The assessment of β-adrenoceptor blocking drugs in hyperthyroidism

Comparative evaluation of cardioselectivity of metoprolol OROS and atenolol: a double-blind, placebo-controlled crossover study

Cardioselectivity of a single oral dose of metoprolol oral osmotic (OROS) (14/190 mg) and atenolol (100 mg) was compared in 12 patients with reversible obstructive airway disease by assessing the dose-response curve to increasing doses of inhaled salbutamol. The beta-blocking activity of the two drugs, which was determined by measuring heart rate, blood pressure, and derived indexes at peak plasma drug levels, was similar. Both metoprolol and atenolol significantly reduced forced vital capacity and peak expiratory flow, with no difference between drugs. Atenolol but not metoprolol also significantly reduced forced expiratory volume in 1 second and specific airway conductance. Both metoprolol and atenolol shifted the dose-response curve of specific airway conductance to the right. The results indicate that the new OROS delivery system for metoprolol, which produces a relatively constant plasma drug level, provides a cardioselectivity comparable to or greater than that of atenolol at maximum plasma levels.

Clinical assessment of beta blockade

This study was undertaken to assess a clinical measurement (leg squats) in order to determine the adequacy of beta-adrenergic blockade (AdBB) utilizing the symptom-limited exercise test heart rate of less than 120 beats/min as the standard. Seventy subjects were tested, 35 receiving beta-adrenergic-blocking drugs in clinically determined maximal doses, and 35 subjects not receiving these agents. Sensitivity (Se), specificity (Sp), and positive (Pv+) and negative (Pv-) predictive values were calculated for post-leg squat heart rates of less than or equal to 100, less than or equal to 110 and less than or equal to 120 beats/min. Other variables analyzed for AdBB were resting heart rates and post-leg squat heart rate increase greater than 50% over baseline. A cost-benefit analysis was also performed. It was concluded that: (1) Neither the resting heart rate or percent increase in heart rate compared to baseline reliably predicted AdBB. (2) In patients receiving beta-blocking drugs, a post-squat heart rate of less than or equal to 100 beats/min had a Se = .82, Sp = .67, Pv+ .70, and Pv- .80, values not high enough to be reliably used in many clinical situations. (3) If the post-squat heart rate was greater than 110 beats/min, however, AdBB is probably absent, since no subjects on beta blockers with maximum exercise test heart rate less than or equal to 120 beats/min had a post-leg squat heart rate greater than 110 beats/min. (4) For a reasonable range of cost and test performance estimates, utilization of the leg squat test as described here is favored on the basis of cost-benefit analysis.

Effects of S-adenosyl-methionine on plasma norepinephrine, blood pressure, and heart rate in healthy volunteers

S-adenosyl-methionine (SAMe) is currently undergoing trials as a possible antidepressant. Because SAMe's mechanism of action is obscure and norepinephrine (NE) is often implicated in affective disorders, we studied the effects of SAMe on this neurotransmitter in volunteers. Plasma NE and 3-methoxy-4-hydroxyphenylglycol (MHPG) in the supine and standing position were studied before and after acute placebo or a single 400 mg dose of SAMe and following seven daily administrations; concomitant measures were heart rate (HR) and blood pressure. Subjects were unable to distinguish acute drug from placebo, and although chronic SAMe administration was open, they reported no behavioral effects. Standing HR and plasma NE were reduced following chronic SAMe. Qualitatively similar changes are obtained following chronic treatment with monoamine oxidase inhibitors (MAOIs). However, unlike MAOIs, chronic SAMe treatment was not associated with changes in plasma MHPG. Exaggerated standing NE is found in depressed patients; SAMe may reduce this abnormal response, providing a clue for its mechanism of action in depression.

A comparison of propranolol and nadolol pharmacokinetics and clinical effects in thyrotoxicosis

For a comparison of propranolol and nadolol pharmacokinetics and clinical effects, 20 newly diagnosed patients with thyrotoxicosis were randomly selected to receive as sole therapy, either propranolol, 40 mg every 6 hours for 14 days, or nadolol, 80 mg each morning for 14 days. The study was repeated when the patients were in the euthyroid state. There was a similar and highly significant degree of beta blockade and amelioration of symptoms of thyrotoxicosis at the end of the dosage interval (trough), i.e., 24 hours after nadolol or 6 to 8 hours after propranolol. Trough and peak serum levels of propranolol were significantly lower when the patients were in a thyrotoxic state than when they were in a euthyroid state, whereas the pharmacokinetics of nadolol were not appreciably altered by thyrotoxicosis. In thyrotoxicosis, trough levels of propranolol and nadolol were significantly inversely correlated with derived creatinine clearance values. In the symptomatic treatment of thyrotoxicosis, nadolol, a once-daily nonmetabolized beta blocker, has certain advantages compared with propranolol. It is preferred by patients, is more convenient, and probably aids compliance.

