The assessment of β-adrenoceptor blocking drugs in hyperthyroidism.

1 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 β-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. 5 Practolol may be useful in the management of hyperthyroidism in patients in whom propranolol and similar non-selective β-adrenoceptor blocking drugs are contraindicated.