Ambulatory blood pressure during once-daily randomised double-blind administration of atenolol, metoprolol, pindolol, and slow-release propranolol

Sleep-Disordered Breathing in Heart Failure - A Therapeutic Dilemma

Sleep-disordered breathing (SDB) occurs in approximately 50% of patients with reduced left ventricular ejection fraction receiving contemporary heart failure (HF) therapies. Obstructive (OSA) and central sleep apneas (CSA) interrupt breathing by different mechanisms but impose qualitatively similar autonomic, chemical, mechanical, and inflammatory burdens on the heart and circulation. Because contemporary evidence-based drug and device HF therapies have little or no mitigating effect on the acute or long-term consequences of such stimuli, there is a sound mechanistic rationale for targeting SDB to reduce cardiovascular event rates and prolong life. However, the promise of observational studies and randomized trials of small size and duration describing a beneficial effect of treating SDB in HF via positive airway pressure was not realized in 2 recent randomized outcome-driven trials: SAVE, which evaluated the cardiovascular effect of treating OSA in a cohort without HF, and SERVE-HF, which reported the results of a strategy of random allocation of minute-ventilation-triggered adaptive servo-ventilation (ASV) for HF patients with CSA. Whether effective treatment of either OSA or CSA improves the HF trajectory by reducing cardiovascular morbidity or mortality has yet to be definitively established. ADVENT-HF, designed to determine the effect of treating both CSA and non-sleepy OSA HF patients with a peak-airflow triggered ASV algorithm, could resolve this present clinical equipoise concerning the treatment of SDB.

Benefits of once-daily therapies in the treatment of hypertension

In patients with hypertension, 24-hour blood pressure control is the major therapeutic goal. The number of daily doses is one characteristic of an antihypertensive agent that may affect the adequacy of 24-hour control. One measure of therapeutic coverage is the 24-hour trough-to-peak ratio, which determines the suitability of an agent for once-daily administration. The closer an agent is to a 100% trough-to-peak ratio, the more uniform the 24-hour coverage and therefore blood pressure control. High trough-to-peak ratio, long-acting antihypertensive medications lower blood pressure more gradually, which reduces the likelihood of adverse events attributable to abrupt drug action that occurs with shorter-acting agents. In hypertension, the natural diurnal variation of blood pressure may be altered, including elevated nighttime pressures. An optimal once-daily hypertension therapy would not only lower blood pressure but also normalize any blunted circadian variations in blood pressure. The benefits of once-daily agents with sustained therapeutic coverage may also be explained, in part, by increased patient adherence to simpler regimens as well as lower loss of blood pressure control during virtually inevitable intermittent noncompliance. Studies have demonstrated that once-daily antihypertensive agents have the highest adherence compared with twice-daily or multiple daily doses, including greater adherence to the prescribed timing of doses.

Twenty-four-hour ambulatory blood pressure measurement in clinical practice and research: a critical review of a technique in need of implementation

This review presents evidence that ambulatory blood pressure measurement (ABPM) should be used more widely in clinical practice and hypertension research. The technique, which should be mandatory in trials of antihypertensive drugs, is not being used in all studies of antihypertensive drug efficacy. ABPM is also being under-used in outcome studies. The failure to implement ABPM in primary care and hypertension research is impeding patient management and scientific advancement. ABPM offers so many advantages in assessing the efficacy of blood pressure (BP)-lowering drugs that it should be mandatory in pharmacological trials. Likewise, the technique provides a means of achieving BP control in clinical practice, which is essential if we are to halt the epidemic of the cardiovascular consequences of hypertension. However, if ABPM is to be implemented for these purposes, certain requirements will need to be fulfilled. These include the availability of accurate, patient-friendly and inexpensive devices; standardization of the presentation and plotting of data with summary statistics for day-to-day practice; provision of comprehensive data analysis for research; an interpretative report to facilitate use in busy clinical practice; a trend report to demonstrate efficacy or otherwise of treatment in clinical practice and online transmission of data to provide immediate real-time data analysis. The reasons why ABPM is not being implemented are reviewed, and proposals are made to make the technique more acceptable.

A comparison of 100 mg atenolol and 100 mg metoprolol once a day at rest and during exercise in hypertensives

The effects of once daily dosage of the two cardioselective beta-adrenoceptor blocking agents, atenolol and metoprolol, were studied in 26 patients with primary hypertension. The study was a randomized double-blind cross-over trial with placebo run-in and wash-out. Assessment of effect was performed about 1 and 25 hours after dosing. At rest, both atenolol and metoprolol lowered the blood pressure (BP) and heart rate (HR) compared to placebo. Atenolol induced a more effective BP reduction than metoprolol, especially 25 hours after drug intake. During exercise 1 hour after dosing both drugs reduced BP and HR to a similar extent, whereas 25 hours after dosing atenolol gave a more efficient BP and HR reduction than metoprolol. Our data show that both 100 mg atenolol and 100 mg metoprolol are effective antihypertensive beta-blockers at rest and during exercise, 1 hour after intake. Metoprolol was less effective than atenolol 25 hours after dosing probably due to its shorter plasma half-life, thus implying a twice daily regimen for metoprolol in standard preparation.

