Acute Effects of Amiodarone Administration on Thyroid Function in Patients with Cardiac Arrhythmia

Because little has been published on early effects of treatment with amiodarone on thyroid function, we studied serum total and free thyroid hormone, reverse T3, and TSH levels in patients with cardiac arrhythmias during the first 10 days of treatment with a loading dose of amiodarone by iv infusion. Twenty-four patients were enrolled in the study. A standardized loading regimen for the iv infusion of amiodarone was used. The protocol provided the iv infusion of 20 mg/kg per day on day 1, the iv infusion of 10 mg/kg per day on day 2, then 600 mg/day per os for 7–10 days, and finally, in patients chronically treated with the drug, the dose was gradually reduced to 400–200 mg/day per os. Total and free concentrations of T4 tended to progressively and significantly increase (P < 0.0001 repeated measures ANOVA) starting from the fourth day of therapy, whereas total T3 decreased from the second day progressively (P < 0.0001) throughout the study; free T3 did not significantly change. TSH levels early and signi...