The effect of benziodarone on the thyroid hormone levels and the pituitary-thyroid axis

The effect of benziodarone on the levels of thyroid hormones in the serum has not attracted interest, in spite of the prolific literature on the related drug amiodarone. It is shown here that benziodarone administration has several effects, mainly similar to amiodarone, but some possibly opposite and inappropriate. Nine normal volunteers received benziodarone, 100 mg three times daily for 14 days. Before and 1, 3, 7 and 14 days after continuous administration the following estimates were obtained: serum T4, T3, rT3 and TSH, both basal (TSH0) and 30 min after iv administration of TRH (TSH30), the difference being calculated as delta TSH. Serum T4 remained relatively constant. Serum T3 decreased significantly from the 1st to the 14th day (eg. before 2.15 +/- 0.12 nmol/l, at 3 days 1.45 +/- 0.07). Serum rT3 increased significantly from the 1st to the 14th day (eg. before 0.71 +/- 0.16 nmol/l, at 7 days 2.61 +/- 0.19). Serum TSH0 and TSH30 decreased significantly on the 1st and 3rd day. Later they increased, and TSH0 at 14 days was significantly higher than the pre-treatment value. Our results suggest that benziodarone has an amiodarone-like action in diverting the peripheral metabolism of T4 towards rT3 rather than T3. However, the effects on the pituitary-thyroid axis are not similar to those previously reported by others and ourselves about amiodarone, and these merit further research.