Hypertension: which beta-blocker?

Efficacy of beta-blockers on blood pressure control and morbidity and mortality endpoints in hypertensives of African ancestry: an individual patient data meta-analysis

Introduction

Compared with first-line antihypertensives, beta-blockers (BB) have been reported to lower the central aortic blood pressure suboptimally and are associated with increased stroke risk. This observation has not been investigated in hypertensives of African ancestry. We hypothesised that an individual patient data meta-analysis (IPD-MA) on the efficacy of second- or third-generation beta-blockers (STGBBs) in hypertensives of African descent may provide new insights.

Methods

A single-stage IPD-MA analysed the efficacy of STGBB in lowering the mean arterial blood pressure and reducing the composite outcomes: cardiovascular death, stroke, and myocardial infarction.

Results

A total of 11,860 participants from four randomised control trials were included in the analysis. Second- or third-generation beta-blockers reduced the mean arterial pressure by 1.75 mmHg [95% confidence interval (CI):1.16-2.33; P < 0.001] in all participants included in the analysis, and by 1.93 mmHg (95% CI: 0.86-3.00; P < 0.001) in hypertensive Africans. In patients with established cardiovascular disease, where the benefits of BB therapy are well established, STGBBs were associated with an adjusted odds ratio of 1.33 (95% CI: 1.06-1.65; P = 0.015) of the composite outcome, most likely due to confounding. Similarly, the risk of total myocardial infarction was 1.76 times higher (95% CI: 1.15-2.68; P = 0.008) in hypertensives of African ancestry on STGBBs.

Conclusion

The STGBBs reduced the mean arterial pressure comparably to other antihypertensives, and they were not associated with an increased risk of stroke.

Propranolol-Associated Hypoglycemia in Patients on Maintenance Hemodialysis

Propranolol is widely employed in hemodialysis patients for the control of renin-dependent hypertension. Infrequent reports have linked hypoglycemia and propranolol, especially in complex situations such as malnutrition, anesthesia, and excessive insulin use. Three patients on maintenance hemodialysis taking propranolol developed severe hypoglycemia resulting in cardiac arrest. The life-threatening hypoglycemia occurred without apparent precipitating cause and unaccompanied by the classical signs and symptoms of hypoglycemia. These three cases suggest that propranolol in a setting of chronic renal failure and dialysis may bring about severe hypoglycemia, a complication previously unsuspected.

Compilation of Pharmacokinetic Parameters of Beta-Adrenergic Blocking Agents

After defining the drug class of β-adrenergic blocking agents, general aspects for clinical use of β-blockers are discussed, namely absorption, distribution, metabolism, elimination, correlation between clinical response and drug disposition, drug interactions, and influence of disease on drug response and disposition. Pharmacokinetic data for the following β-blockers were retrieved from the literature: acebutolol, alprenolol, atenolol, labetalol, metoprolol, nadolol oxprenolol, penbutolol, pindolol, practolol, propranolol sotalol, talinolol, timolol, and tolamalol. Those pharmacokinetic parameters which were not listed in the original literature were calculated. The use of pharmacokinetic parameters of β-blockers for clinical application is discussed.

The effects of a beta 1-blocking agent, atenolol, on blood pressure, plasma renin activity and prostaglandin F2 alpha excretion in patients with essential hypertension

The antihypertensive action of beta-blocking agents has been suggested to be associated with the decrease in plasma renin activity (PRA) and can be antagonized by indomethacin, a prostaglandin (PG) synthesis inhibitor. We studied the acute and long-term effects of a beta 1-blocking agent, atenolol (50 mg b.i.d.), on blood pressure (BP), PRA and urinary PGF2 alpha excretion in 12 male patients (40 years old) with essential hypertension. BP was measured by means of a brachial cuff. PRA and PGF2 alpha were estimated radioimmunologically. One day after the initiation of atenolol treatment, BP fell significantly, the supine values from 159/114 to 143/104 mmHg and the erect from 158/118 to 140/106 mmHg. In six weeks BP decreased further to 135/94 and 134/96 mmHg, respectively. After the cessation of atenolol for three weeks BP rose to the pre-atenolol level. When the dose was readjusted (25-150 mg daily for 26 weeks), diastolic BP remained at 100 mmHg or higher in only two patients. During the atenolol treatment PRA declined to one-third of the pre-atenolol level in one day and to one-half in six weeks. The urinary excretion of PGF2 alpha was not affected by atenolol. Our results suggest that 1) the antihypertensive action of atenolol and the reduction of PRA are substantial already in one day, and 2) the decrease in BP or PRA is not associated with PGF2 alpha production.