Use of beta-adrenoceptor blocking drugs in hyperthyroidism

There is an increasing use and variety of beta-adrenoceptor blocking agents (beta-blockers) available for the treatment of hyperthyroidism. Recent comparative studies suggest that atenolol (200mg daily), metoprolol (200mg daily); acebutolol (400mg daily), oxprenolol ( 160mg daily), nadolol ( 80mg daily) and timolol (20mg daily) produce a beneficial clinical response equal to that seen with propranolol ( 160mg daily). Most beta-blockers reduce resting heart rate by approximately 25 to 30 beats/min, although a lesser reduction is seen with those possessing intrinsic sympathomimetic activity such as oxprenolol and pindolol. While earlier studies employing large doses of intravenous propranolol concluded that beta-blockade reduced myocardial contractility, more recent non-invasive studies suggest that the predominant cardiac effect is on heart rate. In patients with cardiac failure, beta-blockers may, however, produce a profound fall in cardiac output. Nevertheless, in combination with digoxin they may be useful in controlling the atrial fibrillation of thyrocardiac disease. beta-Blockers improve nervousness and tremor (although to a lesser extent with cardioselective agents) and severe myopathy, and they also reduce the frequency of paralysis in patients with thyrotoxic periodic paralysis. There is often subjective improvement in sweating but usually no major effect on eye signs. Recent studies show a 10% reduction in oxygen consumption/basal metabolic rate with long term oral use of selective or nonselective beta-blockers. In addition, many agents (propranolol, metoprolol, nadolol and sotalol but not acebutolol, atenolol or oxprenolol) reduce circulating tri-iodothyronine (T3) concentration by between 10 and 40%, although the clinical significance of this effect (if any) is not established. beta-Blockers may also have endocrinological effects on gastrin, cyclic AMP, catecholamines and other hormone levels. Given in adequate dosage, propranolol has been shown to control thyrotoxic hypercalcaemia. Minor side effects (nausea, headaches, tiredness, etc.) are quite common but overall beta-blockers are well tolerated by the thyrotoxic patient. The major use of these drugs is in symptomatic control while awaiting definitive diagnosis or treatment. As an adjunct to antithyroid drugs or radioactive iodine, beta-blockers will produce a satisfactory clinical response in the weeks to months before these forms of therapy produce a euthyroid state. beta-Blockers are more convenient than antithyroid drugs in the control of patients receiving therapeutic radioiodine, in that continuous therapy and assessment of biochemical response is possible.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of cimetidine on the relative cardioselectivity of atenolol and metoprolol in asthmatic patients

The effects of chronic cimetidine therapy on the pharmacodynamic properties of atenolol and metoprolol were assessed in eight asthmatic patients using a placebo-controlled trial. When atenolol and metoprolol were administered at doses which achieved an equivalent degree of beta1-adrenoceptor blockade, metoprolol caused a significantly greater reduction in mean forced expiratory volume in one second (FEV1). This demonstrates the greater cardioselectivity of atenolol. The reductions in mean FEV1 induced by either atenolol or metoprolol were each unaffected by cimetidine. Plasma levels of each of the beta-adrenoceptor blockers were not affected by the addition of cimetidine. The FEV1 in one patient was further reduced when cimetidine was administered with metoprolol, although there was no corresponding change in plasma levels of drug. In this patient there was no such further reduction in FEV1 with atenolol. This study has not provided evidence for a pharmacodynamic interaction between cimetidine and either atenolol or metoprolol, but further studies are indicated.