Influence of time and physical activity on blood pressure and heart rate during treatment with beta-blocking agents once daily

In a cross-over study of 52 middle-aged patients with mild to moderate essential hypertension, we have compared the effect and tolerability of 100 mg atenolol and 100 mg metoprolol given once daily. After 1 1/2 and 3 months of treatment, both systolic and diastolic blood pressure 24 hours after drug intake were significantly lower on atenolol. There were no significant differences after 3 months when blood pressure was read 3-4 hours after dose intake. During exercise, systolic blood pressure and heart rate were--at all work-loads--significantly lower on atenolol. Four patients on metoprolol and one patient on atenolol discontinued treatment owing to side-effects. The results support the need for thorough analysis of the duration of action and influence of physical activity and sympathetic tone in comparisons between presumedly equivalent antihypertensive drugs.

A comparison of the trough-to-peak ratio of cardio-selective beta-blockers in patients with newly diagnosed hypertension

INTRODUCTION

The drug can be administered once a day, if the trough-to-peak ratio (T/P) exceeds 50-66%. The objective of this work was to determine and compare the T/P ratio for betaxolol hydrochloride and for extended-release metoprolol tartrate.

METHODS

An open, randomized, prospective, comparative clinical study. The 24-h ambulatory blood pressure was measured with a SpaceLab 90207 automatic instrument (Redmond, Washington, USA) before and after 3 months of beta-blocker treatment. In order to determine the peak value, the individual maximum hourly mean blood pressure reduction was determined in the 3 to 6-h post-dose interval. For the determination of the trough value, the individual hourly mean blood pressure decrease in the 23-h post-dose interval, minimal 30 min after getting up in the morning was used. The T/P ratio was calculated as the mean of individual T/P ratios with statistical description of standard deviation (SD) and 95% confidence intervals (CIs).

RESULTS

Betaxolol hydrochloride reduced the mean peak systolic blood pressure value by 17.87+/-8.32 mmHg, the mean peak diastolic blood pressure value by 16.07+/-6.65 mmHg, the mean trough systolic blood pressure value by 11.83+/-5.98 mmHg and the mean trough diastolic blood pressure value by 11.33+/-6.74 mmHg. The mean T/P ratio was calculated as 72.84+/-33.32% (95% CI, 60.40-85.285%) for systolic blood pressure and as 71.57+/-29.35% (95% CI, 60.62-82.53%) for diastolic blood pressure. Metoprolol reduced the mean peak systolic blood pressure value by 16.70+/-10.54 mmHg, the mean peak diastolic blood pressure value by 14.20+/-8.67 mmHg, the mean trough systolic blood pressure value by 11.30+/-9.12 mmHg and the mean trough diastolic blood pressure value by 10.00+/-8.38 mmHg. The mean T/P ratio was calculated as 70.59+/-31.66% (95% CI, 58.76-82.41%) for systolic blood pressure and as 66.95+/-31.60% (95% CI, 55.15-78.75%) for diastolic blood pressure.

CONCLUSION

The T/P ratio determined for betaxolol hydrochloride and extended-release metoprolol tartrate is higher than 66%. This ratio guarantees a satisfactory 24-h effect of both the above-mentioned drugs.

Comparative in vivo evaluation of propranolol hydrochloride after oral and transdermal administration in rabbits

The purpose of this study was the in vivo evaluation of orally and transdermally administered propranolol hydrochloride in rabbits. Transdermal patches of propranolol hydrochloride (PPN) were formulated employing ethyl cellulose and polyvinylpyrrolidone as film formers. The pharmacodynamic (PD) and pharmacokinetic (PK) performance of PPN following transdermal administration was compared with that of oral administration. This study was carried out in a randomized cross-over design in male New Zealand albino rabbits. The PK parameters such as maximum plasma concentration (C(max)), time for peak plasma concentration (t(max)), mean residence time (MRT) and area under the curve (AUC(0-alpha)) were significantly (P<0.01) different following transdermal administration compared to oral administration. The terminal elimination half-life (t(1/2)) of transdermally delivered PPN was found to be similar to that following oral administration. In contrast to oral delivery, a sustained therapeutic activity was observed over a period of 24 h after transdermal administration compared to oral administration. The relative bioavailability of PPN was increased about fivefold to sixfold after transdermal administration as compared to oral delivery. This may be due to the avoidance of first pass effect of PPN. The sustained therapeutic activity was due to the controlled release of drug into systemic circulation following transdermal administration.

Relationship between calcium channel antagonists and nocturnal hypotension and autonomic imbalance in patients with a previous myocardial infarction

The present study was conducted to evaluate the effect of calcium channel antagonists on diurnal changes in blood pressure and on autonomic function in 71 patients who were receiving a calcium channel antagonist because they had previously suffered a myocardial infarction. Ambulatory blood pressures and Holter ECGs were recorded simultaneously for 24 h. Autonomic function was assessed by heart rate variability. Nocturnal systolic pressure was > or = 90 mmHg in 63 patients (group I) and < 90 mmHg in 8 patients (group II). Significant day to night changes in high-frequency power (from 4.3 +/- 1.2 to 4.5 +/- 1.0/m2) as well as in the ratio of low-frequency power to high-frequency power (from 1.3 +/- 0.1 to 1.1 +/- 0.2) were observed in group I. whereas such changes were blunted in group II. When the calcium antagonist was discontinued or the dose was reduced in group II, the autonomic imbalance improved along with elevation of nocturnal systolic blood pressure. Thus, nocturnal blood pressure should be monitored when such drugs are administered for the treatment of ischemic heart disease to a patient with a previous myocardial infarction. If nocturnal hypotension occurs, the dose should be reduced or the drug should be discontinued.