Anticonvulsant profile and mechanism of action of propranolol and its two enantiomers

The anticonvulsant properties of the ss-adrenoceptor antagonist propranolol and its two enantiomers were examined in various screening tests in order to characterize the anticonvulsant profile as well as the possible molecular mechanism of action. These compounds dose-dependently raised the threshold for tonic electroshock seizures in mice and were effective in the traditional maximal electroshock test (ED (50)s 15- 20 mg kg (-1)i.p.). In combination with clinically used antiepileptics, the anticonvulsant effectiveness of the latter was significantly increased. In the pentylenetetrazol (85 mg kg (-1)s.c.) seizure threshold test, ( +/-)- and ( +)-propranolol were not effective in preventing clonic seizures. In unrestrained rats with chronically implanted electrodes in the dorsal hippocampus, propranolol and its ( +)-enantiomer equieffectively reduced the duration of electrically-evoked hippocampal afterdischarges (10 and 20 mg kg (-1)i.p.) and raised the focal stimulation threshold (20 mg kg (-1)i.p.). In amygdala-kindled rats, both drugs ( >or= 10 mg kg (-1)i.p.) reduced the seizure severity from stage 5 (generalized clonic-tonic) to stage 3 (unilateral forelimb) seizures. Furthermore, whole-cell patch-clamp experiments showed that ( +)- as well as ( -)-propranolol ( 10(-6)to 10(-4)M) depressed the fast inward sodium current in a concentration- and use-dependent manner in cultured rat cardiomyocytes and inhibited picrotoxin-induced burst firing activity of mouse spinal cord neurones in culture. In conclusion, propranolol and its two enantiomers have anticonvulsant effects in models for generalized tonic-clonic and complex partial seizures which may be accounted for by the sodium channel blocking and not by the ss-adrenoceptor blocking activity.

Are sleep complaints an independent risk factor for myocardial infarction?

PURPOSE

To investigate whether subjective sleep complaints are an independent predictor of myocardial infarction (MI) in a community of older adults and to gain clues as to why the association between sleep complaints and incident MI exists.

METHODS

Using longitudinal data from the Piedmont study on 2960 adults aged 65 or older who were free of symptomatic heart disease at baseline, we screened 19 potential confounders to determine if any, alone or in combination, could explain the observed relationship between incident MI and sleep complaints.

RESULTS

During the three-year follow-up period, there were 152 incident MIs. Restless sleep (incidence density ratio (IDR) = 1.58, 95% confidence interval (CI) = 1.11, 2.24) and trouble falling asleep (IDR = 1.68, 95% CI = 1.09, 2.60) predicted incident MI after adjusting for age, gender, and race. IDRs were not substantially impacted by controlling for smoking, blood pressure, diabetes or obesity. After adjustment for education, number of prescription medicines, self-rated health, and depression score, all IDRs were nullified. In particular, self-rated health and depression were strong independent risk factors for MI.

CONCLUSIONS

A subjective sleep complaint increases the likelihood of a first MI in older adults without overt coronary heart disease (CHD) independently of classic coronary risk factors and appears to be a marker for a syndrome of depression and malaise that may have a causal relationship to MI.

Treatment with beta-adrenergic blocking agents after myocardial infarction: from randomized trials to clinical practice

OBJECTIVES

Our aim was to determine the percent of patients with myocardial infarction who are treated with beta-adrenergic blocking agents in dosages proved to be effective in preventing death after a heart attack.

BACKGROUND

In the prospective randomized trials showing that beta-blocker treatment improves survival rates after myocardial infarction, relatively high dosages of these agents were used. However, it is not known whether these dosages are used in current clinical practice.

METHODS

In a retrospective analysis of clinical data from 606 consecutive survivors of myocardial infarction at four university hospitals in three countries, we assessed the number of infarct survivors receiving prospectively defined "effective dosages" of beta-blockers. We defined these dosages as those that demonstrated improved survival rates of infarct survivors who received active drug in large, prospective, double-blind, placebo-controlled trials.

RESULTS

Only 58% of infarct survivors with no contraindications to beta-blockers received these drugs at the time of hospital discharge, and only 11% received dosages equivalent to > 50% of the effective dosages. Independent predictors of failure to prescribe beta-blockers to infarct survivors without contraindications to these drugs were the use of diuretic agents, transient heart failure, impaired left ventricular function and increased patient age. Among patients receiving beta-blockers, only the use of propranolol predicted prescription of a low beta-blocker dosage.

CONCLUSIONS

Failure to prescribe beta-blockers after myocardial infarction is common but in most cases is not due to clear contraindications. Many patients not receiving beta-blockers belong to subgroups that would derive the greatest benefit from such treatment. Finally, even when beta-blockers are prescribed, the dosages used are considerably lower than those proved to be effective in preventing death after myocardial infarction.