Effect of a single oral dose of propranolol on essential tremor: a double-blind controlled study

The effect of a single oral dose of propranolol (120 mg) on essential tremor was investigated in a double-blind, placebo-controlled study in 26 patients. Hand tremor was recorded by means of accelerometers, and its frequency and amplitude calculated by using spectrum analysis. Recordings were made before and 1 1/2 hours after drug or placebo administration. Pretreatment tremor ranged from 4.2 to 9.6 Hz (median, 6.9 Hz) in frequency and from 0.002 to 1.33 cm (median, 0.014 cm) in amplitude. Neither propranolol nor placebo affected the frequency of the underlying tremor. The amplitude of tremor was reduced by 43 +/- 11% (SEM) after propranolol (p less than 0.01) and by 12 +/- 8% after placebo (NS). The reduction observed after propranolol was significantly greater than that observed after placebo. The tremor response after propranolol correlated negatively with baseline frequency and positively with pretreatment amplitude, duration of tremor, and age of the patient. No significant relationships could be found between tremor response, serum propranolol levels, and degree of cardiac beta blockade as assessed by the inhibition of standing tachycardia. There was a clear tendency for patients with small tremor amplitude (less than 0.006 cm hand displacement) to show the least satisfactory response to propranolol. These results indicate that a single oral dose of propranolol is effective in producing a rapid and marked reduction of essential tremor. Measurement of pretreatment amplitude and frequency might be useful in predicting the therapeutic outcome in these patients.

Nadolol in thyrotoxicosis

1 Twenty outpatients with thyrotoxicosis received the non-selective beta-adrenoceptor antagonist nadolol as sole treatment for 3 weeks. 2 Clinical improvement as measured by reduction in thyrotoxicosis therapeutic index occurred during the first week of treatment and was continued thereafter, and was accompanied by a significant reduction in serum T3 and elevation of serum reverse T3. 3 As measured by reduction in exercise heart rate, during chronic dosing nadolol 160 mg once daily produced blockade of beta-adrenoceptors for 12 h in all patients and 24 h in all but 2. 4 Wide interindividual variability was noted in steady state plasma nadolol concentrations, in part related to age and renal function. 5 Steady state plasma nadolol concentrations were related to reduction in heart rate.

Control of severe thyrotoxicosis with potassium iodide and propranolol

Conventional preparation of thyrotoxic patients for surgery using thiouracils and iodides may not be possible because of either, inability to obtain satisfactory therapeutic levels of the drugs or idiosyncratic reactions to the drugs. An alterative regime using potassium iodide and propranolol in combination has previously been shown to be both safe and effective in the pre-operative control of mild to moderate thyrotoxicosis. The use of this combination in a patient with severe thyrotoxicosis is described. Potassium iodide and propranolol can be used successfully to prepare patients with all degrees of thyrotoxicosis for surgery.

Propranolol in the surgical treatment of hyperthyroidism, including severely thyrotoxic patients

The perioperative course of 44 hyperthyroid patients prepared for surgery with propranolol alone, including 11 with severe thyrotoxicosis was compared to that of 20 euthyroid patients prepared for surgery with carbimazole. Conventional propranolol at a dosage of 160 mg/day was frequently insufficient to produce a high degree of beta-adrenergic blockade, particularly in severely thyrotoxic patients. A greater than 25 per cent reduction in sitting pulse rate was associated with a high degree of beta-blockade. The clinical course of patients with mild or moderate thyrotoxicosis was similar to that of the patients prepared with carbimazole. In contrast, the course of severely thyrotoxic patients was complicated and, in addition to a higher preoperative propranolol dosage, these patients commonly required supplemental propranolol after operation. Although thyroid crisis did not occur in any patient, we cannot recommend the use of propranolol alone for the severely thyrotoxic patient.

Metoprolol and propranolol in essential tremor: a double-blind, controlled study

Single oral doses of propranolol (120 mg), metoprolol (150 mg) and placebo were given in a randomised, double-blind fashion to 23 patients with essential tremor. Both beta blockers were significantly more effective than placebo in reducing the magnitude of tremor. The decrease in tremor produced by metoprolol (47, sem 9%, n = 23) was not significantly different from that observed propranolol (55, sem 5%, n = 23). Tachycardia on standing was antagonised by both drugs to a similar extent. These findings suggest that metoprolol may represent a valuable alternative to propranolol in the treatment of essential tremor. The data is consistent with the hypothesis that the tremorolytic effect of beta blockers in these patients may be unrelated to peripheral beta-2 adreno-receptor blockade, being possibly mediated by other central or peripheral modes of action of these drugs. However, it cannot be excluded that at the dose used, metoprolol had lost its relative cardio-selectivity and that the reduction in tremor was mediated by competitive antagonism at beta-2 receptor sites in skeletal muscle.

