Endocrine pharmacotherapy · USMLE Step 1

A patient is prescribed propylthiouracil (PTU). Which mechanism distinguishes PTU from methimazole?

  1. Inhibition of thyroid peroxidase
  2. Inhibition of peripheral T4-to-T3 conversion
  3. Blocking iodine uptake
  4. Destruction of thyroid tissue
Show answer and explanation

Correct answer: Inhibition of peripheral T4-to-T3 conversion

PTU inhibits both thyroid peroxidase and peripheral T4-to-T3 conversion; methimazole inhibits only the former.

Difficulty: Medium Question 12 of 20

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