Around the beta-blockers, one more time

We review the pharmacology, pharmacokinetics, and relative costs of beta-blockers, as well as indications for and therapeutic controversies surrounding their use. It is hoped that this discussion will assist clinicians in making informed decisions when choosing a drug for a hospital formulary or a particular patient. Beta-blockers are indicated for a variety of noncardiovascular and cardiovascular conditions, including hypertension, ischemic heart disease, arrhythmias, and prophylaxis of myocardial infarction (MI). These agents compete with catecholamines at beta-adrenoreceptors. They have different ancillary properties, including intrinsic sympathomimetic activity (ISA), cardioselectivity, and membrane stabilizing-activity, and vary in their duration of action, route of elimination, and lipophilicity. Beta-blocking agents decrease oxygen demand by exerting a negative inotropic and chronotropic effect. They also reduce blood pressure and possess antiarrhythmic effects. Beta-blockers penetrate the central nervous system (CNS) to different degrees and can cause a wide variety of CNS adverse effects. Nonselective beta-blockers have been noted to slightly reduce renal blood flow. Nadolol is an exception in that either no change, or even a small increase in renal blood flow, is observed upon initiation of therapy. Beta-blockers also act on the pulmonary bed by preventing beta 2-mediated bronchodilation, thereby exacerbating bronchospastic disease in some patients. Beta-adrenergic blocking agents can potentiate both hypoglycemia and hyperglycemia in diabetic patients. Their effects on total peripheral resistance (TPR) are controversial. Initially it appears that beta-blockade increases TPR. After chronic therapy, however, TPR decreases to or below baseline values. These agents appear to be equally efficacious in the treatment of hypertension, arrhythmias, and ischemic heart disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Hormonal control of Mg2+ transport in the heart

Magnesium is abundant in the mammalian body and the second most abundant cation in cells. Because the concentration of intracellular free Mg2+ is relatively high (0.2-1 mM), Mg2+ is unlikely to act as a second messenger, like Ca2+, by rapidly changing its cytosolic concentration. But changes in Mg2+ do have profound effects on cellular metabolism, structure and bioenergetics. Key enzymes or metabolic pathways, mitochondrial ion transport, Ca2+ channel activities in the plasma membrane and intracellular organelles, ATP-requiring reactions, and structural properties of cells and nucleic acids are modified by changes in Mg2+ concentration. Yet, although some information is available from giant cells and bacteria, little is known about the regulation of intracellular Mg2+ in mammalian cells. Here we report a new transport mechanism for Mg2+ across the sarcolemma of cardiac cells in both intact hearts and dissociated myocytes. We show that noradrenaline, through beta-adrenergic stimulation and increase of cyclic AMP, stimulates a large efflux of Mg2+ from cardiac cells. This transport is of major dimensions and can move up to 20% of total cellular Mg2+ within a few minutes.

Hemodynamic effects of pindolol and atenolol at rest and during isometric exercise: a noninvasive study with healthy volunteers

Hemodynamic effects of intravenous and oral pindolol and atenolol were assessed in ten healthy volunteers by left ventricular echocardiography and systolic time intervals. Measurements were made at rest and during hand-grip-induced isometric exercise. Drug doses were pindolol 0.015 mg/kg intravenously and 10 mg/day orally, atenolol 0.1 mg/kg intravenously, and 50 mg/day orally. Heart rate at rest was reduced by both drugs. The reduction caused by atenolol during oral treatment was significantly greater (p less than 0.01). Intravenously only pindolol reduced mean arterial pressure. During oral treatment atenolol reduced the mean arterial pressure nonsignificantly. Both drugs lowered heart rate during isometric exercise, atenolol being significantly more effective. During oral treatment atenolol blunted the heart-rate reaction to exercise. Mean arterial pressure during isometric exercise rose slightly with both drugs after intravenous administration. During oral treatment only atenolol reduced the mean arterial pressure significantly. Intravenous atenolol reduced cardiac contractility at rest, indicated by significant decreases in fractional shortening, ejection fraction, and the mean velocity of circumferential fiber shortening. In contrast, intravenous pindolol and oral therapy with either drug did not change contractility. Intravenous atenolol raised total peripheral resistance. The preejection period/left ventricular ejection time ratio decreased with intravenous pindolol, while atenolol increased it. In conclusion, atenolol had more negative inotropic and chronotropic effects, especially after acute intravenous administration. Only atenolol reduced cardiac output and increased peripheral resistance. After repeated oral administration, these effects were less apparent.(ABSTRACT TRUNCATED AT 250 WORDS)

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).

Beta-adrenergic blockers

beta-Adrenergic blocking drugs have been available for several years to treat ischemic heart disease and other cardiovascular and noncardiovascular disorders. There are multiple drugs in this class with various pharmacodynamic and pharmacokinetic properties that may be important in specific clinical situations and in avoiding certain adverse reactions. These drugs have been shown to be efficacious in relieving anginal symptoms and prolonging exercise tolerance, in reducing high blood pressure, for treating various arrhythmias, in therapy of hypertrophic cardiomyopathy, and for prolonging life in many survivors of acute myocardial infarction.

Bevantolol. A preliminary review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy in hypertension and angina pectoris

Bevantolol is a new beta-adrenoceptor antagonist which possesses a relatively high degree of selectivity for beta 1-adrenoceptors. It is devoid of intrinsic sympathomimetic activity and possesses only weak local anaesthetic properties. Interestingly, bevantolol has been shown to cause a lowering effect on peripheral vascular resistance. Available clinical data indicate that bevantolol, given once or twice daily, is an effective agent in the management of mild to moderate hypertension and stable angina pectoris. In hypertension bevantolol has been shown to be of comparable therapeutic efficacy to both atenolol and propranolol, while in patients with angina pectoris the drug compared favourably with atenolol. During short and long term administration bevantolol has been well tolerated and few patients have withdrawn from treatment because of adverse effects. However, although the properties of bevantolol may offer theoretical advantages in some patients, only a few comparative studies have been reported, and thus it is presently unclear what advantages bevantolol may offer over existing treatments for hypertension or angina pectoris.

