benzofurans and Thyrotoxicosis

Amiodarone and dronedarone are two clinically important benzofuran derivatives. Amiodarone has been used widely for treating resistant tachyarrhythmias in the past three decades. However amiodarone and its main metabolically active metabolite desethylamiodarone can adversely affect many organs, including the thyroid gland. Amiodarone-induced thyroid disorders are common and often present as a management challenge for endocrinologists. The pathogenesis of amiodarone-induced thyroid dysfunction is complex but the inherent effects of the drug itself as well as its high iodine content appear to play a central role. The non-iodinated dronedarone also exhibits anti-arrhythmic properties but appears to be less toxic to the thyroid. This review describes the biochemistry of benzofuran derivatives, including their pharmacology and the physiology necessary for understanding the cellular mechanisms involved in their actions. The known effects of these compounds on thyroid action are described. Recommendations for management of amiodarone-induced hypothyroidism and thyrotoxicosis are suggested. Dronedarone appears to be an alternative but less-effective anti-arrhythmic agent and it does not have adverse effects on thyroid function. It may have a future role as an alternative agent in patients being considered for amiodarone therapy especially those at high risk of developing thyroid dysfunction but not in severe heart failure.

Topics: Amiodarone; Animals; Anti-Arrhythmia Agents; Benzofurans; Dronedarone; Humans; Hypothyroidism; Receptors, Thyroid Hormone; Thyroid Diseases; Thyroid Gland; Thyrotoxicosis

Drug-induced thyrotoxicosis is not uncommon. It may worsen life-threatening arrhythmias and may be refractory to medical treatment. Near-total thyroidectomy presents a valid alternative to medical therapy and should be considered early in the management of the disease.. To assess whether near-total thyroidectomy was a viable approach for our patients.. Twelve patients--7 men and 5 women, aged 63 to 82 years--presented with drug-induced fulminant thyrotoxicosis following 1 to 12 months of amiodarone treatment (11 patients, mean 7 months) and after a 6 months course of interferon-alpha treatment (one patient). Medical therapy included propylthiouracil in doses up to 1200 mg/day in all patients and a beta-receptor antagonist in seven. Five patients had to stop amiodarone treatment and start high doses of steroids. A thyroid scan was performed in all patients using 5 mCi of Tc-99m pertechnetate. The thyroid scan showed absent uptake of the tracer in the thyroid bed in all patients, precluding the use of radioablation.. Four patients (three with AIT and one with interferon therapy) who did not respond to 3 months of medical therapy required surgical thyroidectomy due to severe unremitting thyrotoxicosis. A near-total thyroidectomy resulted in rapid correction of thyrotoxicosis, enabling continuation of the anti-arrhythmic drug. There were no intraoperative or postoperative arrhythmias. Subsequently, all patients recovered rapidly and remained well and euthyroid on thyroxine replacement therapy.. Since surgery results in rapid control of thyrotoxicosis and permits continued therapy with amiodarone, we suggest that near-total thyroidectomy warrants consideration as a definitive treatment for resistant amiodarone or interferon-induced thyrotoxicosis.

Topics: Aged; Aged, 80 and over; Amiodarone; Angiogenesis Inhibitors; Anti-Arrhythmia Agents; Benzofurans; Female; Humans; Interferon-alpha; Male; Middle Aged; Risk Factors; Thyroidectomy; Thyrotoxicosis