Which antidysrhythmic drug can cause hypothyroidism or hyperthyroidism?

Which antidysrhythmic drug can cause hypothyroidism or hyperthyroidism?

• A. Amiodarone
• B. Verapamil
• C. Phenytoin
• D. Lidocaine

Answer: (A)

Amiodarone is the antidysrhythmic most likely to affect the thyroid because it contains a very large amount of iodine and has direct effects on thyroid hormone synthesis and metabolism. The excess iodine can trigger two different pathways: it can cause hypothyroidism in some individuals through the Wolff-Chaikoff effect, where the thyroid temporarily silences hormone production in the face of a large iodine load; or it can cause hyperthyroidism in others, either by promoting autonomous thyroid tissue to make more hormone (iodine-induced hyperthyroidism) or by causing a destructive thyroiditis that releases stored hormone. Because of these dual possibilities, amiodarone can lead to either hypo- or hyperthyroidism, making thyroid function monitoring essential during treatment. Verapamil and lidocaine don’t have this thyroid-disrupting effect, while phenytoin can influence thyroid hormones through liver enzyme induction but is not the classic cause of amiodarone-like thyroid dysfunction.

Amiodarone is the antidysrhythmic most likely to affect the thyroid because it contains a very large amount of iodine and has direct effects on thyroid hormone synthesis and metabolism. The excess iodine can trigger two different pathways: it can cause hypothyroidism in some individuals through the Wolff-Chaikoff effect, where the thyroid temporarily silences hormone production in the face of a large iodine load; or it can cause hyperthyroidism in others, either by promoting autonomous thyroid tissue to make more hormone (iodine-induced hyperthyroidism) or by causing a destructive thyroiditis that releases stored hormone. Because of these dual possibilities, amiodarone can lead to either hypo- or hyperthyroidism, making thyroid function monitoring essential during treatment. Verapamil and lidocaine don’t have this thyroid-disrupting effect, while phenytoin can influence thyroid hormones through liver enzyme induction but is not the classic cause of amiodarone-like thyroid dysfunction.