Disturbances of sleep and wakefulness associated with the use of antihypertensive agents

Sleep disturbances are frequently associated with the use of antihypertensive drugs. They are observed mainly during the administration of drugs that affect central adrenergic mechanisms. Beta-adrenoceptor antagonists which readily penetrate into the brain (propranolol, pindolol) increase wakefulness and/or decrease REM sleep. Alpha 2-adrenoceptor agonists (clonidine, guanfacine) markedly reduce the duration of REM sleep. The catecholamine depleting agent reserpine increases REM sleep during single or repeated-dose administration, while the MAOI phenelzine shows opposite effects. The 5-HT2 antagonist ritanserin, which is chemically related to the antihypertensive agent ketanserin, increases slow wave sleep while REM sleep is decreased. Sleep disturbances have not been reported during the administration of calcium entry antagonists. However, they seem to modify the effects of hypnotics and CNS stimulants. There are no formal studies on the effects of angiotensin converting enzyme inhibitors and vasodilators on sleep in man.

Clinical differences between beta-adrenergic blocking agents: implications for therapeutic substitution

The beta blockers exhibit clinically significant differences in beta-receptor selectivity, intrinsic sympathomimetic activity, and alpha-adrenergic blocking activity. These agents also show important differences in their pharmacokinetic profiles, including gastrointestinal absorption, first-pass hepatic metabolism, lipid solubility, protein binding, hepatic biotransformation, pharmacologic activity of metabolites, and renal clearance of unchanged drug and metabolites. These many differences determine the appropriateness of administering a given beta blocker in a given clinical situation. The selection of beta blockers must also take into account concurrent therapy with other agents. Concurrent administration of beta blockers with drugs that alter gastric, hepatic, or renal function may affect blood levels, duration of action, or efficacy of beta-blocker action. The beta blockers vary in the extent to which their action is altered when they are given with other agents, and therapeutic substitution may produce unwanted side effects and toxicity. Elderly patients should be carefully monitored following interchange among beta blockers, since the probability of drug interaction, impact of adverse effects, unpredictability of response, and physiologic variability of renal and liver function is greater than for younger individuals. Therapeutic substitution among beta blockers in patients already stabilized on a given agent will require careful monitoring. Retitration with the new beta blocker will be required in many cases to assure therapeutic equivalence. Beta blockers are currently used for over 20 medical conditions. There is wide variation in the strength of the clinical evidence supporting the use and efficacy of specific beta blockers for specific conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Treatment of hypertension. Patterns of drug utilization in a metropolitan population

In the Munich Blood Pressure Study (MBS), a cross-sectional study (MBS I) with follow-up (MBS II) of a random sample of 3,198 citizens aged 30-69 (response rate, 69.3%), treatment and control of hypertension were examined. Of the actual hypertensives 59% (221) in MBS II (373) were on drug treatment and about two-thirds (150) of those being treated had controlled blood pressure (BP). Women's BP was better controlled than men's. Of the 221 treated hypertensives 85% (188) received types of drugs or drug combinations which were in accordance with the recommendations of the German Hypertension League. However, this did not apply to the prescribed dosages of the various drugs. Of the treated hypertensives 52% were either on a diuretic, on a beta-blocker, or on a combination of both drugs. Rauwolfia alkaloids combined with a diuretic were given to 27%. In 79% of the participants who had received a beta-blocker either alone or in combination with other antihypertensive agents and who still had high BP values, the prescribed beta-blocker dosage was below the recommended daily dose. Fatigue was the most frequently reported symptom, possibly attributable to antihypertensive drug treatment. Electrocardiographic signs of left ventricular hypertrophy were found less frequently in controlled hypertensives, in comparison to treated but uncontrolled hypertensives or untreated hypertensives.

Presynaptic beta-adrenoceptors

The existence of facilitatory presynaptic beta-adrenoceptors has been shown in approximately 30 tissues of 6 different species including human. A positive feed back loop for further release of the transmitter appears to be activated by an endogenous agonist, epinephrine, taken up and released as a cotransmitter with norepinephrine rather than norepinephrine itself released from peripheral noradrenergic nerve terminals. Presynaptic beta-adrenoceptors are mainly of a beta 2-subtype. Some beta 1-subtype receptors are also suggested. There coexist presynaptic beta 1- and beta 2-adrenoceptors in cat and rat hypothalamus. Higher sensitivity of peripheral presynaptic beta-adrenoceptors to isoproterenol may be implicated in the early development of hypertension in SHR. Epinephrine taken up and released initiates the development of hypertension in rats via activation of these receptors. Increased activation of these receptors by epinephrine may play a role in the development of essential hypertension. The antihypertensive action of beta-antagonists may be in part due to blockade of these facilitatory presynaptic beta-adrenoceptors.

