Background: Many patients receiving amiodarone therapy are male. The long-term risk for amiodarone-induced thyroid dysfunction in these patients has not been systematically and prospectively investigated. The purpose of this study was to determine the extent of amiodarone-induced thyroid dysfunction in a large male cohort.

Methods: This is a substudy of a prospective randomized controlled trial (SAFE-Trial) in which amiodarone, sotalol, and placebo for persistent atrial fibrillation were evaluated. For the purpose of this substudy, sotalol and placebo groups were combined into a control group. Serial thyroid function tests were performed over 1-4.5 years. Of the 665 patients enrolled in the SAFE-Trial, 612 patients were included in this sub-study.

Results: Subclinical hypothyroidism, thyroid-stimulating hormone (TSH) level 4.5-10 mU/L, was seen among 25.8% of the amiodarone-treated patients and only 6.6% of controls (P <.0001). Overt hypothyroidism, TSH level >10 mU/L, was seen among 5.0% of the amiodarone-treated patients, and only 0.3% of controls (P <.001). By 6 months, 93.8% of the patients who developed TSH elevations above 10 mU/L on amiodarone had been detected. There was a trend toward a greater proportion of hyperthyroidism, defined as a TSH <0.35 mU/L, in the amiodarone group compared with the control group (5.3% vs 2.4%, P=.07).

Conclusions: Hypothyroidism developed in 30.8% of older males treated with amiodarone and in only 6.9% of the controls. Hypothyroidism presented at an early stage of therapy. Hyperthyroidism occurred in 5.3% of amiodarone treated patients, and was a subclinical entity in all but 1 case.