CNS Pharmacology USMLE Step 1 Practice Question

A 27-year-old woman at 9 weeks of gestation presents to her obstetrician complaining of a 6-week history of heat intolerance, fine resting tremor, unintentional weight loss of 8 pounds, and palpitations. Her temperature is 37.8°C, blood pressure is 138/82 mmHg, heart rate is 112 beats/min, and respiratory rate is 18 breaths/min. Physical examination reveals warm, moist skin, a diffusely enlarged nontender thyroid gland, and a fine tremor of the outstretched hands. Ophthalmologic examination shows mild lid lag bilaterally. Laboratory testing demonstrates a suppressed TSH of 0.01 mIU/L and an elevated free T4 of 3.8 ng/dL. Concerned about the risks of methimazole embryopathy during the first trimester, her physician instead initiates a medication that inhibits thyroid peroxidase and additionally blocks peripheral conversion of T4 to the more active T3. Which of the following drugs was most likely prescribed?