Distribution of beta-adrenoceptor blocking drugs into cerebrospinal fluid in rats

The distribution into cerebrospinal fluid (CSF) of five 3H- or 14C-labelled beta-adrenoceptor blocking drugs given intravenously was studied in urethane-anaesthetized rats. The doses (mg/kg) were: alprenolol 5, metoprolol 1, oxprenolol 5, pindolol 0.5, propranolol 0.1 and 5. Within 15 min. a marked fraction of the given radioactivity appeared in CSF with all substances. During the follow-up period of 315 min., only propranolol, independently of dose, caused high CSF/plasma ratios (0.54-0.73) of radioactivity. The other four beta-adrenoceptor blocking drugs caused levels of CSF radioactivity which were 0.05-0.28 of that in plasma and 0.05-0.14 of the calculated levels of activity in the whole body. Since propranolol is bound to plasma proteins to a higher degree than the other drugs studied, the penetration of the unbound fraction of propranolol into rat CSF is even more pronounced than what would be expected on the basis of CSF/plasma ratio measured.

Ancillary pharmacologic properties of acebutolol: cardioselectivity, partial agonist activity, and membrane-stabilizing activity

Acebutolol, a new beta-blocking agent, possesses the ancillary pharmacologic properties of cardioselectivity and partial agonist and membrane-stabilizing activities. Compared to propranolol at equipotent doses, acebutolol produces less bronchoconstriction and preserves the bronchodilator response to isoprenaline. Similarly, acebutolol has less of an effect on peripheral vascular hemodynamics than does propranolol. Because of partial agonist activity, acebutolol produces a lesser reduction in heart rate and cardiac output than do propranolol and atenolol and has been found to have minimal effects on lipoprotein metabolism. Acebutolol may be the only beta-blocking agent that demonstrates some membrane-stabilizing activity at clinically achievable plasma concentrations. The ancillary pharmacologic properties of cardioselectivity and partial agonist activity are distinct and offer definite advantages to selected patients, particularly patients with respiratory disease, in whom cardioselective acebutolol, particularly at low doses, can minimize patient risk. The ancillary property of membrane-stabilizing activity may also guide therapy in selected patients.

Effects of atenolol, labetalol and propranolol on the peripheral circulation in hypertensive patients without obstructive vascular disease

In an observer-blind, randomised cross-over trial, in 12 patients, the effects on the peripheral circulation of antihypertensive doses of atenolol, labetalol and propranolol and placebo were compared. After a placebo period of at least 4 weeks, patients were allocated at random to one of the three active drug treatments. After active treatment for at least 6 weeks and a fall in diastolic pressure (DP) to less than 90 mmHg subjects were switched to the next medication. At the end of each period, photo-electric plethysmography (PHELP) was done on all fingers of one hand cooled over 4 min in water in steps of 3 degrees C from 33 degrees to 12 degrees C, and subsequently warmed in room air (20 degrees C) for a period of 10 min. Blood flow changes during cooling were expressed as a percentage of the initial PHELP value (% PHELP). Areas under the curves, representing the % PHELP/cooling period and % PHELP/warming-up period, showed that within the temperature range normally encountered in daily life, labetalol preserved finger blood flow significantly better than propranolol and marginally better than placebo. With atenolol, finger blood flow was not significantly different from that during the three other regimens, but there were significantly fewer other side-effects. It is concluded that labetalol may be the drug of choice for hypertensive patients treated with beta-blocking agents whose peripheral arterial circulation seems inadequate at low temperatures.

Brain levels and acute antihypertensive activity of beta-blockers

The penetration of beta-adrenoceptor blockers into the cerebrospinal fluid and into brain tissue is related to the lipophilicity of these drugs, as reflected by the partition coefficients between octanol and aqueous buffers. However, experimental techniques in animal models show no obvious relationships between the degree of brain penetration and the acute central antihypertensive effect of certain beta-blockers. This discrepancy is demonstrated convincingly by comparative experiments with atenolol and metoprolol. Both drugs are beta 1-selective blockers, and atenolol is highly polar, whereas metoprolol is lipophilic. Both these beta-blockers penetrate the CNS but to differing degrees. The experiments performed with these compounds support other studies described in the literature and do not suggest that there is a central mechanism which underlies the antihypertensive activity of beta-blockers.

The lowering of daytime blood pressures with a single daily dose of acebutolol in ambulant hypertensives

Intra-arterial blood pressure recordings were studied in 10 ambulant subjects with essential hypertension to evaluate the effect of a single daily dose of acebutolol. Blood pressures and heart rates, measured on a beat-to-beat basis were averaged over every hour, for the daytime, night-time, and for the total 24 hours. Acebutolol significantly lowered the average daytime systolic pressure (160 to 142 mmHg, p = less than 0.01), diastolic pressure (78 to 66 mmHg, p = less than 0.01), and the heart rate (92 to 77 beats/min, p = less than 0.001). Significantly lower pressures were demonstrated up to 11 hours after the last dose of acebutolol. The effect on heart rate lasted up to 13 hours. The observed lowering of pressures and heart rate during the remaining 11 hours did not reach statistical significance.

