Clinical pharmacology of the new beta-adrenergic blocking drugs. Part 2. Physiologic and metabolic effects

Hypertension in the elderly

The elderly are the most rapidly growing population group in the world. Data collected over a 30-year period have demonstrated the increasing prevalence of hypertension with age. The risk of coronary artery disease, stroke, congestive heart disease, chronic kidney insufficiency and dementia is also increased in this subgroup of hypertensives. Hypertension in the elderly patients represents a management dilemma to cardiovascular specialists and other practioners. During the last years and before the findings of the Systolic Hypertension in Europe Trial were published, the general medical opinion considered not to decrease blood pressure values similarly to other younger patients, in order to avoid possible ischemic events and poor oxygenation of the organs (brain, heart, kidney). The aim of this review article is to highlight the importance of treating hypertension in aged population in order to improve their quality of life and lower the incidence of the cardiovascular complications.

Levosimendan Does Not Improve Cardiac Output or Blood Pressure in a Rodent Model of Propranolol Toxicity When Administered Using Various Dosing Regimens

Background: Levosimendan (CAS: 141505-33-1) is a myocardial calcium sensitizer that improves myocardial contractility in various forms of heart failure. It produces a moderate improvement in cardiac output (CO) without an improvement in blood pressure (BP) in verapamil and metoprolol poisoned rodents. Aim: To assess the effect of various levosimendan dosing regimens on hemodynamics in a rodent model of propranolol poisoning. Method: Male Wistar rats (350-450 g) were anesthetized, ventilated, and instrumented to record BP, heart rate (HR), and CO. Propranolol was infused continually. When BP dropped to 50% of baseline rats received 1 of 7 treatments: (1) 0.9% saline (control), (2) levosimendan 36 μg/kg loading dose then 0.6 μg/kg per min, (3) levosimendan 0.6 μg/kg per min, (4) epinephrine 0.5 μg/kg per min, (5) levosimendan 70 μg/kg loading dose then 1.2 μg/kg per min, (6) levosimendan 1.2 μg/kg per min, and (7) levosimendan 70 μg/kg loading dose alone. Hemodynamics were recorded every 10 minutes for 70 minutes. Cardiac output, mean arterial pressure, and HR for each group were compared with control. Results: All groups had comparable baseline and maximal toxicity hemodynamics prior to initiation of treatment. Levosimendan did not improve CO or BP with any dosing regimen. Blood pressure tended to be lower than control for all doses of levosimendan. Epinephrine significantly improved BP but not CO compared to all other treatment groups. Survival did not differ between groups. Conclusions: Unlike in verapamil and metoprolol poisoning models, levosimendan did not improve CO or survival in propranolol poisoning. Epinephrine improved BP, but not CO, suggesting that its actions were due to peripheral vasoconstriction.

ADP-induced platelet aggregation and metoprolol treatment of myocardial infarction patients. A controlled study

The effect of metoprolol on platelet aggregation was investigated in a group of postmyocardial infarction (MI) patients. The study was double-blind and included 63 subjects; 30 patients were maintained on metoprolol and 33 received placebo treatment. Adenosine diphosphate (ADP)-induced platelet aggregation was carried out in each subject close to 4 weeks after the acute MI. It was demonstrated that metoprolol as compared to placebo did not influence ADP-induced platelet aggregation in the present clinical setting.

Current and future status of beta-blockers in the treatment of hypertension

Beta-adrenergic receptor blockers (beta-blockers) are effective and safe antihypertensive drugs, and have been recommended as first-line therapy for hypertension by all Joint National Committees (JNCs) for the prevention, detection, evaluation, and treatment of high blood pressure (BP) from the first to the last (JNC-7) in 2003. However, recently questions have been raised by several investigators regarding the antihypertensive effectiveness and safety of these drugs. The Medline literature on this subject was searched and pertinent studies were retrieved. Other pertinent references from existing publications were retrieved and analyzed up to 2007. Additionally, a historical perspective on the discovery of beta-blockers and their mechanism of action is given. Most of the reviewed short-term and long-term clinical trials demonstrate an effective and safe antihypertensive pattern for the beta-blockers. The weaknesses identified include the adverse effect of older beta-blockers on glucose control and stroke protection, especially in older persons. These adverse effects are attributed to their mechanism of action and BP effectiveness. On the basis of the evidence presented, beta-blockers are effective and safe antihypertensive drugs and should still be recommended as first-line therapy in most uncomplicated hypertensive patients, either alone or in combination with other drugs. There are reservations regarding their administration to diabetic and older hypertensive patients. However, when compelling indications for their use exist, they should not be withheld.

Cardiovascular and respiratory considerations with pharmacotherapy of glaucoma and ocular hypertension

Glaucoma and ocular hypertension are highly prevalent conditions in individuals over the age of 40 and are commonly seen together in patients with cardiovascular disease. Many of the antiglaucoma medications, when systemically absorbed, affect the sympathetic and parasympathetic nervous systems of patients and can cause cardiovascular toxicity. Such adverse effects are frequently associated with the long-term use of potentially toxic agents in elderly people, who are most prone to chronic eye disease. Moreover, patients may not associate their symptoms with the topical eye medications, and consequently may not report adverse drug effects. Drug-drug interactions can also occur when patients are taking medications for both cardiovascular disease and glaucoma. In this review, the systemic toxicity of these agents is reviewed, along with possible drug-drug interactions. Mention is made of other antiglaucoma medications used alone and in combination with topical beta-blockers. Identification of genetic loci-a bold new step toward glaucoma treatment-is mentioned briefly at the end of the article.

