Drugs in 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.

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Pharmacology · Drugs in pregnancy: antithyroid drugs

Sample item

A woman at 7 weeks of gestation has newly diagnosed Graves disease with a heart rate of 112 per minute. Which treatment plan is most appropriate?

AMethimazole throughout the whole pregnancyBRadioactive iodine as soon as possibleCPropylthiouracil throughout pregnancy and breastfeeding with no changeDPropylthiouracil in the first trimester, then consider a switch to methimazole

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

The answer and the reasoning

D. Propylthiouracil in the first trimester, then consider a switch to methimazole

Methimazole and carbimazole are linked to an embryopathy (aplasia cutis, choanal atresia, oesophageal atresia) during early organogenesis, so propylthiouracil is preferred in the first trimester. PTU carries a risk of severe hepatotoxicity, so many guidelines advise switching to methimazole after the first trimester. Radioactive iodine is contraindicated because it destroys the fetal thyroid.

Option by option

A. Methimazole throughout the whole pregnancy
Methimazole in the first trimester risks embryopathy.
B. Radioactive iodine as soon as possible
Radioactive iodine crosses the placenta and ablates the fetal thyroid.
C. Propylthiouracil throughout pregnancy and breastfeeding with no change
Prolonged PTU use without review exposes the mother to hepatotoxicity.
D. Propylthiouracil in the first trimester, then consider a switch to methimazole (correct)
Correct. This plan avoids early methimazole teratogenicity and prolonged PTU liver risk.

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, Propylthiouracil in the first trimester, then consider a switch to methimazole. Methimazole and carbimazole are linked to an embryopathy (aplasia cutis, choanal atresia, oesophageal atresia) during early organogenesis, so propylthiouracil is preferred in the first trimester.

Why is "Methimazole throughout the whole pregnancy" not the answer?

Methimazole in the first trimester risks embryopathy.

Why is "Radioactive iodine as soon as possible" not the answer?

Radioactive iodine crosses the placenta and ablates the fetal thyroid.

Why is "Propylthiouracil throughout pregnancy and breastfeeding with no change" not the answer?

Prolonged PTU use without review exposes the mother to hepatotoxicity.

What concept does this question test?

It tests Drugs in pregnancy: antithyroid drugs in Pharmacology. PTU carries a risk of severe hepatotoxicity, so many guidelines advise switching to methimazole after the first trimester. Radioactive iodine is contraindicated because it destroys 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 Drugs in 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.