Nadolol compared to propranolol for treating chronic stable angina pectoris

In order to determine the relative efficacy and dose equivalency of propranolol four times a day and nadolol once daily for the treatment of stable angina pectoris, ten patients were studied in a double blind randomized placebo controlled crossover study. Total daily doses of propranolol and nadolol were determined by titrating until an equivalent degree of reduction in the heart rate response to exercise was achieved. At these doses, the treadmill exercise time to 0.1 mV of electrocardiographic ST-segment depression was increased from 248 +/- 75 seconds on placebo to 405 +/- 56 seconds on propranolol (p less than 0.05) and 471 +/- 46 seconds on nadolol (p less than 0.01). Also, the mean frequency of angina decreased from eight attacks per week on placebo to three on propranolol and nadolol (both p less than 0.05). In six of the ten patients, the effective total daily dose of propranolol and nadolol was identical, and the dose ratio for all ten patients was 1.17:1, propranolol to nadolol. However, individual dose titration is recommended when switching from propranolol four times a day to nadolol once daily because of the dosage variability noted in 40 percent of the patients.

Beta blockers in hypertension

Beta-adrenoceptor antagonists are effective in the management of patients with mild-to-moderate hypertension. Noncardioselective agents, cardioselective agents and beta blockers with intrinsic sympathomimetic activity (ISA) are equally effective, provided they are used in equipotent doses. Beta blockers can be used as first-line therapy in the management of hypertension and can be safely combined with diuretics, vasodilators, or both, for a better control of blood pressure. The exact mechanism by which beta blockers decrease blood pressure remains speculative, but they all reduce cardiac output during long-term therapy; drugs with ISA lower cardiac output and heart rate less than do drugs without ISA. Pharmacokinetic properties of beta blockers differ widely; drugs metabolized by the liver have shorter plasma half-lives than drugs primarily excreted by the kidneys. Although many of the side effects of various beta blockers are similar, differences in water and lipid solubility account for a higher incidence of central nervous system side effects with lipid-soluble drugs (such as propranolol and metoprolol) than with hydrophilic drugs (such as atenolol and timolol). The incidence of cold extremities has been reported to be less with drugs with ISA, and the incidence of bronchospasm less with cardioselective drugs. In the management of uncomplicated mild-to-moderate hypertension, all beta blockers are equally effective and produce less troublesome side effects than alternative antihypertensive agents. For effective therapy beta blockers can be used in 2 divided daily doses or even once daily.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Transient in oxygen uptake after step-increase of workload under beta-adrenoceptor blockade or vasodilation

The effect of vasodilation (with nifedipine) or beta-adrenergic receptor blockade (with propranolol, alprenolol or metoprolol) on the rate of rise of oxygen uptake and heart rate were studied in 14 healthy subjects after a step-wise increase of workload from a light to a moderate exercise intensity. Under beta-adrenergic receptor blockade steady state oxygen uptake at both workload levels was equal to control values; heart rate went up to 111 min-1 (s.d.:15) vs 150 min-1 (s.d.:24) for the control experiments. The half-times of the oxygen uptake transient were unchanged. After vasodilation with nifedipine heart rates were higher (20% for the lower and 12% for the higher exercise level) but steady state oxygen uptake levels and rate of rise were also unchanged. It is concluded that the rate of rise of oxygen supply to working skeletal muscles after a stepwise increase of load is not reduced either by a beta-adrenergic receptor blocking drug nor by a vasodilating agent. Discomfort during exercise appears to be a subjective phenomenon related to reduced skin circulation and sweating under beta-adrenergic receptor blockade, or to headache and congestion after vasodilatory drug administration. These side-effects are not caused by a reduced oxygen supply of muscle, neither under steady state situations nor under rapid changing workload conditions.

Clinical pharmacokinetics of cerebrospinal fluid

The distribution of drugs into the cerebrospinal fluid has long been considered a challenging field of investigation in 2 major respects: (a) understanding how the physicochemical properties (molecular weight, pKa, plasma protein binding) of various molecules influence their movements across such a specific structure as the blood-brain barrier; and (b) defining the relationship between cerebrospinal fluid concentrations of various drugs and their central (side) effects. An attempt has been made to review the very dispersed information presently available to offer a clinically orientated picture of this area of pharmacokinetics. Drugs acting on the central nervous system (benzodiazepines, tricyclic antidepressants, anticonvulsants, opioids), antibacterial agents, cardiovascular drugs (beta-adrenoceptor blockers and digoxin), antineoplastic drugs (mainly methotrexate), and other miscellaneous agents (corticosteroids, cimetidine, methylxanthines) are reviewed. The available evidence seems to support the conclusion that only for methotrexate and antibacterial agents does knowledge of cerebrospinal fluid pharmacokinetics have direct therapeutic implications, while the mosaic of information available for other drugs does little more than provide a partially satisfactory picture.

