Thyroid drugs: propylthiouracil: 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 · Thyroid drugs: propylthiouracil

Sample item

Which additional action distinguishes propylthiouracil from methimazole?

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

The answer and the reasoning

D. It inhibits peripheral conversion of T4 to T3

Both thionamides inhibit thyroid peroxidase, but propylthiouracil also inhibits 5'-deiodinase, reducing T4-to-T3 conversion. This is useful in thyroid storm, though hepatotoxicity limits routine use.

Option by option

  • A. It replaces thyroid hormone

    Levothyroxine replaces thyroid hormone.

  • B. It destroys thyroid follicles with beta radiation

    Radioiodine causes beta-radiation-mediated ablation.

  • C. It blocks TSH receptors

    TSH-receptor antibodies stimulate Graves disease; thionamides do not block the receptor.

  • D. It inhibits peripheral conversion of T4 to T3 (correct)

    Correct. Peripheral deiodinase inhibition is PTU's additional action.

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.

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Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is D, It inhibits peripheral conversion of T4 to T3. Both thionamides inhibit thyroid peroxidase, but propylthiouracil also inhibits 5'-deiodinase, reducing T4-to-T3 conversion.

Why is "It replaces thyroid hormone" not the answer?

Levothyroxine replaces thyroid hormone.

Why is "It destroys thyroid follicles with beta radiation" not the answer?

Radioiodine causes beta-radiation-mediated ablation.

Why is "It blocks TSH receptors" not the answer?

TSH-receptor antibodies stimulate Graves disease; thionamides do not block the receptor.

What concept does this question test?

It tests Thyroid drugs: propylthiouracil in Pharmacology. This is useful in thyroid storm, though hepatotoxicity limits routine use.

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 Thyroid drugs: propylthiouracil?

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.