Effects of amiodarone therapy on thyroid function

Abstract

Amiodarone is a benzofuran derivative approved for the treatment of cardiac arrhythmias. Traditionally classified as a class III antiarrhythmic agent, amiodarone possesses electrophysiologic properties of all four Vaughan-Williams classes. This drug, however, has high iodine content, and this feature plus the intrinsic effects on the body make amiodarone especially toxic to the thyroid gland. Treatment can result in a range of effects from mild derangements in thyroid function to overt hypothyroidism or thyrotoxicosis. The diagnosis and treatment of amiodarone-induced hypothyroidism is usually straightforward, whereas that of amiodarone-induced thyrotoxicosis and the ability to distinguish between the type 1 and type 2 forms of the disease are much more challenging. Dronedarone was approved in 2009 for the treatment of patients with atrial fibrillation. As amiodarone, dronedarone is a benzofuran derivative with similar electrophysiologic properties. In contrast to amiodarone, however, dronedarone is structurally devoid of iodine and has a notably shorter half-life. In studies reported before FDA approval, dronedarone proved to be associated with significantly fewer adverse effects than amiodarone, making it a more attractive choice for patients with atrial fibrillation or flutter, who are at risk of developing amiodarone-induced thyroid dysfunction.

Amiodaron i tarczyca

“…Nadczynność tarczycy indukowana AMIO występuje 3-krotnie częściej u mężczyzn niż u kobiet [31]. NadTabela I. Zmiany stężeń hormonów tarczycowych u pacjentów w eutyreozie podczas terapii AMIO Układ sercowo-naczyniowy < 10% Bradykardia (5%), wydłużenie QT, bloki serca, rzadko (< 1%) torsades de pointes…”

“…Przebieg taki może wynikać z fizjologicznego działania AMIO, takiego jak: antagonistyczny efekt na receptory b-adrenergiczne, hamowanie dejodynacji T4 do T3, blokada wiązania hormonów tarczycowych do receptora T3 w sercu. -z drugiej strony, AIT może charakteryzować się bardzo ciężkim przebiegiem, szczególnie u osób młodych, u których kliniczna manifestacja jest identyczna jak w przypadku spontanicznej nadczynności tarczycy [25,31,42].…”

“…AIT has a higher male-to-female ratio of 3:1 [31]. AIT usually develops after months of AMIO treatment, but it can develop in the first few weeks of therapy [32].…”

“…An asymptomatic course of AIT may be the reason for misdiagnosis. This may be related to physiological AMIO actions, such as: antagonist effect on b-adrenergic receptors, inhibition of deiodination T4 to the metabolically active T3, and blockade of thyroid hormone binding to T3 receptors in the heart; -on the other hand, AIT may also be heavily symptomatic, especially in younger patients whose clinical manifestations are indistinguishable from those of spontaneous hyperthyroidism [25,31,42].…”

The difficult patient: drug interaction and the influence of concomitant diseases on the treatment of hypothyroidism

“…Interestingly, some agents, such as amiodarone and iodide may cause both hypo-and hyperthyroidism (53,54). Amiodarone is a drug very frequently used in Brazil.…”