Cardiovascular effects of topical carteolol hydrochloride and timolol maleate in patients with ocular hypertension and primary open-angle glaucoma. Night Study Group

PURPOSE

To compare the effects of topical timolol maleate 0.5% and carteolol hydrochloride 1% on pulse rate and blood pressure.

METHODS

In a randomized, double-masked, parallel-design, multicenter clinical trial, we compared the effects of timolol and carteolol on pulse rate and blood pressure measured by 24-hour ambulatory blood pressure monitoring in 169 adult patients with either ocular hypertension or primary open-angle glaucoma.

RESULTS

From noon to 8 PM, baseline mean pulse rate of 82 to 83 beats per minute (bpm) had decreased by 4 to 6 bpm in both groups after 4 weeks of therapy with timolol or carteolol. From midnight to 4 AM, the pulse rate in the carteolol group was significantly above baseline (P = .005), while the timolol group was significantly below baseline (P < .001). Four times as many patients became bradycardic (heart rate, < 60 bpm) on timolol (18.4%) as did patients on carteolol (4.5%) from midnight to 4 AM. More than twice as many patients exhibited a resolution of their bradycardia with carteolol (46.7%) as did patients treated with timolol (18.2%) from midnight to 4 AM. Overall cardiovascular adverse effects were reported significantly more frequently in the timolol than the carteolol group (P = .002).

CONCLUSIONS

Timolol causes significantly lower mean heart rate during the nighttime and more nocturnal bradycardia than carteolol does in patients with ocular hypertension and primary open-angle glaucoma. These differences may be because of the intrinsic sympathomimetic activity of carteolol.

Coronary haemodynamics in left ventricular hypertrophy

BACKGROUND

Left ventricular hypertrophy is associated with an increased risk of cardiovascular morbidity and mortality. Previous studies have shown that patients with left ventricular hypertrophy develop electrocardiographic changes and left ventricular dysfunction during acute hypotension, and suggest that the lower end of autoregulation may be shifted upwards.

AIM

To measure coronary blood flow (velocity) and flow reserve during acute hypotension in patients with left ventricular hypertrophy.

PATIENTS

Eight patients with atypical chest pain and seven with hypertensive left ventricular hypertrophy; all with angiographically normal epicardial vessels.

SETTING

Tertiary referral centre.

METHODS

The physiological range of blood pressure was determined by previous ambulatory monitoring. Left ventricular mass was determined by echocardiography. At cardiac catheterisation, left coronary blood flow velocity was measured using a Judkins style Doppler tipped catheter. During acute hypotension with sodium nitroprusside, coronary blood flow velocity was recorded at rest and during maximal hyperaemia induced by intracoronary injection of adenosine. Quantitative coronary angiography was performed manually.

RESULTS

For both groups coronary blood flow velocity remained relatively constant over a range of physiological diastolic blood pressures and showed a steep relation with diastolic blood pressure during maximal hyperaemia with intracoronary adenosine. Absolute coronary blood flow (calculated from quantitative angiographic data), standardised for left ventricular mass, showed reduced flow in the hypertensive group at rest and during maximal vasodilatation.

CONCLUSION

The results are consistent with an inadequate blood supply to the hypertrophied heart, but no upward shift of the lower end of the autoregulatory range was observed.

Efficacy of long-term treatment with nipradilol, a nitroester-containing beta-blocker, in patients with mild-to-moderate essential hypertension

The effects of long-term treatment with nipradilol, a nitroester-containing beta-blocker, on casual and 24-hour blood pressures were studied in 70 patients with mild-to-moderate essential hypertension. Antihypertensive effects of nipradilol on casual blood pressure were observed in 68% of patients. Nipradilol reduced pulse rates, but no bradycardia was observed. The usefulness of nipradilol in the present study was 65%. The results of ambulatory blood pressure monitoring indicated that nipradilol reduced systolic blood pressure more than diastolic blood pressure, and reduced blood pressure during waking more than during sleep. These results suggest that nipradilol is a safe and useful long-term antihypertensive drug in both young and older patients with mild-to-moderate essential hypertension. When administered twice daily, nipradilol is effective throughout a 24-hour period.

Pharmacological management of hypertension in paediatric patients. A comprehensive review of the efficacy, safety and dosage guidelines of the available agents

The prevalence of hypertension in children, although lower than in adults, is still significant. An underlying cause is often identified in the younger patient, with essential hypertension accounting for the majority of cases in adolescents. The natural history of hypertension in childhood is still not well delineated. Previous Task Force recommendations are addressed to reflect current experience with the newer classes of agents, namely the angiotensin converting enzyme (ACE) inhibitors and the calcium channel blockers (CCBs) where either limited or no experience was previously available. In addition, the current treatment recommendations of Joint National Committee V (JNCV) are reflected in our discussion. The current drug classes are reviewed with respect to dosage guidelines, adverse effects and potential drug-drug interactions. The advantages and disadvantages of a tailored or individualised therapeutic approach as opposed to rigid stepped care therapy will be presented. Clearly, more long term data need to be obtained with respect to the safety and efficacy of the newer classes of drugs.