Are 1–2 tablets dangerous? Beta-blocker exposure in toddlers

The common use and wide availability of beta-adrenergic blocking agents make them frequent ingestants for small children. Yet, there are no clear guidelines in the literature to direct the care of the toddler with the history of ingesting 1-2 tablets. With 40 years of extensive clinical experience, not one documented case of death or serious cardiovascular morbidity as a direct result of a beta-blocker exposure is to be found in an English language review for children under 6 years of age. As with children on chronic beta-blocker therapy, several cases of symptomatic hypoglycemia associated with a single acute propranolol exposure suggest a vulnerability to this complication. Though the risk to the toddler exposed to 1-2 tablets appears to be extremely small, several factors mitigate the actual risk to the child and the need for triage to a health care facility.

Monotherapy versus combination therapy as first line treatment of uncomplicated arterial hypertension

Mild to moderate hypertension still remains poorly controlled. This relates to multiple factors including low antihypertensive efficacy of single drug therapies reluctance of primary care physicians to modify/titrate initially chosen therapy to obtain target blood pressure, and poor compliance with medication. Several guidelines for the treatment of high blood pressure now include combination therapy with low doses of 2 drugs as one of the strategies for the initial management of mild/moderate arterial hypertension. Evidence discussed in this article points to superior control of blood pressure by combinations of low doses of 2 drugs as compared with monotherapy in regular doses. This superior effectiveness of combined therapy relates to a better antihypertensive efficacy and higher response rates in the low range of doses as the result of complementary mechanisms of antihypertensive effects, better tolerance as a result of a lower rate of adverse effects in the low dose range, improved compliance from better tolerance and simple drug regimen, and lower cost. Whether increased use of fixed low dose combination therapies would translate to better control of arterial hypertension in the population and thereby further reduction of cardiovascular/cerebrovascular morbidity and mortality caused by hypertension remains to be assessed.

Cardiovascular considerations in using topical, oral, and intravenous drugs for the treatment of glaucoma and ocular hypertension: focus on beta-adrenergic blockade

Glaucoma and ocular hypertension are highly prevalent conditions in individuals over the age of 40 and are commonly seen together in patients with cardiovascular disease. Many of the antiglaucoma medications, when systemically absorbed, affect the sympathetic and parasympathetic nervous systems of patients and can cause cardiovascular toxicity. Such adverse effects are frequently associated with the long-term use of potentially toxic agents in elderly people, who are most prone to chronic eye disease. Moreover, patients may not associate their symptoms with the topical eye medications, and consequently may not report adverse drug effects. Drug-drug interactions can also occur when patients are taking medications for both cardiovascular disease and glaucoma. This review focuses on beta-adrenergic blockers as topical antiglaucoma medications and other topical antiglaucoma drugs. The systemic toxicity of these agents is reviewed, along with the possible drug interactions. Brief mention is also made of other antiglaucoma medications used alone and in combination with topical beta-blockers.

Tissue perfusion in relation to cardiac output during continuous positive-pressure ventilation and administration of propranolol or verapamil

BACKGROUND

Our objective was to determine whether administration of propranolol or verapamil modifies the hemodynamic adaptation to continuous positive-pressure ventilation (CPPV), in particular the regional distribution of cardiac output (CO).

METHODS

General hemodynamics and regional blood flows assessed by microsphere technique (15 microns) were recorded in 16 anesthetized pigs during spontaneous breathing (SB) and CPPV with 8 cm H2O end-expiratory pressure (CPPV8) before and after intravenous administration of propanolol (0.3 mg.kg-1 followed by 0.15 mg.kg-1.h-1, n = 8) or verapamil (0.1 mg.kg-1 followed by 0.3 mg.kg-1.h-1, n = 8).

RESULTS

CPPV8 depressed CO by 25% without shifts in its relative distribution with the exception of a noteworthy increase in adrenal perfusion. Propranolol increased arterial blood pressure, and due to a fall in heart rate, CO dropped by 25%. The kidneys and, to a lesser extent, the splanchic region and central nervous system received increased fractions of the remaining CO at the expense of skeletal muscle flow. Similar patterns were seen during SB and CPPV8 such that the combination of propranolol and CPPV8 depressed CO by 50%. The circulatory effects of verapamil were less evident but myocardial perfusion tended to increase.

CONCLUSIONS

The combination of propranolol or verapamil with CPPV does not result in any specific hemodynamic interaction in anesthetized pigs, except that the combined effect of propranolol and CPPV may severely reduce CO.

Long-term efficacy and safety of atenolol for supraventricular tachycardia in children

Propranolol, a first-generation nonselective beta-adrenoceptor blocking agent, is commonly used to treat pediatric arrhythmias. Atenolol, relatively long-acting, cardioselective beta-adrenoceptor blocking agent, has been successfully used in adults with supraventricular tachycardia (SVT). There is only one report on the use of atenolol in children with SVT; and our report is on the first long-term prospective study to evaluate the use of atenolol in children. A group of 22 children < 18 years of age with clinical SVT were enrolled in the study. The tachycardia was documented on electrocardiograms in each case and was confirmed by electrophysiologic studies in some. Once-a-day oral atenolol was started as a monotherapy. Of the 22 children with various types of SVT, 13 (59%) were well controlled on long-term oral atenolol therapy. The effective dose of atenolol ranged between 0.3 and 1.3 mg/kg/day (median effective dose 0.7 mg/kg/day). Five children had some adverse effects. However, none in the successful group of 13 patients required drug discontinuation because of such effects. Once-a-day oral atenolol as a monotherapy is effective and relatively safe for long-term management of SVT during childhood. It is an attractive alternative beta-adrenoceptor blocking agent for the management of pediatric arrhythmias.

