Effects of amiodarone on thyroid function in patients with ischaemic heart disease

Thyroid function was evaluated clinically and biochemically in 12 patients with ischaemic heart disease receiving 200 mg oral amiodarone three times daily for periods up to 6 weeks. During drug administration, no patient developed clinical or laboratory evidence of hypothyroidism, but serum levels of T3 tended to fall and those of T4 increased but not to levels outside the normal range. Amiodarone produced a significant reduction in heart rate with prolongation of the QTc interval of the electrocardiogram without altering either the PR interval or the QRS duration. These effects of the drug were still present 4 weeks after cessation of treatment. In spite of the high iodine content, amiodarone does not, therefore, depress thyroid function to any important degree during chronic administration and its antianginal action does not appear to be caused by the production of generalized hypothyroidism.