, wall stress and oxygen consumption of the left ventricle. The reflex sympathoadrenal consequences of these primary haemodynamic changes lead to further mechanical and electrical embarrassment of the ischaemic heart. Increased stimulation of beta 1- and beta 2-receptors in the heart increases heart rate and contractility and thereby myocardial oxygen demand. Increased stimulation of alpha-receptors in the peripheral veins and arteries indirectly increases left ventricular oxygen demand still further by increasing preload and afterload, respectively. The reduced blood flow to the endocardium enhances its sensitivity to increased sympathoadrenal stimulation and facilitates initiation of arrhythmias. Blockade of all adrenergic activity, particularly in the myocardium, coronary arteries and peripheral blood vessels should, therefore, help alleviate the myocardial ischaemia. There is a rational argument for the use of alpha-blockade in coronary heart disease, particularly in conjunction with beta-blockade. Attenuation of the risk of coronary spasm and ventricular arrhythmias and reduction of pressure work and left ventricular afterload are amongst the potential attributes of alpha-blockade. Alone, however, their utility is severely limited by the risks of hypotension and reduction in coronary perfusion pressure and reflex oxygen-wasting tachycardia. Alone, alpha-adrenoceptor antagonists have no place in the treatment of angina pectoris. beta-Adrenoceptor blocking drugs competitively inhibit catecholamines at both cardiac and peripheral vascular beta-adrenergic receptors. Their main advantage is that they reduce many of the important determinants of myocardial oxygen consumption, particularly by reducing the heart rate during exercise.(ABSTRACT TRUNCATED AT 400 WORDS)

Multicenter clinical evaluation of long-term efficacy and safety of labetalol in treatment of hypertension

The long-term efficacy and safety of labetalol, an antihypertensive agent with combined beta- and alpha-blocking activity, were evaluated alone (number = 193) and in combination with a diuretic (number = 144) in an open-label multicenter trial of 337 hypertensive patients aged 21 to 75 years, including initially 205 (61 percent) men and 219 (65 percent) Caucasians. There were 219 (65 percent) mild, 85 (25 percent) moderate, and 33 (10 percent) severe hypertensive patients. Labetalol (100 to 1,200 mg twice a day) alone or in combination with a diuretic reduced the mean standing blood pressure by 13/11 and 25/16 mm Hg to 135/88 and 130/91 mm Hg, respectively (p less than 0.01), and supine blood pressure by 6/7 and 18/13 mm Hg to 141/86 and 138/90 mm Hg (p less than 0.01), respectively. Blood pressure reductions observed at one month were maintained after one year; 206 (62 percent) patients had 10 mm Hg or greater reductions and 184 (56 percent) patients were maintained at diastolic blood pressures less than 90 mm Hg. Most frequently reported drug-related side effects included fatigue (14 percent), dizziness (12 percent), nausea (11 percent), nasal stuffiness (8 percent), headache (4 percent), and male sexual dysfunction (14 percent). Side effects were generally of mild to moderate intensity and often transient. In addition, in 27 (8 percent) patients reversible asymptomatic transaminase elevations to greater than twice normal developed at some time during the study. In 13 (4 percent) patients these alterations resolved during continued labetalol therapy, but in five (2 percent) patients these marked elevations led to discontinuation of the drug. A total of 32 (9.5 percent) patients were terminated prematurely due to side effects (most commonly genitourinary or gastrointestinal) possibly attributable to the drug. These findings indicate that labetalol with or without a diuretic is a potentially effective, safe, and relatively well-tolerated long-term antihypertensive therapy.

Metabolic and haemodynamic effects of increased circulating adrenaline in man. Effect of labetalol, an alpha and beta blocker

To simulate increased sympathoadrenal activity adrenaline was infused in normotensive subjects to achieve plasma adrenaline concentrations similar to those seen after myocardial infarction or hypoglycaemia. Adrenaline was infused after pretreatment for five days with labetalol 200 mg twice daily or placebo given in a random order. The rise in systolic blood pressure and the fall in diastolic blood pressure observed after the infusion of adrenaline (0.06 micrograms/kg/min) were prevented by labetalol and no increase in blood pressure was seen. Adrenaline infusion after pretreatment with placebo caused a profound fall in the serum potassium concentration (4.12-3.20 mmol(mEq)/l). Pretreatment with labetalol completely blocked adrenaline induced hypokalaemia (3.92-3.95 mmol(mEq)/l). Adrenaline induced T wave flattening and QTc prolongation were also prevented by labetalol. Thus labetalol can prevent the electrocardiographic, haemodynamic, and hypokalaemic effects of increased circulating adrenaline in man. The combination of alpha and beta blockade appears to be required to block the haemodynamic effects of adrenaline, and labetalol may, therefore, be useful in controlling both the metabolic and circulatory responses during increased sympathoadrenal activity.

Labetalol: an alpha- and beta-blocker

Labetalol is an investigational alpha- and beta- adrenoreceptor antagonist. The ratio of effective beta: alpha-blockade is approximately 7:1. Labetalol, administered intravenously or orally, has been effective in treatment of hypertension, with minimal effects on cardiac output. Labetalol will offer advantages over propranolol due to its more potent antihypertensive effects and less potent effects on left ventricular function at both rest and exercise in patients with coronary artery disease. The drug will be utilized in patients unresponsive to other beta-blocking agents and in patients with congestive heart failure and concomitant hypertension, angina, or arrhythmias when other beta-blockers are contraindicated. The drug appears to be safe in obstructive airway diseases and offers advantages over other beta-blockers in long-term treatment after myocardial infarction.

Labetalol: a review of its pharmacology, pharmacokinetics, clinical uses and adverse effects

Labetalol is a combined alpha- and beta-adrenoceptor blocking agent for oral and intravenous use in the treatment of hypertension. It is a nonselective antagonist at beta-adrenoceptors and a competitive antagonist of postsynaptic alpha 1-adrenoceptors. Labetalol is more potent at beta that at alpha 1 adrenoceptors in man; the ratio of beta-alpha antagonism is 3:1 after oral and 6.9:1 after intravenous administration. Labetalol is readily absorbed in man after oral administration, but the drug, which is lipid soluble, undergoes considerable hepatic first-pass metabolism and has an absolute bioavailability of approximately 25%. There are no active metabolites, and the elimination half-life of the drug is approximately 6 hours. Unlike conventional beta-adrenoceptor blocking drugs without intrinsic sympathomimetic activity, labetalol, when given acutely, produces a decrease in peripheral vascular resistance and blood pressure with little alteration in heart rate or cardiac output. However, like conventional beta-blockers, labetalol may influence the renin-angiotensin-aldosterone system and respiratory function. Clinical studies have shown that the antihypertensive efficacy of labetalol is superior to placebo and to diuretic therapy and is at least comparable to that of conventional beta-blockers, methyldopa, clonidine and various adrenergic neuronal blockers. Labetalol administered alone or with a diuretic is often effective when other antihypertensive regimens have failed. Studies have shown that labetalol is effective in the treatment of essential hypertension, renal hypertension, pheochromocytoma, pregnancy hypertension and hypertensive emergencies. In addition, preliminary studies indicate that labetalol may be of value in the management of ischemic heart disease. The most troublesome side effect of labetalol therapy is posture-related dizziness. Other reported side effects of the drug include gastrointestinal disturbances, tiredness, headache, scalp tingling, skin rashes, urinary retention and impotence. Side effects related to the beta-adrenoceptor blocking effect of labetalol, including asthma, heart failure and Raynaud's phenomenon, have been reported in rare instances.