Pregnancy: antithyroid drugs: practice question

A Pharmacology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

Try it

Pharmacology · Pregnancy: antithyroid drugs

Sample item

A woman at 8 weeks of gestation with Graves disease is on methimazole, still needs treatment and has a free T4 at the upper limit. What is the best change in her management?

AContinue methimazole at the same doseBIncrease the methimazole dose to bring free T4 to the lower reference rangeCGive radioactive iodine ablation nowDSwitch to propylthiouracil for the first trimester

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Switch to propylthiouracil for the first trimester

Methimazole (carbimazole) in early pregnancy is associated with aplasia cutis, choanal atresia and other embryopathy, so propylthiouracil is preferred during organogenesis. Because of rare severe hepatotoxicity, many switch back to methimazole after the first trimester. Radioiodine is contraindicated since it ablates the fetal thyroid.

Option by option

A. Continue methimazole at the same dose
Continuing methimazole exposes the embryo to its teratogenic risk during organogenesis.
B. Increase the methimazole dose to bring free T4 to the lower reference range
Higher methimazole exposure raises teratogenic risk, and the target is the upper reference range.
C. Give radioactive iodine ablation now
Radioiodine is contraindicated in pregnancy and destroys the fetal thyroid after 10 weeks.
D. Switch to propylthiouracil for the first trimester (correct)
Correct. Propylthiouracil is the safer antithyroid drug in the first trimester.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is D, Switch to propylthiouracil for the first trimester. Methimazole (carbimazole) in early pregnancy is associated with aplasia cutis, choanal atresia and other embryopathy, so propylthiouracil is preferred during organogenesis.

Why is "Continue methimazole at the same dose" not the answer?

Continuing methimazole exposes the embryo to its teratogenic risk during organogenesis.

Why is "Increase the methimazole dose to bring free T4 to the lower reference…" not the answer?

Higher methimazole exposure raises teratogenic risk, and the target is the upper reference range.

Why is "Give radioactive iodine ablation now" not the answer?

Radioiodine is contraindicated in pregnancy and destroys the fetal thyroid after 10 weeks.

What concept does this question test?

It tests Pregnancy: antithyroid drugs in Pharmacology. Because of rare severe hepatotoxicity, many switch back to methimazole after the first trimester. Radioiodine is contraindicated since it ablates the fetal thyroid.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Pregnancy: antithyroid drugs?

Learn drugs as classes, then the exception in each class that an examiner would pick. Then use the flashcards and the other Pharmacology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.