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

Pindolol is a new noncardioselective beta adrenergic blocking agent with intrinsic sympathomimetic activity. In the treatment of mild to moderate hypertension, pindolol provides effective control of blood pressure in a large majority of patients when administered alone or, more commonly, when combined with a thiazide diuretic. Pindolol is approximately as effective as propranolol in the therapy of hypertension, but in some crossover trials central nervous system side effects were more frequent with pindolol. A "ceiling effect" may be observed as dosages are titrated upward above approximately 20 to 30 mg per day, such that further blood pressure reductions may not be achievable. Some patients will exhibit a paradoxical increase in blood pressure with an increase in dosage. In patients who respond to modest doses of pindolol, twice or even once daily dosing is often adequate. This prolonged duration of hypotensive activity, while not suggested by the kinetics of this or similar drugs, is probably common to most beta blockers. Investigations in small numbers of patients with angina pectoris have reported variable but generally beneficial results with pindolol.

Influence of beta-adrenoceptor blocking agents on lymphocyte function in vitro

1 In order to assess whether beta-adrenoceptor blocking agents may have an immunomodulatory influence, the in vitro effect of propranolol metoprolol and atenolol on mitogenic activation of human peripheral blood lymphocytes was studied. To investigate further the mechanism of this influence, the effects of quinidine and two other membrane stabilizing agents were examined. 2 At 100 and 1000 mumol/l, both (+)-propranolol, (-)-propranolol and (+/-)-propranolol evoked a strong reduction of mitogenic lymphocyte activation. A similar effect was obtained with quinidine. Even at 1000 mumol/l metoprolol, had only a slight suppressive effect and atenolol had no suppressive influence at all. 3 It appears that propranolol may suppress mitogenic activation of lymphocytes, and that the effect may be ascribed to membrane stabilization rather than to beta-adrenoceptor blockade.

Dose response of oral timolol combined with adrenaline

Oral timolol, a beta-adrenergic receptor blocker, was given in 5 different doses from 5 mg to 30 mg a day to 12 healthy volunteers in a double-blind cross-over trial. Adrenaline was instilled into one eye in each subject. Recording of intraocular pressure during the trial suggested the presence of a dose-response relationship between the dose of timolol and the decrease of intraocular pressure. An analysis of the interaction of timolol and adrenaline showed that the adrenaline effect diminished linearly with increasing timolol dose, which finally made the combination less effective than timolol alone.

Additive intraocular pressure reducing effect of topical timolol during systemic beta-blockade

The effect on intraocular pressure (IOP) of topical timolol was studied in 30 patients with arterial hypertension treated with oral alprenolol, metoprolol or timolol. No patient had any known eye disorder. Topical administration of timolol induced a significant reduction of IOP regardless if the patients had systemic beta-blockade or not. Treatment with topical timolol alone was equally effective in reducing IOP as combined topical and oral therapy. Patient compliance was checked with plasma concentrations of the different beta-blockers.

Beta-adrenoceptor blockade and atrio-ventricular conduction in dogs. Role of intrinsic sympathomimetic activity

1 Atrio-ventricular conduction and its modifications induced by six beta-adrenoceptor blocking agents and isoprenaline have been investigated in the anaesthetized dog using the extrastimulus technique and measuring atrial (AERP), nodal (NERP), global (GERP) effective refractory periods as well as global functional refractory period (GFRP). 2 When beta-adrenoceptor blockade was produced by (+/-)-propranolol (beta 1 + beta 2-adrenoceptor blockade) which is devoid of intrinsic sympathomimetic activity (ISA) but has membrane stabilizing effects (MSE), sotalol (beta 1 + beta 2-adrenoceptor blockade, no ISA, no MSE) and atenolol (beta 1-adrenoceptor blockade, no ISA, no MSE), all parameters were significantly increased. When beta-adrenoceptor blockade was achieved with pindolol (beta 1 + beta 2-adrenoceptor blockade) and practolol (beta 1-adrenoceptor blockade) which have ISA but no MSE, all parameters remained unchanged, as was also the case with (+)-propranolol, which has MSE but neither ISA nor beta-adrenolytic properties. 3 Isoprenaline at high doses significantly reduced the refractory periods but when infusion was stopped, marked but reversible conduction depression was observed. 4 It thus appears that beta-adrenoceptor blockade but not MSE is responsible for the onset of atrial and AV-conduction impairment and that ISA affords protection against this impairment.

Pharmacokinetics, mechanisms of action, indications, and adverse effects of timolol maleate, a nonselective beta-adrenoreceptor blocking agent

Timolol, a nonselective beta-adrenoreceptor blocking agent without intrinsic sympathomimetic or membrane stabilizing activity, has been shown effective in the treatment of angina and hypertension. It is particularly useful in patients with stable angina pectoris and patients with mild to moderate hypertension. In both of these conditions, timolol appears to be comparable to propranolol. A recent study has suggested that timolol reduces mortality and reinfarction rate in patients who have recently had a myocardial infarction. When given topically timolol reduces intraocular pressure in patients with open-angle glaucoma; the drug may be used as the primary agent or as an adjunct to standard therapy. Careful selection of patients will reduce the frequency of adverse effects due to beta-receptor inhibition. Thus, timolol should not be used in patients who are predisposed to asthmatic bronchitis or cardiac failure, and it should be used with caution in patients with peripheral vascular disease or diabetes mellitus.

