Failure of Methimazole to Affect Peripheral Thyroid Indices in Man ∗

Abstract

Summary and Conclusions

The effects of methimazole (60 mg/day) on peripheral thyroxine turnover and transport were investigated in 16 adult volunteers. In four subjects (two euthyroid individuals and two myxedematous patients in the euthyroid state on thyroxine replacement) using exogenously administered ¹³¹I-labeled L-thyroxine, the radiothyroxine turnover was investigated. Simultaneously, the effects of methimazole administration (10 days) on thyroxine-binding serum protein carriers (11 subjects) and serum free-thyroxine levels (six subjects) were observed. Methimazole administration in man in these studies was shown to have no effect on peripheral thyroid indices: thyroxine binding to serum proteins, the serum free-thyroxine levels or the turnover and total quantitative degradation of thyroxine. This finding confirms a similar result on thyroxine turnover in one myxedematous patient reported earlier 2 .

From the present data it would appeax that methimazole does not alter the turnover, transport or quantitative degradation of thy-roxine in man when compared to pmpyl-thiouracil.