Which medication is used to inhibit peripheral conversion of T4 to T3 in thyroid storm?

Which medication is used to inhibit peripheral conversion of T4 to T3 in thyroid storm?

• A. PTU
• B. Methimazole
• C. Levothyroxine
• D. Propranolol

Answer: (A)

In thyroid storm, rapidly reducing the active thyroid hormone effect is crucial, and one key way is to lower the amount of T3 produced from T4 in peripheral tissues. Propylthiouracil does this by two actions: it inhibits thyroid peroxidase, which stops new hormone synthesis, and it also blocks the 5'-deiodinase enzyme that converts T4 to the more active T3 outside the thyroid. This combination leads to a quicker drop in T3 levels, which helps stabilize the patient faster. Methimazole likewise blocks thyroid hormone synthesis by inhibiting thyroid peroxidase, but it does not significantly affect peripheral conversion, so its impact on T3 levels is less immediate. Levothyroxine would add more thyroid hormone, worsening the situation. Propranolol helps control sympathetic symptoms and can modestly reduce T4 to T3 conversion, but its primary use in storm is symptomatic management, not the main tool for lowering peripheral conversion. Thus, the drug best used to inhibit peripheral conversion of T4 to T3 in thyroid storm is propylthiouracil.

In thyroid storm, rapidly reducing the active thyroid hormone effect is crucial, and one key way is to lower the amount of T3 produced from T4 in peripheral tissues. Propylthiouracil does this by two actions: it inhibits thyroid peroxidase, which stops new hormone synthesis, and it also blocks the 5'-deiodinase enzyme that converts T4 to the more active T3 outside the thyroid. This combination leads to a quicker drop in T3 levels, which helps stabilize the patient faster.

Methimazole likewise blocks thyroid hormone synthesis by inhibiting thyroid peroxidase, but it does not significantly affect peripheral conversion, so its impact on T3 levels is less immediate. Levothyroxine would add more thyroid hormone, worsening the situation. Propranolol helps control sympathetic symptoms and can modestly reduce T4 to T3 conversion, but its primary use in storm is symptomatic management, not the main tool for lowering peripheral conversion. Thus, the drug best used to inhibit peripheral conversion of T4 to T3 in thyroid storm is propylthiouracil.