Antihypertensive therapy and circadian blood pressure profiles: a retrospective analysis utilising cumulative sums

The results of previous studies on the effects of antihypertensive agents on circadian blood pressure patterns are inconclusive, possibly due to the lack of a simple, objective, universally accepted method of quantifying circadian blood pressure profiles. In order to investigate for differences in the effects of antihypertensive drugs on circadian changes we utilised a recently described modified cumulative sums technique to quantify circadian alteration magnitude (CAM). CAM is simply calculated as the difference between crest and trough blood pressures, the mean blood pressures of the 6-h periods of highest and lowest sustained pressures respectively. The records from all 24-h ambulatory blood pressure monitoring performed over a 7 year period on subjects either on no medication (1208), or on treatment with a single first-line antihypertensive agent (578), were examined retrospectively. A sample (n = 40) stratified for trough diastolic blood pressure, age and sex was randomly selected from each of the following 5 groups: subjects on no medication, and subjects being treated with bendrofluazide, atenolol, class 2 calcium-channel blockers or captopril alone. Untreated subjects, those on bendrofluazide and those on a class 2 calcium channel blocker had similar circadian patterns. Subjects on atenolol therapy (25.9 +/- 1.7/18.3 +/- 1.3, systolic CAM +/- SE/diastolic CAM +/- SE) had attenuated circadian changes (p < 0.05) when compared to the untreated group (29.8 +/- 1.8/23.6 +/- 1.1), while those on captopril (34.9 +/- 2.4/25.7 +/- 1.8) exhibited markedly increased systolic and diastolic circadian blood pressure swings, which differed from those of the atenolol treated group (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of effects of propranolol versus pindolol on sinus rate and pacing frequency in sick sinus syndrome

Beta blockers in patients with sick sinus syndrome (SSS) may prevent supraventricular arrhythmias, systemic hypertension and myocardial ischemia, but may cause excessive depression of sinus node function. In 8 patients with SSS and a permanent pacemaker, the effect of chronic oral pindolol on sinus rate and pacing frequency was compared with that of propranolol in a double-blind crossover trial. In all patients the pacemaker was programmed to a rate of < or = 50 beats/min. Holter monitors, obtained at baseline and on each drug, were used to calculate peak ambulatory sinus rate, number of paced beats per day, maximal number of paced beats per hour, and percentage of hours with paced beats. The peak sinus rate with pindolol therapy was 24% higher than with propranolol (p = 0.001). During pindolol therapy, the number of paced beats per day and maximal paced beats per hour were reduced 54% (p = 0.04) and 61% (p = 0.02), respectively, compared with propranolol. Patients with SSS who require beta-blocker therapy for tachycardia, systemic hypertension or angina pectoris may have less bradycardia when treated with pindolol rather than propranolol. Beta blockers like pindolol, which cause less sinus node depression, may obviate the need for prophylactic permanent pacemakers in patients with SSS, and may help to prevent chronotropic incompetence and pacemaker syndrome in patients already treated with a VVI device.

Ambulatory blood pressure monitoring and circadian variation of cardiovascular disease; clinical and research applications

Ambulatory blood pressure monitoring is an evolving technology. It has an established role in the diagnosis of hypertension, the clinical management of selected patients, and in the evaluation of new medication. From continuous recording much has been learned about the circadian nature of blood pressure and heart rate. Future research holds promise for a greater understanding of the mechanisms and treatment of cardiovascular disease. The purpose of this short review is to describe the development of ambulatory blood pressure monitoring, and outline some of its important contributions to date; and also to explore the research potential and clinical utility of advanced intravascular monitoring techniques, such as the continuous recording of pulmonary artery pressure in ambulant patients.

Atenolol. A reappraisal of its pharmacological properties and therapeutic use in cardiovascular disorders

Atenolol is a selective beta 1-adrenoceptor antagonist with a duration of activity of at least 24 hours. The scope of therapeutic use of the drug has been expanded and become better defined since it was first reviewed in the Journal in 1979. Atenolol is effective and generally well tolerated in patients with all grades of hypertension. Data from comparative studies show that when administered orally, atenolol reduces blood pressure to a similar extent, and in a similar proportion of patients, as usual therapeutic doses of other beta-adrenoceptor antagonists (such as acebutolol, celiprolol, betaxolol, indenolol, metoprolol, nadolol, pindolol, propranolol, tertatolol), angiotensin converting enzyme (ACE) inhibitors (e.g. captopril, enalapril and lisinopril), calcium antagonists (e.g. amlodipine, diltiazem, felodipine, isradipine, nitrendipine, nifedipine, verapamil), doxazosin, ketanserin and alpha-methyldopa. Atenolol effectively lowers blood pressure in elderly patients with hypertension and in women with hypertension associated with pregnancy, and improves objective and subjective indices in patients with stable angina pectoris. Oral atenolol is used for preventing recurrence of supraventricular arrhythmias once control is achieved by intravenous administration of atenolol. Early intervention with intravenous atenolol followed by oral maintenance therapy reduces infarct recurrence and cardiovascular mortality in patients with known or suspected myocardial infarction. There is also encouraging evidence of reduced mortality from cardiovascular disease during long term therapy with atenolol in patients with hypertension. Atenolol is well tolerated in most patients. Increases in plasma levels of both total triglycerides and very low density lipoprotein (VLDL) triglycerides have accompanied atenolol therapy although the clinical relevance, if any, of longer term metabolic effects has yet to be determined. Its low lipid solubility and limited brain penetration results in a lower incidence of central nervous system effects than that associated with propranolol. After many years of clinical usage atenolol is a well established treatment option in several areas of cardiovascular medicine such as mild to moderate hypertension and stable angina pectoris. Furthermore, it has also shown potential in the treatment of some cardiac arrhythmias and has been associated with reduced cardiovascular mortality in patients with hypertension and in patients with myocardial infarction.

