Which medication from the thyroid storm management group is an antithyroid drug?

• A. Propranolol
• B. Methimazole
• C. Lithium carbonate
• D. Hydrocortisone

Answer: (B)

In thyroid storm, you want to rapidly stop new thyroid hormone from being made. The antithyroid drugs, also called thionamides, block thyroid hormone synthesis by inhibiting thyroid peroxidase, which prevents iodination and coupling that form T3 and T4. Methimazole is a thionamide, so it directly reduces production of thyroid hormones and is the antithyroid drug in this group.

Propranolol helps control the adrenergic symptoms and can modestly reduce peripheral conversion of T4 to T3, but it doesn’t stop hormone synthesis. Hydrocortisone treats potential adrenal insufficiency and also helps lower T4 to T3 conversion, but is not an antithyroid. Lithium carbonate can inhibit release of thyroid hormone but isn’t an antithyroid drug.