In thyroid storm management, which drug is used to rapidly reduce peripheral conversion of T4 to T3?

In thyroid storm management, which drug is used to rapidly reduce peripheral conversion of T4 to T3?

• A. Methimazole
• B. Propylthiouracil
• C. Lugol's iodine
• D. Radioactive iodine

Answer: (B)

In thyroid storm, rapidly lowering the active hormone T3 is crucial, and Propylthiouracil achieves this best because it blocks the enzyme that converts T4 to T3 in peripheral tissues. By inhibiting 5'-deiodinase, Propylthiouracil prevents the conversion of circulating T4 into the more active T3, so T3 levels fall quickly. It also inhibits thyroid peroxidase, reducing new hormone synthesis, giving a dual action for fast control. Methimazole also blocks hormone synthesis but doesn’t significantly inhibit deiodination, so it doesn’t produce as rapid a drop in T3. Lugol's iodine helps reduce hormone release acutely but doesn’t affect peripheral conversion, and radioactive iodine isn’t used for immediate control. So the rapid reduction of T4 to T3 is best achieved with Propylthiouracil.

In thyroid storm, rapidly lowering the active hormone T3 is crucial, and Propylthiouracil achieves this best because it blocks the enzyme that converts T4 to T3 in peripheral tissues. By inhibiting 5'-deiodinase, Propylthiouracil prevents the conversion of circulating T4 into the more active T3, so T3 levels fall quickly. It also inhibits thyroid peroxidase, reducing new hormone synthesis, giving a dual action for fast control. Methimazole also blocks hormone synthesis but doesn’t significantly inhibit deiodination, so it doesn’t produce as rapid a drop in T3. Lugol's iodine helps reduce hormone release acutely but doesn’t affect peripheral conversion, and radioactive iodine isn’t used for immediate control. So the rapid reduction of T4 to T3 is best achieved with Propylthiouracil.