The effect of long-term amiodarone therapy of thyroid function with a low-dose approach

We evaluated 101 patients treated with low-dose amiodarone over a ten-year period in order to assess the incidence of thyroid dysfunction and to identify the factors, which may predict the development of thyroid dysfunction. The cohort was treated with an average oral loading of 670±102 mg/day and maintenance of 275±102 mg/day. Thyroid dysfunction, assessed by T3, T4 and TSH developed in fifteen patients (14.8%). Of those, eight had hypothyroidism (7.9%) and seven hyperthyroidism (6.9%). No statistically significant differences were found between euthyroid patients and those with hyroid dysfunction with respect to age, gender, weight, amiodarone and desethyl (D-E) amiodarone levels, total amiodarone levels, total amiodarone dose or duration of therapy (P=NS). On the average, hypothyroidism developed after 15±10 months of treatment, while hyperthyroidism developed after 41.7±13.2 months. This resulted in a difference in the total dose of amiodarone received until development of either hyperthyroidism or hypothyroidism, 147±112g for hypothyroid patients and of 284±97g for hyperthyroid patients (P=0.02). All cases of clinical hyperthyroidism were transient and responded to dose reductions of amiodarone. Changes in the biochemical abnormalities of either hypothyroidism and hyperthyroidism occurred after two months of therapy on a lower dose of amiodarone.