Bioequivalence of two tablet formulations of nadolol using single and multiple dose data: assessment using stereospecific and nonstereospecific assays

Nadolol, a nonspecific beta-blocker, is a racemate composed of equal amounts of four stereoisomers, namely, SQ-12148, SQ-12149, SQ-12150, and SQ-12151. In an open-label, randomized, four-period crossover study, the pharmacokinetics of nadolol and its stereoisomers and the bioequivalence of two formulations of nadolol were assessed in 20 healthy male subjects following a single dose (80 mg) and multiple doses (80 mg; once daily for 7 days). A standard granulated tablet and direct compressed tablet formulations, each containing 80 mg of nadolol, with different in vitro dissolution profiles that met current USP requirements were used. The four treatments were single and multiple doses of granulated tablet, and single and multiple doses of compressed tablet. There was a 7 day washout period between successive treatments. All doses of nadolol were administered after an overnight fast. Serial blood samples were collected up to 72 h following the single dose and during multiple dose treatments, following day 6 and 7 doses. Validated high-performance liquid chromatographic assays were applied to measure nadolol and its stereoisomers in the study samples. Plasma concentration data were subjected to noncompartmental pharmacokinetic analysis. Both C(max) and AUC values were significantly greater for SQ-12150 when compared to other nadolol stereoisomers obtained after a single dose or at steady state. However, T(max) and T1/2 values were similar among the four isomers. The observed steady state AUC tau values for nadolol (2278-2331 ng h/ML) or its stereoisomers (550-874 ng h/ML) were significantly greater than those predicted from the single dose AUCinf values (nadolol, 1840-1845 ng h/ML; isomers, 450-713 ng h/ML). The intrasubject variability, computed from multiple dose data, was generally greater for the stereoisomers (17-40%) than for nadolol (10-32%). The two formulations were bioequivalent for nadolol (C(max) = 0.98 [84%, 117%]; AUCinf = 1.03 [93%, 116%]) and SQ-12150 (C(max) = 1.12 [89%, 122%]; AUCinf = 0.98 [82%, 119%]) after a single dose, and only for nadolol (C(max) = 1.07 [84%, 118%]; AUCinf = 1.02 [91%, 113%]) at steady state.

Topical ophthalmic beta-adrenergic blockade for the treatment of glaucoma and ocular hypertension

Since the late 1970s, topical beta-adrenergic blockers have been the drugs of choice in treating ocular hypertension and associated glaucoma. The currently available drugs are timolol, betaxolol, levobunolol, metipranolol, and carteolol. All reduce intraocular pressure by decreasing the production of aqueous humor. Although these drugs are applied locally in the eye, they may enter the general circulation and reach concentrations high enough to cause systemic effects, including alterations in heart rate and rhythm, bronchoconstriction, dyslipidemia, and central nervous system abnormalities. Interactions with other drugs may also occur. Ocular beta- blockers differ in beta 1-selectivity (betaxolol is beta 1-selective, whereas the other drugs are nonselective) and in intrinsic sympathomimetic activity (ISA) or partial agonist properties (only carteolol possesses ISA). These differences give betaxolol and carteolol potential advantages in minimizing certain side effects. The advantage of betaxolol vis-à-vis systemic side effects is more clearly established than that of carteolol. Further systematic study is needed to determine what advantages, if any, are conferred by the presence of ISA.

Toxicity of beta-blockers in a rat whole embryo culture: concentration-response relationships and tissue concentrations

Beta-adrenoceptor blockers are widely used drugs for the treatment of cardiovascular diseases. Since beta-blockers cross the placenta, it is essential to consider possible adverse effects on the embryo. Six beta-adrenoceptor blockers were tested at various concentrations (10-5000 microM) in a rat whole embryo culture. Although inducing a very similar pattern of dysmorphogenetic effects (incomplete flexure, disturbed development of the neural tube, the head, the heart and the tail bud), the compounds exhibited a wide range of embryotoxic potency. Estimation of the EC50 (median-concentration producing dysmorphogenesis in 50% of the embryos) for the six compounds revealed differences of more than two orders of magnitude: propranolol 25 microM, alprenolol 30 microM, metoprolol 100 microM, pindolol 150 microM, acebutolol 500 microM, atenolol 4000 microM. Measurements of the concentrations of the various drugs in the cultured embryos at corresponding EC50 levels showed differing values: metoprolol 4.5 microM, propranolol 5.2 microM, alprenolol 8.4 microM, pindolol 9.0 microM, acebutolol 12.5 microM and atenolol 77.0 microM. With regard to the EC50 and the degree of substance transfer to the embryo it can be stated that propranolol and metoprolol show a much higher intrinsic potency to interfere with normal in vitro embryonic development than, e.g. atenolol.