Blood pressure during sleep: antihypertensive medication

To investigate whether excessive reduction of blood pressure (BP) by antihypertensive medications correlates with myocardial infarction, especially during sleep in elderly patients, we used telemetry and cuvette dye-dilution methods to assess the direct BP and the hemodynamics of 68 inpatients with essential hypertension during wakefulness and sleep. There were 25 patients greater than or equal to 60 years old (OH-group) and 43 were less than or equal to 59 years old (YH-group). Of the OH-group, 36% showed high BP during the day, with marked decreases (minimum BP less than 110/70 mm Hg) during sleep. Average cardiac index (CI) of the OH-group was low during wakefulness and extremely low during slow-wave sleep. Changes of mean BP in the OH-group correlated with changes in total peripheral vascular resistance index (TPRI) during sleep, but this correlation was not observed in the YH-group. The antihypertensive effects on nocturnal BP of the various medications was: central adrenergic inhibitors less than or equal to beta blockers with intrinsic sympathomimetic activity less than or equal to alpha (alpha beta) blockers less than or equal to angiotensin-converting enzyme inhibitors less than or equal to calcium antagonists. Because BP and CI were found to be very low and TPRI seems to play an important role in BP regulation in sleeping elderly patients, excessive antihypertensive medication may be harmful to this subgroup. However, because the effects on nocturnal BP differ among various antihypertensive treatments, further research is required on the relation between antihypertensive medication and the hemodynamics of sleeping elderly hypertensive patients.

Beta-blockers and central nervous system side effects

Beta-adrenergic blocking drugs are a widely used, well tolerated and effective treatment for a variety of cardiovascular and noncardiovascular disorders. Over the years, beta-blockers have been associated with an incidence, albeit low, of CNS side effects. The question of interest, however, is whether the incidence is the same for all members of the class or whether other properties, such as hydrophilicity, have a bearing on the incidence of this type of side effect? This article addresses this question. In pharmacokinetic terms the lipophilic beta-blockers have been shown, both in animals and man, to readily cross the blood-brain barrier in contrast to hydrophilic beta-blockers. This is thought to have possible clinical relevance with respect to the relative incidence of CNS side-effects. To clarify the situation every published clinical paper, in which the beta-blockers propranolol (highly lipophilic, nonselective, no intrinsic sympathomimetic activity (ISA)), pindolol (moderately lipophilic, nonselective, moderate ISA), metoprolol (moderately lipophilic, beta 1-selective, no ISA) and atenolol (hydrophilic beta 1-selective, no ISA) were compared, was assessed for information pertaining to CNS side effects. This comprehensive review of the literature has shown, with few exceptions, that the incidence of CNS side effects such as sleep disturbances, dreaming, nightmares and hallucinations following clinically accepted doses of the four beta-blockers under scrutiny is generally low and that effects on short-term memory are minimal or absent. However, within this group of four drugs the incidence of these side effects is lowest with hydrophilic atenolol and generally highest with pindolol and propranolol. Metoprolol occupies an intermediate position. This order is in agreement with the pharmacokinetic observation that the more hydrophilic the molecule, the less is found in the brain tissue of both animals and man, although in the case of pindolol other factors may be important. The clinical relevance of studies involving psychometric testing is not clear.

Measurement and cardiovascular relevance of partial agonist activity (PAA) involving beta 1- and beta 2-adrenoceptors

In the normal heart the ratio of beta 1/beta 2-receptors in both atria and ventricles is about 75:25; in the failing heart the ratio is about 60:40. Stimulation of either beta 1- or beta 2-receptors results in a positive chronotropic and inotropic response. In the periphery, with the exception of lipolysis, renin release, control of intraocular pressure and intestinal relaxation, beta 2-related activity predominates. The nature of the beta 2-receptor is being unravelled and it has now been cloned. The beta-receptor antagonist is 'anchored' via disulfide bonding. Subsequent events involve the regulatory protein guanine nucleotide which couples the receptor to adenylate cyclase. beta-receptor density may by up- or down-regulated. beta-stimulation down-regulates (uncouples and internalizes or sequestrates) and beta-antagonism up-regulates beta-receptor numbers, but the functional implications of such changes are not always clear. A partial agonist occupies a receptor site and competitively inhibits the full agonist (e.g. noradrenaline). A partial agonist differs from a full agonist in that maximal response of a tissue is less. When background sympathetic activity is absent or very low a partial agonist will act as an agonist, e.g. increase heart rate, but when background tone is high the partial agonist will behave functionally as an antagonist, e.g. decrease heart rate. In animals partial agonist activity (PAA) can be assessed in many ways. In the catecholamine-depleted (reserpine or syrosingopine), vagotomized or pithed, intact animal beta-activity can be assessed via changes in heart rate, cardiac contractility and atrioventricular conduction. Isolated organs can also be used such as atria, papillary muscle, tracheal, mesenteric artery and uterine preparations. The choice of animal is important as marked species differences in response can occur. In man assessing PAA is difficult due to the presence of an intact sympathetic system: the problem can be overcome by autonomic blockade of constrictor and vagal reflexes with prazosin, clonidine and atropine but leaving the beta-receptor mediated responses unimpaired. beta 1- and beta 2-selective PAA can also be gauged via an increased sleeping heart rate (basal sympathetic tone) in the presence and absence of a beta 1- and beta 2-selective antagonist. beta 1-selective PAA can also cause an increase in resting systolic blood pressure, beta 2-selective PAA may be further assessed by a fall in DBP, increased blood flow, fall in peripheral resistance or increased finger tremor.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of age on the nocturnal fall of blood pressure and its modulation by long-acting calcium antagonists

