In thyroid storm management, why is iodine given after a thionamide?

• A. To prevent iodine uptake by the thyroid
• B. To increase iodine uptake
• C. To block release of thyroid hormones after synthesis is inhibited
• D. To enhance synthesis of thyroid hormones

Answer: (C)

The key idea is using two drugs in a specific sequence to rapidly curb thyroid hormone activity in a thyroid storm. A thionamide blocks the thyroid’s ability to make new T3 and T4 by inhibiting thyroid peroxidase, so synthesis is shut down. Giving a large dose of iodine after this block takes advantage of the iodine load to stop the release of whatever preformed hormone remains and to suppress further release—this is the acute iodine effect (Wolff-Chaikoff effect). If iodine were given first, it could be used for synthesis before the thionamide can block it, potentially worsening thyrotoxicosis. So the purpose of giving iodine after the thionamide is to prevent release of hormones after synthesis has been inhibited.