Cardioselectivity of atenolol in asthmatic patients

This double-blind, randomised, within patient, placebo-controlled study set out to investigate the effect of a cardioselective beta-blocker, atenolol, at different oral doses (50, 100 and 200 mg) and a non-selective agent, propranolol (40 mg), upon 1. airways resistance (forced expiratory volume at one second = FEV1) and 2. the bronchodilator action of increasing doses of inhaled isoprenaline, in patients with co-existent hypertension and reversible airways obstruction. In 10 patients, two hours after drug administration, the 3 doses of atenolol caused a significantly greater (P less than 0.05) degree of B1-blockade than propranolol. In contrast the 3 doses of atenolol caused significantly less (P less than 0.05 to 0.01) B2-blockade as evidenced by a smaller fall in FEV1. The isoprenaline FEV1 dose response curves were displaced progressively to the right of the placebo curve with increasing doses of atenolol, but the greatest displacement was with propranolol. It was concluded that patients with reversible airways obstruction who require beta-blockade should be given a low dose of a cardioselective agent in conjunction with, if required, a beta 2 stimulant such as isoprenaline. Such a treatment will be less likely to cause a troublesome increase in airways resistance and the bronchodilator action of the beta 2 stimulant will be almost fully preserved.

Cardiovascular effects of single oral doses of the new beta-adrenoceptor blocking agents betaxolol (SL 75212) in healthy volunteers

1 The effects of betaxolol (SL 75212), a new beta-adrenoceptor blocking agent, on the cardiovascular response to exercise have been studied in six normal subjects after placebo and single oral doses of 5, 10, 20 and 40 mg given double-blind in a randomized sequence. 2 All doses reduced exercise heart rate, with a significant reduction persisting to 23 h after doses of 20 mg and 40 mg. Systolic blood pressure on exercise was reduced after all doses, with a reduction continuing to 23 h after doses of 10 mg and above. 3 The mean elimination half-life of SL 75212 was 17.5 +/- 3.9 h. The plasma clearance ranged from 0.15--0.48 1 kg-1 h-1 and the volume of distribution from 5.8--13 1 kg-1. 4 There was a significant correlation between the peak blood levels and change in exercise heart rate (r = 0.53, P less than 0.05) and between the area under the blood concentration curve and the effect of the exercise heart rate (r = 0.55, P less than 0.01).

Beta-blockers and asthma

In a single-blind, randomised, crossover study in 10 asthmatic patients, the effects of approximately equipotent oral doses of 3 cardioselective beta-blockers-atenolol (100 mg), metoprolol (100 mg), and acebutolol (300 mg)-and 4 non-cardioselective beta-blockers-proranolol (100 mg), oxprenolol (100 mg), pindolol (5 mg), and timolol (10 mg) upon FEV1 were compared. All drugs, except pindolol, produced a significant reduction in standing pulse rate and prevented an increase in heart rate after inhaled isoprenaline (1500 microgram). All drugs caused a fall in FEV1 but only atenolol did not differ significantly from placebo in this respect. The bronchodilator response to inhaled isoprenaline was blocked by the 4 non-cardioselective drugs; the 3 cardioselective agents permitted some bronchodilatation, but only atenolol did not differ from placebo.

Comparative trial of propranolol and practolol in hyperthyroidism

The possible role of practolol in the management of hyperthyroidism has been studied by comparing it with propranolol. 2. In a double-blind cross-over trial, propranolol (40 mg), practolol (120 mg) and a placebo four times daily for one week were compared in twenty-one hyperthyroid patients by sequential analysis. 3. Judged by their effect on the symptoms and signs of thyrotoxicosis, both propranolol and practolol were significantly better than the placebo but no clear distinction could be made between the two active compounds. 4. Propranolol and practolol reduced heart rate by 24 and 17% respectively compared with placebo. 5. Patients generally preferred propranolol or practolol to placebo but this preference did not achieve significance with either drug. 6. Only in its effect on heart rate was practolol significantly inferior to propranolol, and it would appear to be a useful alternative to propranolol in the management of the peripheral manifestations of hyperthyroidism.