Comparative studies of (--)-, (+/-)-propranolol, atenolol, guanethidine, bretylium and tetracaine on adrenergic transmission

1 Effects of (--)-, (+/-)-, and (+)-propranolol, atenolol, guanethidine, bretylium and tetracaine were studied on relaxation responses of rabbit ileum and contractile responses of rabbit pulmonary artery and guinea-pig vas deferens to electrical nerve stimulation (2 to 50 Hz). 2 In the ileum, inhibition by tetracaine 3.3 x 10(-6) M occurred at high frequencies of stimulation, while bretylium 1.2 x 10(-4) M and guanethidine 2 x 10(-5) M inhibited responses at all frequencies, the latter producing greater inhibition at low frequencies. 3 (+/-)-Propranolol 10(-5) M produced a tetracaine-type inhibition after 1 h and a bretylium-pattern after 2 h in the ilea and pulmonary arteries and a transition from bretylium- to guanethidine-pattern in the vas deferens, while atenolol 2 x 10(-5) to 10(-4) M produced guanethidine-type inhibition in all preparations. 4 (--)-, (+/-)-, and (+)-Propranolol 3 x 10(-6) to 3.3 x 10(-5) M were equipotent in the vas deferens and ileum. However, inhibition by (--)-propranolol 3.3 x 10(-5) M persisted in the ileum, while that by the (+)-isomer was partially restored by washing. 5 (--)- or (+)-Propranolol 3.3 x 10(-5) M or atenolol 2 x 10(-5) M did not inhibit relaxation of the ileum after the bath temperature was maintained at 4 degrees C for 2 h during drug application. 6 In conclusion, propranolol and atenolol both have gradually developing guanethidine-like adrenergic neurone blocking actions.

Changes in ischemic blood flow distribution and dynamic severity of a coronary stenosis induced by beta blockade in the canine heart

The effects of equipotent beta 1-receptor-blocking doses of propranolol, metoprolol and sotalol on distal coronary pressure, stenosis resistance and regional myocardial blood flow (endo/epi) were studied in anesthetized dogs with a severe noncircumferential stenosis of the left circumflex coronary artery. No significant differences between the three beta blockers were observed for overall hemodynamics and regional myocardial blood flow. After drug treatment, subendocardial blood flow (0.47 +/- 0.05 to 0.78 +/- 0.05 ml/min/g) and endo/epi (0.67 +/-0.04 to 1.18 +/- 0.04) increased significantly (p less than 0.05) in the ischemic region. These changes were associated with a marked increase in distal coronary perfusion pressure and a decrease in heart rate. Resistance across the stenosis decreased significantly (p less than 0.05) after beta-receptor blockade (3.2 +/- 0.3 to 1.4 +/- 0.2 units). Atrial pacing to control heart rate only partially attenuated these changes. These results suggest that a favorable redistribution of ischemic blood flow after beta blockade is the result of an increase in distal diastolic pressure-time index and an autoregulation-induced increase in distal bed vascular resistance due to a decrease in myocardial oxygen demand associated with beta blockade. The latter effect also resulted in a decrease in the dynamic severity of a proximal coronary stenosis.

Influence of intrinsic sympathomimetic activity of beta-adrenoceptor blockers on the heart rate and blood pressure responses to graded exercise

1 The relationship between plasma concentration and effect on heart rate and blood pressure at rest and at three levels of exercise were examined for four β-adrenoceptor blocking drugs having differing pharmacological properties.

2 Four doses of each drug were administered, the highest doses producing maximum effects of the work-heart rate and work-blood pressure relationships.

3 Pindolol and oxprenolol, which have intrinsic sympathomimetic activity (ISA) differed from timolol and metoprolol (which do not) in having a smaller effect on resting heart rate at each dose.

4 During exercise the four drugs had similar maximum effects on slope of the work-heart rate relationship suggesting similar suppression of reflex enhancement of sympathetic activity during exercise by each drug. The higher heart rate after drugs with ISA at rest was therefore still present at each level of exercise, e.g. maximum reduction of heart rate at 0.5 maximum work capacity was 20.5, 20.8. 24 and 28% for pindolol, oxprenolol, metoprolol and timolol respectively (P < 0.01 for difference between drugs with and without ISA).

5 The relationship between plasma concentration and reduction of heart rate at 0.5 maximum work capacity was qualitatively similar for each drug and was adequately described by a sigmoidal relationship wtih half-maximal effects at 4.4, 22, 35 and 5 ng/ml for pindolol, oxprenolol, metoprolol and timolol respectively whilst maximal effects occurred at approximately 30, 150, 100 and 30 ng/ml.

6 The results suggest that differences with exercise heart rate due to ISA are mainly due to effects on resting heart rate. The dose-response relationship of β-adrenoceptor blockers reaches a plateau at higher doses, irrespective of whether or not they possess ISA.