Intranasal delivery of cardiovascular agents: an innovative approach to cardiovascular pharmacotherapy

The intranasal administration of drugs has long been used for the topical treatment of various nasal disorders. Many features of the intranasal mucosa also make it useful for delivery of systemically active agents. It has been shown that intranasal drug administration can provide plasma drug levels similar to those observed with comparable doses of parenteral drugs. The feasibility of intranasal administration of propranolol, nifedipine, and nitroglycerin has been investigated in several small clinical studies. Intranasal propranolol has been shown to improve exercise tolerance in patients with angina pectoris. Intranasal nifedipine has been used to treat patients with perioperative hypertension and hypertensive crisis. Intranasal administration of nitroglycerin was shown to blunt the hypertensive response to endotracheal intubation. These studies and others suggest that intranasal delivery of cardiovascular drug treatment could be used in those clinical situations where a rapid or intermittent drug effect is desired and can potentially serve as an alternative to parenteral drug administration.

Possible involvement of ATP-sensitive K+ channels in the inhibition of rat central adrenergic neurotransmission under hypoxia

By using rat brain cortical slices preloaded with [3H]norepinephrine, we examined whether ATP-sensitive K+ channels are involved in altered adrenergic neurotransmission during hypoxia. The tritium overflow evoked by transmural nerve stimulation (TNS) was significantly inhibited at 5 min of hypoxia and reached the maximum inhibition at 20 min. The inhibition of the TNS-evoked tritium overflow under a 20-min hypoxia was reversed by subsequent reoxygenation and was concentration-dependently antagonized by glibenclamide (0.1 and 1 microM). 86Rb+ efflux was increased after introduction of hypoxia and reached the peak value at about 20 min, which was concentration-dependently antagonized by glibenclamide (0.1-10 microM). Hypoxia decreased cortical ATP content. Linear correlations were mutually observed among the changes by hypoxia in the TNS-evoked tritium overflow, tissue ATP content and 86Rb+ efflux. The spontaneous tritium outflow was inhibited only after hypoxic periods of more than 16 min, the inhibition being reversed by reoxygenation and antagonized by 1 microM glibenclamide. These results suggest that the inhibition of rat central adrenergic neurotransmission during hypoxia may be associated with an activation of ATP-sensitive K+ channels.

Pharmacokinetics of nadolol in children with supraventricular tachycardia

The pharmacokinetics of intravenous and oral nadolol, a long-acting beta-adrenoceptor blocking agent, were investigated in six children receiving the drug for treatment of supraventricular tachycardia. In the youngest patient (age 3 months), no distribution phase was seen. In children younger than 22 months of age, nadolol is more rapidly eliminated (t1/2 = 4.3 hours or less) than in older children, in whom elimination is more similar to that in adults (t1/2 approximately 7.3-15.7 hours). After intravenous administration, nadolol displayed two-compartment pharmacokinetics with a distribution phase (t1/2 = 0.2-1.1 hours) followed by elimination. Large changes in nadolol pharmacokinetics may occur during the first year of life. Nadolol should be used cautiously in infants.

Efficacy and safety of intravenous and oral nadolol for supraventricular tachycardia in children

The efficacy and safety of oral nadolol in supraventricular tachycardia were evaluated prospectively in 27 children (median age 5.5 years). Fifteen patients had an unsuccessful trial of digoxin therapy. Intravenous nadolol was given to seven patients during electrophysiologic study; five of these had an excellent response and two had a partial response (25% decrease in tachycardia rate). Six of these patients had a similar response to oral nadolol. Twelve patients received both propranolol and nadolol. Among six patients, intravenous propranolol was successful in four and unsuccessful in two; all six had a similar response to oral nadolol. With oral propranolol, tachycardia was well controlled in four patients and persistent in two; five of five patients had a similar response to oral nadolol. Twenty-six patients were treated with oral nadolol; the arrhythmia was well controlled in 23, 2 had recurrent tachycardia and 1 patient had tachycardia at a 25% slower rate. The effective dose of nadolol ranged between 0.5 and 2.5 mg/kg body weight once daily (median dose 1 mg/kg per day). During follow-up (3 to 36 months), compliance and tolerance were excellent; excluding 2 patients with reactive airway disease who developed wheezing, only 3 (12%) of 24 had side effects necessitating a change in drug therapy. Once a day nadolol is a safe and effective agent in the management of supraventricular tachycardia in children. Its long-term efficacy can be predicted by the short-term response to intravenous nadolol or propranolol during programmed electrophysiologic study.

Controlled release metoprolol formulations. A review of their pharmacodynamic and pharmacokinetic properties, and therapeutic use in hypertension and ischaemic heart disease