The clinical significance of the nocturnal fall of blood pressure (BP) was examined. BP was monitored every 5 min for 24 hrs by means of a finger volume oscillometric device. The nocturnal fall was observed in all age groups (young: less than 40, n = 49; adult: 40 less than or equal to less than 60, n = 110; old: 60 less than or equal to, n = 33). The amplitude of nocturnal fall of BP (averaged daytime blood pressure--averaged nighttime blood pressure) in old patients (systolic = 13 +/- 11, diastolic = 10 +/- 8 mmHg, mean +/- SD) was similar to that in the young patients (systolic = 11 +/- 8, diastolic = 10 +/- 8 mmHg). These 192 subjects were also classified according to mean BP level (MBP) averaged for daytime in the ambulatory blood pressure monitoring records [MBP less than 85 (mmHg), n = 31; 85 less than or equal to MBP less than 100, n = 72; 100 less than or equal to MBP less than 115, n = 49; 115 less than or equal to MBP, n = 25]. BP level did not affect the pattern of circadian variation in the normal subjects or in the essential hypertensive patients at WHO stage I or II. The amplitude of the nocturnal fall in systolic BP increased with the increase in BP level, but this was not the case with diastolic BP (mean daytime BP less than 85 mmHg: systolic = 11 +/- 8, diastolic = 8 +/- 6 mmHg; 85 less than or equal to less than 100: systolic = 14 +/- 8, diastolic = 11 +/- 6 mmHg; 100 less than or equal to less than 115: systolic = 17 +/- 9, diastolic = 11 +/- 8; 115 less than or equal to: systolic 17 +/- 8, diastolic = 11 +/- 6 mmHg). Nitrendipine (8.6 +/- 5.6 mg, 22.5 +/- 11.4 days, n = 14) and nisoldipine (9.3 +/- 6.2 mg, 21.5 +/- 11.4 days, n = 15) administered once daily in the morning or nifedipine slow release tablet, 20 mg twice daily (n = 15, 17.7 +/- 5.2 days) induced a significant downward shift in the circadian BP pattern, in other words, the hypotensive effect was also observed during the night when the BP had already been low. Taken together, the information on the nocturnal behavior of BP would be valuable, especially in treating aged patients with essential hypertension with a long-acting antihypertensive drug.

Antihypertensive treatment, myocardial infarction, and nocturnal myocardial ischaemia

Patients with critical coronary stenoses or hypertrophied ventricles have impaired coronary vasodilator reserve and are at greatest risk of myocardial ischaemia or infarction if subendocardial perfusion pressure falls below the lower threshold of bloodflow autoregulation. During sleep, antihypertensive treatment may cause coronary artery perfusion pressure to fall below these limits in such patients. Unrecognised nocturnal hypotension may be one reason why treatment has not diminished the risk of myocardial infarction in patients with hypertension.

Blood pressure monitoring outside the office for the evaluation of patients with resistant hypertension

Although severe hypertension is associated with a poor prognosis, there exists a substantial number of patients who have persistently elevated blood pressures, but no signs of target organ damage, and nearly normal life expectancy. In such cases, measurement of blood pressure outside the clinic may give readings that are as much as 30 mm Hg lower than the clinic readings. The first step recommended in the identification of such patients is to use home blood pressure monitoring. If home blood pressures are low, 24-hour ambulatory blood pressure recording is indicated. If this also gives low readings, it is appropriate to treat patients according to their level of home blood pressure. Because of the unreliability of clinic pressures, ambulatory and home blood pressure monitoring may also be of value in assessing the response to treatment.

Enalapril and atenolol in essential hypertension: attenuation of hypotensive effects in combination

In 16 patients with essential hypertension the effects of enalapril 20 mg once daily were compared with those of atenolol 50 mg once daily, with the two drugs in combination and with placebo using a double-blind cross-over design with allocation of treatment order by randomised Latin squares. For each patient there were four treatment phases, each of four weeks duration, which together comprised a 2 x 2 factorial experiment. All blood pressure parameters were reduced in the three active treatment phases compared to placebo (p less than 0.001). Supine blood pressures (group means) were 171/97 (placebo), 147/85 (enalapril), 154/84 (atenolol) and 144/78 (enalapril plus atenolol) (S.E.M. +/- 2/+/- 1-ANOVA), and standing blood pressures were 170/105 (placebo), 146/92 (enalapril), 154/92 (atenolol) and 147/86 (enalapril plus atenolol) (S.E.M. +/- 3/+/- 1). In the combination phase there was an additional hypotensive response but the potential fully additive effects of the two agents were attenuated by 30-50%. The mechanism of the attenuated hypotensive effect of the combined agents has not been determined. Plasma atrial natriuretic peptide (ANP) concentration was doubled in the presence of atenolol (P less than 0.01) suggesting that ANP may contribute to the hypotensive effect of the beta-blocker.

