The possible role of the ancillary properties of beta adrenoceptor antagonists in the management of angina pectoris

Beta adrenoceptor antagonists are effective in the symptomatic management of angina pectoris. This paper examines critically the possible influence of the ancillary properties of beta 1 selectivity, partial agonism and membrane-stabilizing action on the response in anginal patients. The response is categorized according to experimental, pharmacological and clinical endpoints, placing emphasis on the possible errors which may arise from extrapolation from the former to the latter. It is concluded: That selective beta adrenoceptor antagonism confers limited, but tangible advantages over non-selective antagonists in regard to patients with reversible airways obstruction, and also in the metabolic and haemodynamic response to acute hypoglycaemia. Cardioselectivity does not influence the central haemodynamic response to exercise, but lessens adrenaline-mediated hypertensive responses to smoking and hypoglycaemia. Non-selective partial agonists cause less reduction in resting ventricular function, but their effects on cardiac output during exercise are indistinguishable from full antagonists. Membrane stabilizing properties have a marked influence on the tolerability of these agents in terms of unwanted, nonspecific central nervous system symptoms. Unresolved questions relate to the influence of partial agonism on fatigue, metabolic responses, especially blood lipids and glucose, and the possibility of lesser efficacy in angina compared to full antagonists.

Urologic complications of nonurologic medications

A physician must be aware of common drug side effects and interactions before prescribing a certain agent. In addition to the drugs that we, as urologists, prescribe, we must also be aware of the urologic side effects of drugs that are commonly prescribed by nonurologists. The mechanisms of the pharmacologic causes for voiding dysfunction, erectile and sexual dysfunction, infertility, and urolithiasis are often mutifactorial and incompletely understood. The recognition and association of a particular drug's potential side effects may save valuable time and money involved in the workup of a patient with a new urologic complaint. It is incumbent on the practicing urologist to be able to recognize the common, and sometimes subtle, urologic complications of medications that are used for nonurologic conditions.

The applied pharmacology of beta-adrenoceptor antagonists (beta blockers) in relation to clinical outcomes

Despite the fact that beta blockers were introduced into clinical practice 25 years ago, new beta blockers with differing kinetic and dynamic profiles continue to be developed and marketed. This overview assesses some of the more extensively studied agents from the point of view of proof of utility and the validity of claims for therapeutic advances. The clinical data suggests that despite the expectations of improvements based on kinetic and dynamic consideration, none of the newer agents have been shown unequivocally, either in terms of efficiency or tolerability, to be an advance over the reference agents, the beta 1 antagonists atenolol and metoprolol. This may be either because such improvements will not occur or because of shortcomings in the design and duration of comparative studies. There are trends to suggest that celiprolol has lesser effects on bronchial function and that it has a lesser impact on lipoprotein profiles. Approaches are suggested that might enable clinicians to appraise for themselves the validity of claims for the improved efficiency of new beta blockers.

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)

A comparative study of doxazosin versus atenolol in mild-to-moderate hypertension

Doxazosin, a quinazoline derivative, is a selective alpha 1-inhibitor that reduces calculated coronary heart disease risk by lowering blood pressure while favorably affecting blood lipid levels. The aim of this study was to compare the efficacy and toleration of doxazosin with atenolol, one of the most frequently used cardioselective beta-blockers in Italy. Forty patients with mild-to-moderate hypertension were treated with either atenolol (100 mg) or doxazosin (mean dose, 3.3 mg) once daily for 8 weeks. Both drugs significantly reduced supine and standing systolic and diastolic blood pressures. Atenolol induced marked bradycardia, whereas doxazosin had very little effect on heart rate. Doxazosin produced a favorable effect on blood lipid levels by decreasing triglyceride and total cholesterol levels and increasing high-density lipoprotein cholesterol and high-density lipoprotein total cholesterol ratio. Atenolol had exactly the opposite effect on blood lipid levels. Both drugs had equivalent toleration profiles. It was concluded that doxazosin was as effective as atenolol in reducing elevated supine and standing blood pressures. In addition, doxazosin had a beneficial effect on lipid profiles and minimal effect on heart rate. Therefore doxazosin may reduce calculated coronary heart disease risk in hypertensive patients.