Conventional formulations of metoprolol have become well established in cardiovascular medicine and are particularly useful in the management of hypertension and ischaemic heart disease. Recently developed controlled release metoprolol delivery systems (metoprolol CR/ZOK and metoprolol OROS) were designed to overcome the drug delivery problems of matrix-based sustained release forms by releasing the drug at a relatively constant rate over a 24-hour period, and thus producing sustained and consistent metoprolol plasma concentrations and beta 1-blockade while retaining the convenience of once daily administration. Clinically and statistically significant reductions in blood pressure have been observed with metoprolol CR/ZOK and metoprolol OROS 24 hours after administration in mildly or moderately hypertensive patients. Studies in patients with mild to moderate hypertension have demonstrated that a similar or higher percentage of patients achieved a goal response with metoprolol CR/ZOK compared with matrix-based sustained release formulations of metoprolol, or conventional atenolol or bisoprolol, while metoprolol OROS achieved an equal or greater response rate compared with conventional or matrix-based sustained release metoprolol preparations. In patients with stable effort angina pectoris, once daily administration of metoprolol CR/ZOK provided at least equal antianginal efficacy as conventional metoprolol in divided doses, while metoprolol OROS reduced the mean number of anginal attacks by the same margin as atenolol. Controlled release metoprolol formulations have been well tolerated in clinical trials. Metoprolol CR/ZOK was associated with a similar or lesser degree of adverse effects related to the central nervous system compared with atenolol or long acting propranolol. Metoprolol CR/ZOK also demonstrated less pronounced beta 2-mediated bronchoconstrictor effects than atenolol in asthmatics, and less general fatigue and leg fatigue in healthy subjects. Metoprolol OROS produced less pronounced bronchoconstrictor effects than atenolol, matrix-based sustained release metoprolol or long acting propranolol in patients with asthma or obstructive airways disease, and healthy volunteers. These results are presumably due to the beta 1-selectivity of metoprolol in addition to the relatively low plasma concentrations maintained by metoprolol CR/ZOK and metoprolol OROS, and the avoidance of high peak plasma concentrations with these agents. Despite the relative safety of the controlled release forms of metoprolol, the use of all beta-adrenoceptor antagonists should be avoided in patients with a history of bronchospasm. Thus, controlled release metoprolol formulations offer the potential to maximise the confirmed benefits of this agent in the management of hypertension and angina, by maintaining clinically effective plasma concentrations within a narrow therapeutic range over a 24-hour dose interval.

Clinical use of beta-adrenoceptor blockade in systemic hypertension

beta-Blockers are effective in reducing the blood pressure of many patients with systemic hypertension. They differ in terms of the presence or absence of intrinsic sympathomimetic activity, membrane-stabilising activity, beta 1-selectivity, alpha-blocking properties, and relative potency and duration of action. All beta-blockers appear to have blood pressure lowering effects. The choice of which beta-blocker to use in an individual patient is determined by the pharmacodynamic and pharmacokinetic differences between the drugs in conjunction with the patient's other medical condition(s). This review discusses the practical use of beta-blockers and provides rational suggestions for which drug(s) to use in selected patient groups (Black, elderly, postinfarction, diabetes, renal disease, obstructive lung disease, elevated lipid levels, coexisting angina, and left ventricular hypertrophy).

Racial differences in drug response: isoproterenol effects on heart rate in healthy males

It was the purpose of this study to investigate racial alterations in beta-adrenoceptor response. Two groups of healthy, male volunteers gave their consent. There were eight black Americans (mean age, 26.1 +/- 2.5 years) and eight white/Caucasian Americans (mean age 24.4 +/- 1.8 years). Each subject underwent an isoproterenol sensitivity test. There was a significant (P less than 0.05) decrease in the ratio of Emax to ED50 in the white group (25.3 +/- 6.4) compared with the black group (37.1 +/- 12.4). Over the dose range of 0.1 to 1.0 micrograms there was a significant increase in response at both the 0.25- and the 0.5-microgram dose (P less than 0.05), with the black American group appearing to respond with a greater rate of rise in heart rate following the initial doses.

Pharmacodynamic comparison of L-bunolol with propranolol, metoprolol, and placebo

Twelve healthy volunteers received single oral doses of propranolol (80 mg), metoprolol (100 mg), L-bunolol (2 mg), and placebo in a four-way crossover study. Blood pressure, ventricular rate, and echocardiographically determined ejection fraction, ejection time, and mean rate of circumferential fiber shortening (mVcf) were measured before dosing and at multiple time points during 10 hours after each dose, with subjects maintained in the supine position. Reductions in systolic and diastolic blood pressure following administration of each of the beta blockers were greater than those observed with placebo, but differences among the four treatments were not significant. Heart rate reductions with the beta blockers differed significantly from placebo (P less than .001), but differences among the three beta blockers were not significant. Differences among the four treatments in mVcf decrement did not attain significance at the 5% level (.05 less than P less than .1), and there were no significant differences in ejection-time prolongation or ejection-fraction reduction. Thus, reduced blood pressure, heart rate slowing, and reduced cardiac contractility may be associated with placebo treatment and may indicate the need for placebo controls in studies of the cardiovascular effects of beta blockers. Despite differing secondary pharmacologic properties, the three beta blockers reduced heart rate to a similar extent. Other effects of the beta blockers on blood pressure and cardiac contractility could not be consistently distinguished from those associated with placebo.

Concentration-effect relationships for oxprenolol in patients with essential hypertension

1. Plasma drug concentrations, and heart rate and blood pressure responses to exercise at a predetermined load were examined in twelve hypertensive patients following single and repeated doses of oxprenolol administered once daily as oral osmotic drug delivery systems (10/170 and 16/260 oxprenolol OROS). 2. Plasma oxprenolol concentration profiles after each preparation were consistent with the criteria for sustained drug release. Levels immediately after exercise were significantly higher than those prior to exercise (P less than 0.001), but differences were slight. 3. Both OROS drug forms reduced exercise heart rate for 24 h after single and repeated doses; effects were greater for 16/260 OROS than for 10/170 OROS. Significant reductions in post-exercise systolic BP were observed 24 h after drug administration and after repeated doses there was little difference between the preparations. Effects on diastolic BP after exercise were slight. 4. The relationship between plasma oxprenolol concentrations and exercise heart rates fitted an exponential mathematical model which makes allowance for inter-individual variability. No such kinetic-dynamic relationship could be defined for post-exercise systolic or diastolic BP.