Pharmacokinetics of long acting propranolol. Implications for therapeutic use

Beta-adrenoceptor antagonists are among the most commonly prescribed classes of drugs. They are indicated for the treatment of diseases such as hypertension and angina pectoris, in which long term therapy is often required. Since many beta-adrenoceptor antagonists have short plasma elimination half-lives, divided daily dosing has often been necessary in order to provide continuous beta-blockade throughout the day. However, such multiple-dose schedules may promote patient non-compliance and failure of the prescribed regimen. Long acting propranolol is a sustained release formulation of propranolol which has been developed to maintain therapeutic plasma propranolol concentrations throughout a 24-hour period while allowing once-daily dosing. Compared with conventionally formulated propranolol, long acting propranolol has a prolonged terminal half-life (8 to 11 hours), due to slower absorption from the gut. Systemic bioavailability of long acting propranolol is 30 to 50% less than that of the conventional formulation. This difference may result from increased hepatic metabolism. Peak drug concentrations are significantly lower than following identical doses of conventional propranolol, and the time to peak drug concentrations following administration is delayed. Relatively constant plasma concentrations and clinically significant inhibition of exercise-induced tachycardia are maintained throughout a 24-hour dosing interval following once-daily long acting propranolol. Once-daily long acting propranolol is as effective as divided doses of conventional propranolol for the treatment of hypertension and angina pectoris. Efficacy also appears comparable with once-daily administration of long acting conventional beta-adrenoceptor antagonists such as atenolol and nadolol. Once-daily long acting propranolol provides clinically significant sustained beta-adrenoceptor blockade and offers the potential for improved patient compliance due to once-daily dosing. Since provision of sustained beta-adrenoceptor blockade appears to be particularly important in the treatment of angina, this may be the principal indication for which long acting propranolol has a therapeutic advantage independent of its potential to improve compliance.

Effects of beta-adrenoceptor blockade on heart rate and physiological tremor in diabetics with autonomic neuropathy. A comparative study of epanolol, atenolol and pindolol

Eight diabetics with autonomic neuropathy were given single oral doses of epanolol (200 mg), atenolol (50 mg), pindolol (5 mg) and placebo in a double-blind randomised order at weekly intervals. Supine resting heart rate, physiological tremor and blood glucose were measured before, 2 and 4 h after dosing, and ambulatory heart rate monitored for 24 h. Supine resting heart rate was significantly lowered by atenolol both at 2 and 4 h, and increased on pindolol at 4 h. Heart rate was unaffected by epanolol compared with placebo. Heart rate during the 'waking' period (14.00-23.00 h) was lower than placebo after epanolol and atenolol but unaffected by pindolol. During the 'sleeping' period (23.00 h-08.00 h) heart rate was significantly increased by pindolol, lowered with atenolol and unaffected on epanolol. Pindolol significantly increased physiological tremor at 4 h. No differences were seen between epanolol, atenolol and placebo. Plasma glucose was significantly increased by pindolol 2 h after dosing. These results suggest that pindolol probably produces its partial agonist activity at both beta 1- and beta 2-adrenoceptors, while the partial agonist activity of epanolol is beta 1-selective. Despite abnormal cardiovascular reflex tests in these diabetics, the heart rate responses obtained in this study after beta-adrenoceptor blockade were surprisingly normal, and suggest that the concept of 'cardiac denervation' in diabetes requires modification.

Metoprolol. An updated review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy, in hypertension, ischaemic heart disease and related cardiovascular disorders

During the intervening years since metoprolol was first reviewed in the Journal (1977), it has become widely used in the treatment of mild to moderate hypertension and angina pectoris. Although much data have accumulated, its precise mechanisms of action in these diseases remain largely uncertain. Optimum treatment of hypertension and angina pectoris with metoprolol is achieved through dose titration within the therapeutic range. It has been clearly demonstrated that metoprolol is at least as effective as other beta-blockers, diuretics and certain calcium antagonists in the majority of patients. Although a twice daily dosage regimen is normally used, satisfactory control can be maintained in many patients with single daily doses of conventional or, more frequently, slow release formulations. Addition of a diuretic may improve the overall response rate in hypertension. Several controlled trials have studied the effects of metoprolol administered during the acute phase and after myocardial infarction. In early intervention trials a reduction in total mortality was achieved in one moderately large trial of prolonged treatment, but in another, which excluded patients already being treated with beta-blockers or certain calcium antagonists and where treatment was only short term, mortality was significantly reduced only in 'high risk' patients. Overall results with metoprolol have not demonstrated that early intervention treatment in all patients produces clinically important improvement in short term mortality. Thus, the use of metoprolol during the early stages of myocardial infarction is controversial, largely because of the requirement to treat all patients to save a small number at 'high risk'. This blanket coverage approach to treatment may be more justified during the post-infarction follow-up phase since it has been shown that metoprolol slightly, but significantly, reduces the mortality rate for periods of up to 3 years. Metoprolol is generally well tolerated and its beta 1-selectivity may facilitate its administration to certain patients (e.g. asthmatics and diabetics) in whom non-selective beta-blockers are contraindicated. Temporary fatigue, dizziness and headache are among the most frequently reported side effects. After a decade of use, metoprolol is well established as a first choice drug in mild to moderate hypertension and stable angina, and is beneficial in post-infarction patients. Further study is needed in less well established areas of treatment such as cardiac arrhythmias, idiopathic dilated cardiomyopathy and hypertensive cardiomegaly.

Twice-daily verapamil for hypertension: a comparison with propranolol

Recent reports have confirmed that some slow calcium channel inhibitors have useful antihypertensive properties because they produce dilatation of the peripheral arterioles without reflex tachycardia. Verapamil is such a drug, but its clinical role in the management of hypertension is not clear. An open crossover trial was performed to compare the 24-hour profiles of blood pressure reduction after long-term therapy with a standard beta-adrenoceptor blocker, propranolol, and verapamil. Nineteen patients were studied by continuous ambulatory intraarterial recording and the order of drug administration was determined by random allocation. The drugs were administered 2 times a day and titrated according to casual clinic pressures (propranolol, 40 to 240 mg 2 times a day; verapamil, 120 to 240 mg 2 times a day). Mean hourly blood pressure and heart rate values were obtained over a 24-hour cycle and the responses to isometric and dynamic exercise were also examined. The drugs produced a uniform and comparable reduction in blood pressure throughout the day, together with a reduction in heart rate, which was greater with propranolol. Comparable effects were also seen on the pressor responses to exercise. Both drugs were equally well tolerated and caused no patient withdrawals. Thus, oral verapamil given 2 times a day shows a degree of efficacy similar to that of propranolol and provides 24-hour blood pressure control. This slow calcium channel inhibitor was well tolerated and may be used as initial therapy for hypertension.

