Comparison of propranolol and carbimazole as adjuncts to iodine-131 therapy of hyperthyroidism

Abstract

Abstract. Seventy thyrotoxic patients were treated with carbimazole (36 patients) or propranolol (34 patients) prior to and for 6 weeks after a therapeutic dose of 131I. The therapeutic response was evaluated on the basis of the serum free thyroxine index (FT4I) value and the thyrotoxicosis therapy-index (TTI) of Crooks et al. (1960b). Propranolol alleviated many symptoms and signs (palpitations, hyperkinesia, finger tremor, resting pulse rate) as effectively as carbimazole, whereas others (dyspnoea on effort, tiredness, heat intolerance, sweating, nervousness, bodyweight) were not equally affected. Biochemical euthyroidism was achieved significantly slower in the propranolol group (after 100.6 ± 40.5 days vs. 48.5 ± 24.0 days in the carbimazole group) although the dose of 131I was administered after a mean interval of 22 days from the start of treatment in the propranolol group and after 66 days in the carbimazole group. Between 2 and 6 months after 131I the FT4I and TTI followed a similar course in both treatment groups. As judged from the TTI scores 2 weeks after the 131I-therapy no evident aggravation of hyperthyroidism occurred in either group of patients. However, one patient in each group showed marked exacerbation of symptoms which was due to inadequate dosage of the drugs. It is concluded that propranolol, given prior to radioactive iodine, is equally effective as carbimazole in preventing aggravation of thyrotoxicosis after the administration of 131I. In the propranolol-treated patients the tests of thyroid function are more reliable during the drug therapy, but the slow development of euthyroidism may be of clinical importance in patients presenting with severe symptoms.