Clinical significance of beta 1-selectivity and intrinsic sympathomimetic activity in a beta-adrenergic blocking drug

Almost all beta-adrenergic blockers, regardless of their pharmacologic characteristics, appear to have blood pressure-lowering activity in hypertensive patients. Comparisons between nonselective beta-blocking agents, such as propranolol and nadolol, with beta 1-selective drugs, such as metoprolol, atenolol and acebutolol, have demonstrated close similarities in their antihypertensive effects in patients. Similarly, beta blockers with and without intrinsic sympathomimetic activity (ISA) have comparable antihypertensive effects. However, beta-selective agents may offer some advantages over conventional beta blockers in hypertensive patients with concurrent conditions such as chronic obstructive airways disease, peripheral vascular disease, diabetes and hyperlipidemia. Beta 1-selective drugs are also preferred in diabetic patients receiving hypoglycemic agents because they do not interfere with glycogenolysis. Agents lacking ISA, such as propranolol, acutely increase peripheral resistance. beta blockers with ISA usually lower resistance. ISA may also minimize the bradycardia frequently found in elderly patients. Agents with ISA may protect against the decrease in high density lipoprotein cholesterol and the modest increase in triglycerides noted with some beta blockers that do not have ISA. Thus, in a large number of clinical situations in which hypertension is found, the properties of beta 1 selectivity and ISA allow beta blockers to be used with greater safety. Therefore, agents possessing both of these properties may be particularly valuable.

Beta-adrenergic blocker withdrawal

Abrupt withdrawal of long-term beta-blocker therapy in patients with angina may be associated with unstable angina and myocardial infarction. It appears that an "overshoot" in heart rate from pretreatment values occurs, which increases myocardial oxygen demand. This increase in heart rate may be secondary to increased beta receptor numbers or increased receptor sensitivity. Another possible mechanism for the increased risk of myocardial infarction after beta-blocker withdrawal is increased platelet aggregability. Withdrawal reactions may be less severe with beta blockers that have partial agonist activity. In patients undergoing coronary artery bypass surgery, beta-blocker withdrawal reactions have also been observed. Maintenance of beta-blocker therapy on the morning of surgery appears to reduce this risk. Gradual withdrawal regimens in outpatients with angina may be associated with lower risk for a beta-blocker withdrawal reaction. The gradual withdrawal of beta blockers in hypertensive patients requires further study.

Carotid sinus reflexes in rats given small doses of lead

The effect of low level lead poisoning on the carotid sinus reflex in rats was studied. The reflex was evoked by carotid artery clamping, in control and lead-poisoned animals. Wistar rats were given lead acetate trihydrate (50 mg/kg) via stomach tube once weekly for 5 weeks; control animals were given equimolar amounts of sodium acetate. Both groups were fed a regular animal food diet. At the end of the 6th week, and under urethane anesthesia, mean arterial blood pressure and heart rate were continuously recorded for both groups, before and after clamping, and after unclamping the left common carotid artery. In other experiments, some animals were pre-treated with dopamine, 0.040 mg/kg; practolol, 3 mg/kg; propranolol, 0.1 mg/kg; or atropine, 0.1 mg/kg. In animals not given drugs, lead produced a less pronounced rise in mean arterial blood pressure after clamping, and a more pronounced decrease in heart rate after unclamping, compared to control animals. Some drugs altered this response pattern. Atropine led to a more pronounced tachycardia in the lead-poisoned rats, whereas practolol led to a more pronounced bradycardia in the lead-poisoned rats. Propranolol pretreatment led to a less pronounced decrease in heart rate for lead-poisoned rats, again as compared to the controls. Atropine and beta-adrenergic receptor blocking agents produced similar carotid sinus reflex responses in control and lead-poisoned animals.

Mortality in the beta blocker heart attack trial: circumstances surrounding death

In the Beta Blocker Heart Attack Trial, a double blind, randomized, controlled study, patients taking propranolol (180 or 240 mg/day) initiated 5-21 days post myocardial infarction had 26% fewer deaths than those taking placebo over a 25 month (mean) followup. Detailed analysis of the circumstances surrounding the BHAT deaths failed to reveal any striking difference between propranolol and placebo in the type of clinical event preceding death, the incidence and type of acute and prodromal signs and symptoms, the location of death, the activity preceding death or the percentage of deaths that were sudden or instantaneous, suggesting that propranolol may exert an "across the board" effect and improve survival by a combination of mechanisms. An unexpected finding was that the protective effect of propranolol appeared to occur during the hours of 10 p.m. to 7 a.m.