A comparison of atenolol and long-acting trimazosin in mild to moderate essential hypertension

In a 12-week double-blind randomised study the efficacy of atenolol and a new longer-acting formulation of trimazosin were compared when given once daily in patients with mild to moderate hypertension. Two parallel groups, each consisting of 18 patients, were studied. At randomisation the two groups were well matched for age and sex distribution. They were also well matched for blood pressure, pulse rate and body weight; these latter measurements were recorded at regular intervals during the 12 weeks of study. Atenolol produced substantial reduction in both systolic and diastolic blood pressure, and in heart rate, during 12 weeks of treatment. This therapeutic effect was maintained until the next dose after 24 hours. Trimazosin, by comparison, failed to reduce either systolic or diastolic pressure, or to alter heart rate. Side effects were minor with both agents and compliance with treatment was good. Atenolol caused significant elevation of plasma concentration of triglyceride, with reduction in high density lipoprotein concentration when compared with trimazosin. In conclusion, atenolol was confirmed as an effective agent for the treatment of mild to moderate hypertension. By comparison trimazosin in the longer-acting formulation was ineffective in this study. However, trimazosin may still find a place in treatment if used at higher dose.

Propranolol versus verapamil for the treatment of essential hypertension

Recent reports have confirmed that slow calcium channel inhibitors have useful antihypertensive properties because they produce dilatation of the peripheral arterioles without reflex tachycardia. Their clinical place in the management of hypertension has yet to be clearly defined, and thus we have performed an open crossover trial to compare the 24-hour profiles of blood pressure reduction after chronic therapy with propranolol and verapamil. Nineteen patients were studied by continuous ambulatory intraarterial recording and the order of drug administration was decided by random allocation. Drug dosage was twice daily and titrated according to casual clinic pressures (propranolol, 40 to 240 mg twice a day; verapamil, 120 to 240 mg twice a day). Mean hourly blood pressure and heart rate values were obtained over a 24-hour cycle, and the responses to isometric and dynamic exercise were also examined. Both drugs were shown to produce a uniform and comparable reduction in blood pressure throughout the whole day, together with a reduction in heart rate, which was greater with propranolol. Comparable effects were also seen on the pressor responses to exercise. Both drugs were equally well tolerated and caused no patient withdrawals. We conclude that oral verapamil given twice daily showed a similar degree of efficacy to propranolol and provided 24-hour blood pressure control. This slow calcium channel inhibitor may be useful as initial therapy for hypertension, particularly for those patients in whom beta-adrenoreceptor blockers are contraindicated.

Intrinsic sympathomimetic activity: physiological reality or marketing phenomenon

Intrinsic sympathomimetic activity (ISA) describes the partial beta-adrenergic agonist responses elicited by a series of beta-adrenergic antagonists. The dual effect on the beta-adrenergic receptor appears to be related to structural specificity of the drugs allowing competitive binding to the receptor (antagonist activity) and partial interaction at the receptor's activation site (agonist activity). The clinical effects of a beta-adrenergic antagonist with ISA depend on the relative balance of the drug's inherent antagonist and agonist activity and on the degree of underlying sympathetic tone in the patient. Theoretically, the agonist activity may be beneficial in the patient in whom beta-adrenergic antagonists are indicated, but who has concomitant bradycardia and/or mild to moderate congestive heart failure or compromised pulmonary function, or in the patient being withdrawn from beta-adrenergic antagonist therapy. There is positive evidence from clinical trials that in select patient populations a few of these benefits of ISA are afforded without compromise to beta-adrenergic antagonist activity. However, predisposing factors such as acute illness and individual idiosyncrasies may interfere with the manifestations of the agonist effects. Further, maximal response to full beta-adrenergic agonists will be diminished by concurrent therapy with beta-adrenergic antagonists regardless of ISA presence. In summary, ISA does have a physiological basis and increased experience in larger patient populations will help to place it in proper clinical perspective.

Long acting beta-blockers in the twenty fourth hour

Fifteen mild to moderate hypertensives were submitted to exercise testing using a bicycle ergometer with a fixed load. Heart rate, blood pressure and ECG were recorded throughout 5 min exercise and 10 min recovery. Oxygen uptake was measured during the final minute of exercise and blood glucose estimation and serum drug levels assessed 5 min after recovery. The above measurements were made after exactly 24 h following seven days administration of 160 mg of long acting (L.A.) propranolol, 200 mg of sustained action (S.A.) metoprolol and two matched placebos. Propranolol L.A. was superior to Metoprolol S.A. in the reduction of exercise induced tachycardia and both drugs were significantly superior to placebos. Both drugs were effective agents for the lowering of resting blood pressure after 24 h but propranolol L.A. was more effective in the lowering of systolic peaks observed during exercise. There was no significant effect upon oxygen uptake and blood glucose. The incidence of side effects was low and showed no significant difference from placebo.