The ASSESSMENT OF Β‐ADRENOCEPTOR BLOCKING DRUGS IN HYPERTHYROIDISM

Abstract

Intravenous propranolol and practolol both reduced resting supine heart rate in patients with hyperthyroidism. Propranolol produced a significantly greater reduction than practolol, which did not have a dose-dependent effect. 2 The effect of these drugs on resting heart rate was much less than their effect on the tachycardias produced both by severe exercise and by standing upright in hyperthyroid patients. Propranolol again produced a significantly greater reduction than practolol in each situation, but practolol did have a dose dependent effect on exercise heart rate. 3 The percentage reduction of standing tachycardia produced by the two drugs appeared to parallel closely the reduction in exercise tachycardia. 4 It is concluded that a simple and convenient way of assessing the activity of ,B-adrenoceptor blocking drugs in hyperthyroid patients would be to measure their effect on the tachycardia induced by standing. Their effect on resting heart rate should not be used. 5Practolol may be useful in the management of hyperthyroidism in patients in whom propranolol and similar non-selective j-adrenoceptor blocking drugs are contraindicated.

Beta-blockers and asthma.

“…Though suppression of the tachycardia associated with severe exercise (where there is little or no vagal influence) is the ideal way of assessing betablockade, some investigators have found that standing produces an assessment of beta-blockade not dissimilar from that obtained by more elaborate methods, i.e. severe exercise (Carruthers et al, 1974;Kofi Ekue et al, 1974). Moreover, such a simple method is easy to use in outpatient clinics-as in the present study.…”

Comparative trial of propranolol and practolol in hyperthyroidism.

“…Recently, however, Carruthers, Ghosal, McDevitt, Nelson & Shanks (1974) demonstrated that practolol did have a dose-dependent effect in hyperthyroid patients on the tachycardia induced by severe excercise, an accepted method for demonstrating the effectiveness of,-adrenoceptor blocking drugs (Brick, Hutchison, McDevitt, Roddie & Shanks, 1968;Coltart & Shand, 1970 Three preferences were thus determinedpatient's subjective preference, observer's objective preference without heart rate and observer's preference including heart rate -for each comparison (propranolol and placebo, practolol and placebo, and propranolol and practolol) and these were submitted to sequential analysis using the method described by Armitage (1960).…”

Propranolol Dosage in Thyrotoxicosis

“…Although the effect of propranolol on resting heart rate has been used in a number of studies (3,10,13), this does not give a reliable index of the drug's effect in hyperthyroidism (13).…”

“…Some thyrotoxic patients, however, have heart rates at this level before therapy; thus, the use of absolute resting heart rate (3,10) gives no indication of patient drug compliance, and in other patients with severe thyrotoxicosis it may not be possible to reduce the pulse rate to this level, as the intrinsic heart rate (after pharmacological denervation) is increased in thyrotoxic patients (21). In addition, resting heart rates do not give a reliable index of /?-adrenergic blockade in thyrotoxic patients (13), and thyroid storm has been described (11,12) in patients with resting pulse rates of less than 90 beats/min.…”

“…The degree of /?-adrenergic blockade brought about by propranolol was assessed electrocardiographically from the reduction in tachycardia induced by step exercise (13). Before therapy, patients were exercised on a step; the height of the step, rate, and duration of exercise was individually determined to make the exercise as severe as patients could tolerate and to produce a heart rate of greater than 140/min in each patient.…”