Acute, short- and long-term efficacy of oral bevantolol in patients with coronary artery disease: a placebo-controlled, randomized, double-blind study

The efficacy and safety of bevantolol (new cardioselective beta-blocking agent without intrinsic sympathetic activity) were evaluated in chronic stable angina pectoris. Acute effects on heart rate (HR) and pulmonary function (forced expiratory volume in the first second, FEV1, and vital capacity, VC) (double-blind placebo, propranolol, 80 mg, and bevantolol, 150 mg) and the antianginal efficacy during early (double-blind placebo period) and chronic bevantolol therapy (long-term follow-up for 52 weeks) were studied. Bevantolol reduces HR in the same way as propranolol (both p less than 0.01). Pulmonary function is modified significantly only by propranolol (decreasing FEV1, p less than 0.05). Bevantolol reduces antianginal attacks and nitroglycerin consumption (p less than 0.01) and improves exercise tolerance (p less than 0.01) during early and chronic therapy.

Labetalol in the treatment of essential hypertension: a single-blind dose ranging study

The hypotensive efficacy of labetalol was evaluated in 29 patients with essential hypertension in a single-blind dose ranging study. After a two-week period of placebo treatment, labetalol was given in oral doses of 0.6 g/d, 0.8 g/d, and 0.8 g/d combined with 25-50 mg/d of hydrochlorothiazide. Each regimen lasted four weeks. The decrease in blood pressure was dose dependent: 90% of patients showed a significant reduction in diastolic blood pressure and 75% showed a significant reduction in systolic blood pressure. In 69% of the patients, side effects of the drug were noted, and in five patients (17%), treatment was discontinued because of the side effects. Seven patients received labetalol intravenously before the oral treatment. Their heart rate and blood pressure reductions were similar to those found in patients only taking the medication orally. We conclude that labetalol is an efficient and safe antihypertensive agent in both oral and intravenous administration. However, the high incidence of side effects makes labetalol a drug of second choice in uncomplicated hypertensive patients.

An office-based primary care trial of pindolol ('Visken') in essential hypertension

A large, open, multi-centre study was performed by physicians in general practice to evaluate the efficacy and tolerance of pindolol (10 to 20 mg per day) in the treatment of patients with essential hypertension. The records of 7324 patients who completed the 6-week protocol with pindolol alone or in combination with a diuretic were analyzed by computer. Substantial reductions in both systolic and diastolic blood pressure were obtained in the majority of patients regardless of age, sex or race. No difference in blood pressure response was found between patients taking diuretics concurrently and those on pindolol alone. Side-effects were generally not troublesome and a trend toward a reducing incidence of side-effects was noted in all patients as the duration of therapy increased. Black patients tended to complain of fewer side-effects than did white patients.

Anion-channel blockade with alinidine: a specific bradycardic drug for coronary heart disease without negative inotropic activity?

In 14 patients undergoing cardiac catheterization for suspected coronary artery disease, alinidine, 0.6 mg/kg, was administered intravenously to determine its effects on left ventricular (LV) function, coronary blood flow and myocardial oxygen consumption. To assess effects independent of changes in heart rate (HR), measurements were made at spontaneous and matched pacing HRs. At spontaneous HR, alinidine decreased HR from 70 +/- 2 to 61 +/- 3 beats/min (p less than 10(-6]. Peak rate of LV pressure decreased from 1,652 +/- 92 to 1,371 +/- 80 mm Hg/s (p less than 10(-5] and Vmax decreased from 47 +/- 3 to 41 +/- 2 s-1 (p less than 10(-4]. Coronary sinus blood flow decreased from 109 +/- 9 to 89 +/- 7 ml/min (p less than 0.01) and myocardial oxygen consumption from 10.9 +/- 1.0 to 9.0 +/- 0.8 ml O2/min (p less than 0.05). At a matched pacing HR of 98 +/- 3 beats/min before and after alinidine administration, peak rate of LV pressure decreased from 1,984 +/- 124 to 1,793 +/- 106 mm Hg/s (p less than 10(-4] and Vmax from 60 +/- 5 to 56 +/- 4 s-1 (p less than 0.02). Coronary sinus blood flow and myocardial oxygen consumption were not significantly changed at matched pacing HRs. The time constant of the first 40 ms of LV isovolumic relaxation was prolonged by alinidine only during spontaneous HR. Thus, alinidine results in a bradycardia-dependent decrease in myocardial oxygen consumption. It has negative inotropic properties independent of changes in HR and so is not a pure bradycardia-specific agent.

Beta-adrenergic blockade may prolong life in post-infarction patients in part by increasing vagal cardiac inhibition

Beta-adrenergic blocking drugs prolong lives of post-infarction patients primarily by preventing sudden cardiac death. The mechanisms responsible for this beneficial effect are not understood clearly, since beta-blockers, in doses used in most clinical trials, are only weakly effective against stable ventricular arrhythmias. Arrhythmias during myocardial ischemia may differ from arrhythmias in other clinical settings in that they depend importantly upon autonomic neural factors, including the balance between levels of sympathetic cardiac stimulation and parasympathetic cardiac inhibition. Beta-blockers reduce sympathetic cardiac stimulation, and they may influence this balance favorably in another important way: a well documented, but not generally appreciated property of beta-blocking drugs is that they also increase levels of vagal cardiac inhibition. I propose that beta-blockade prevents arrhythmic deaths in post-infarction patients in part by increasing levels of vagal cardiac inhibition.

Mechanisms of action and the clinical pharmacology of beta-adrenergic blocking drugs

At present more than 20 beta-adrenergic blocking drugs are commercially available in Western Europe, and six are available in the United States. The clinical indications for their usage include hypertension, arrhythmias, ischemic heart disease, thyrotoxicosis, migraine headaches, glaucoma, and anxiety states. We will review the mechanisms suggested for the antihypertensive action of beta-adrenergic blocking drugs as well as these agents' clinical pharmacologic aspects. In general, the pharmacodynamic effects of the beta blocking drugs are quite similar, yet the properties of biotransformation, including pharmacokinetics, tend to be distinguishing features.