A comparison of the side effects of atenolol and propranolol in the treatment of patients with hypertension

A single-blind study was conducted in 52 hypertensive patients, aged 25 to 68 years, to compare the side effects of an equally effective antihypertensive regimen of propranolol and atenolol. All patients had a history of side effects with beta-blocker therapy. Patients were treated with propranolol 40 to 160 mg bid for 8 weeks, followed by atenolol 50 to 100 mg given once daily for 8 weeks, and then rechallenged with the required dosage of propranolol for 8 weeks. Mean systolic and diastolic blood pressures were controlled during all three treatment phases. Side effects showed a definite trend toward improvement during the atenolol treatment phase. CNS side effects, in particular, showed significantly (P less than .05) reduced severity scores and overall incidence rates during the atenolol treatment phase. In conclusion, this study showed that at equally effective antihypertensive dosages the hydrophilic beta blocker atenolol produced significantly fewer CNS side effects than the lipophilic beta blocker propranolol.

Pharmacologic aspects of intrinsic sympathomimetic activity in beta-blocking drugs

The possession of intrinsic sympathomimetic activity (ISA) by a beta-adrenoceptor blocking drug results in a number of different pharmacologic properties. Most profound are the central hemodynamic effects. A drug with a significant degree of ISA results in less of a decrease in heart rate at rest and cardiac output, and, at least partly because of this, less of a decrease in peripheral blood flow. If prevailing sympathetic tone is low enough (e.g., during sleep) and the degree of ISA is sufficient, an increase in heart rate may be seen from an ISA-possessing drug. If the drug possesses beta 2 ISA, then a peripheral vasodilation action from stimulation of beta 2 vasodilator receptors may also be relevant. If high levels of exercise and full dosages of the drugs are used, a beta-blocking drug with ISA produces less of a decrease in heart rate. In asthmatic subjects, the modest beta-stimulant action on bronchial smooth muscle is not important, as these patients are potentially sensitive to any receptor blockade. Isoprenaline responses are inhibited to a similar degree compared with inhibition of exercise tachycardia, by nonselective drugs with and without ISA, whereas beta 1 selective agents produce much less inhibition of isoprenaline-induced tachycardia. A drug with ISA "down regulates" beta receptors; thus, when the drug is withdrawn there is no post-beta-blocking drug hypersensitivity in contrast to agents without ISA. There is evidence that ISA results in less of a disturbance in certain metabolic processes, particularly lipid metabolism and the metabolism of liver-metabolized drugs.

Comparison of atenolol 50 mg and 100 mg as initial treatment in uncomplicated mild to moderate hypertension

After screening a local population in the northern part of The Netherlands for hypertension, 59 patients with a diastolic pressure (DP) between 95 and 130 mmHg were randomized and treated either with 50 mg atenolol (n = 29) or 100 mg atenolol (n = 30) for 1 month. There was no significant difference between the two treatments, neither in the fall in systolic and diastolic pressures nor in the number of complaints reported. It is concluded that in the initial treatment of uncomplicated mild to moderate hypertension, 100 mg atenolol has no advantage over a 50 mg dose.

Atenolol versus pindolol: side-effects in hypertension

This randomized crossover out-patient study was designed to compare the antihypertensive effects of atenolol and pindolol. After a wash-out period of two weeks in pretreated cases, 107 patients with essential hypertension were given either atenolol 100 mg once-daily or pindolol 20 mg slow release (SR) once-daily. Both atenolol and pindolol lowered blood pressure over the 24 week period. The diastolic blood pressure reduction was significantly greater (p less than 0.01) with atenolol than with pindolol. Before beta-blocker therapy, many patients had already experienced side-effects such as fatigue, sleep disturbances and dreams. This probably relates to the high sensitivity of the analogue scale used to assess side-effects, and to the high incidence of such symptoms in untreated patients. As the study progressed there was a reduction in the frequency of fatigue (p less than 0.03) and dreams (p less than 0.05) in both groups, whereas sleep disturbances significantly increased under pindolol (p less than 0.05) but decreased under atenolol (p less than 0.05). The only important side-effect difference between the two beta-blockers was the higher incidence of sleep disturbances with pindolol which may be due to the higher lipophilicity of this beta-blocker.

Quantification of side-effects of beta-adrenoceptor blockers using visual analogue scales

We have devised a series of visual analogue scales (VAS) to measure the side-effects prevalent amongst hypertensive patients taking beta-adrenoceptor blockers, and we present the results of a pilot study. These show that the method is suitable for studying side-effects and suggest that patients on beta-adrenoceptor blockers experience a greater incidence of tiredness of the legs, (P = 0.001), cold digits (P = 0.005) and vivid dreaming (P = 0.01) when compared to hypertensive patients not taking beta-adrenoceptor blockers.

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

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