Sunday, February 10, 2019

Amiodarone and thyroid dysfunction

Amiodarone, a class III antiarrhythmic drug is associated with a number of side effects, including thyroid dysfunction (both hypo- and hyperthyroidism)

There are two types of amiodarone-induced thyrotoxicosis (AIT):
Type I: This type is typically seen in patients with preexisting multinodular goiter or latent Graves disease, the excess iodine from amIODarone results in enhanced thyroid hormone production.

Type II: In type II AIT there is destructive thyroiditis caused by the drug itself that results in excess release of T4 and T3(There is no hormone production). It typically occurs in patients without underlying thyroid disease.

1)Normally after exposure to an iodine load (eg, radiocontrast), iodine transport and thyroid hormone synthesis are transiently inhibited to prevent normal individuals from becoming hyperthyroid(the Wolff-Chaikoff effect). Normally patients escape this Wolff-Chaikoff effect and come back to normal within a few weeks, but patients with pre-existing subclinical thyroid disease fail to escape and develop hypothyroidism.

2)Amiodarone also inhibits 5'-deiodinase which is responsible for the peripheral conversion of T4 to T3. So there is a decrease in T3 production.

-Srikar Sama

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