Basic understanding of the electrophysiologic actions of antiarrhythmic drugs. Sources, sinks, and matrices of information

The author creates an intellectual framework consisting of key electrophysiologic principles, basic mechanisms of arrhythmogenesis, and important drug reactions that will allow the rational use of antiarrhythmic drugs. Basic principles have been emphasized because current understanding requires it.

Sinus node function and dysfunction

The wide range of normal sinus node function makes identification of dysfunction difficult. Emphasis is placed upon real time correlation of ECG bradyarrhythmia with typical symptoms. A spectrum of atrial electrical dysfunction is described which includes abnormalities of the sinus and AV nodes as well as failure of escape pacemakers and atrial tachyarrhythmias.

Beta-blocking drugs for arrhythmias, hypertension, and ischemic heart disease

Beta-blocking drugs have provided significant improvement in the medical therapy of many types of heart disease. They are more effective in treating young hypertensive patients than elderly hypertensive patients. These drugs reduce the ventricular rate seen in atrial flutter and fibrillation, and they also reduce the frequency of ventricular ectopy. Beta blockers are important adjuncts for control of angina pectoris. When these drugs are given for a period of 1 to 3 years after myocardial infarction they reduce the incidence of reinfarction and the frequency of sudden death as well as reduce the overall mortality rate. Factors that may contribute to the overall decreased mortality include the reduction in the reinfarction rate and an increased threshold for ventricular fibrillation as well as those mechanisms that reduce myocardial oxygen utilization.

Effects of labetalol on left ventricular mass and function in hypertension--an assessment by serial echocardiography

We determined echocardiographic (M-mode) indices of left ventricular mass and function serially at 1-month intervals in 10 patients with uncomplicated mild or moderate essential hypertension, before and after adequate control of blood pressure with labetalol, a combined alpha- and beta-receptor blocking agent. Seven patients had pretreatment echocardiographic evidence of left ventricular hypertrophy with disproportionate septal thickness in 4. Systolic blood pressure in the untreated state correlated well (r = 0.96) with left ventricular mass but poorly (r = 0.30) with diastolic pressure. Following a satisfactory blood pressure reduction, achieved in all patients, left ventricular mass decreased from 240.5 +/- 71.1 g to 159.5 +/- 40.7 g (P less than 0.01), interventricular septal thickness from 1.33 +/- 0.3 cm to 0.92 +/- 0.25 cm (P less than 0.01) and posterior wall thickness from 1.03 +/- 0.23 cm to 0.93 +/- 0.23 cm (P less than 0.05). While the maximum changes in left ventricular mass were noted by the end of first month (P less than 0.01) with insignificant changes thereafter, the correlation of fall in blood pressure with change in left ventricular mass was significant only after 2 months of treatment (P less than 0.05). Indices of left ventricular function (end-diastolic volume, ejection fraction, fractional diameter shortening, left atrial dimension and posterior aortic wall motion) were normal before treatment and remained unchanged during 3 months of treatment. In this short-term study, labetalol reduced left ventricular hypertrophy (expressed as left ventricular mass and wall thickness) without altering left ventricular function indices in patients with uncomplicated essential hypertension. This has important implications in the treatment of hypertensive patients.

Multiclinic comparison of labetalol to metoprolol in treatment of mild to moderate systemic hypertension

The antihypertensive effects of oral labetalol, a new alpha- and beta-adrenergic blocking agent, and metoprolol, a relatively beta1 selective adrenergic blocker, were evaluated in 91 patients with mild to moderate hypertension (standing diastolic blood pressure of 90 to 115 mm Hg) in a double-blind parallel group multicenter clinical trial. The effects of the two drugs on plasma lipids and lipoprotein fractions were also assessed. Following a four-week placebo phase, 44 patients were randomized to receive labetalol and 47 metoprolol. During a four-week titration phase, the labetalol dose was increased from 100 mg twice daily to a maximum of 600 mg twice daily to achieve a standing diastolic blood pressure of 90 mm Hg that was decreased by 10 mm Hg or more. Metoprolol was titrated from 50 mg to 200 mg twice daily. An eight-week maintenance period followed during which hydrochlorothiazide could be added. At the end of the maintenance phase, the doses of labetalol and metoprolol were tapered over a two to four day period after which patients received a placebo for one week. Blood pressure in the supine and standing position was measured at each visit. Labetalol and metoprolol both significantly (p less than 0.01) lowered the supine and standing blood pressure from baseline with no significant difference found between the two treatment groups. Both drugs lowered the heart rate; however, the rate-lowering effect was significantly greater with metoprolol (p less than 0.01). There were no significant effects of either drug on plasma lipids or lipoprotein fractions. Fatigue was the most frequently reported complaint with both drugs. Dizziness, dyspepsia, and nausea were more common with labetalol; bradycardia was more common with metoprolol. There was no blood pressure "overshoot" after withdrawing drug treatment; however, a heart rate "overshoot" was seen after metoprolol was tapered off and stopped. Labetalol is as safe and effective as metoprolol in the treatment of patients with mild to moderate hypertension.