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October 1977

Propranolol Hydrochloride for Thyrotoxicosis

Arch Intern Med. 1977;137(10):1485. doi:10.1001/archinte.1977.03630220109030

To the Editor.—  The use of propranolol hydrochloride as the only drug for treating thyrotoxicosis was discussed in a recent article by Mazzaferri et al (Archives 136:50-56, 1976) and in a subsequent letter by Biran (Archives 136:1197, 1976). Mazzaferri indicated that propranolol, although not as a first choice drug, could be given with benefit at least in some cases, whereas Biran has seriously questioned its use on the grounds of the "known lack of specific effects of propranolol on the metabolism of thyroid gland...." This is not unquestionably true, since in vitro experiments have demonstrated that adrenergic mechanisms are involved in human1 and animal2 thyroid hormone secretions and are influenced by propranolol. However, the beneficial effects of propranolol in thyrotoxicosis may result from its effect on the peripheral metabolism of thyroid hormones. In fact, we demonstrated by radioimmunoassay measurements that therapeutic doses of propranolol hydrochloride (120 mg/ day)