Thyroid drugs: iodides: 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: iodides

Sample item

A patient with Graves disease is given Lugol's iodine for 10 days before thyroidectomy. What is the rationale?

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

The answer and the reasoning

C. It inhibits thyroid hormone release and reduces the gland's vascularity

Large doses of iodide inhibit proteolysis of thyroglobulin and release of hormone, and reduce thyroid blood flow, making the gland firmer and less vascular for surgery. It is given only for a short period because of the escape from the Wolff-Chaikoff effect. Perchlorate blocks iodide uptake, and propylthiouracil and propranolol inhibit peripheral conversion.

Option by option

  • A. It competitively blocks the sodium-iodide symporter as perchlorate does

    Competitive blockade of the symporter is the action of perchlorate and thiocyanate, not of iodide.

  • B. It destroys follicular cells like radioactive iodine

    Destruction of follicular cells is the effect of radioactive iodine.

  • C. It inhibits thyroid hormone release and reduces the gland's vascularity (correct)

    Correct. Iodide reduces release of stored hormone and makes the gland less vascular.

  • D. It blocks peripheral conversion of T4 to T3

    Inhibition of peripheral deiodination is the action of propylthiouracil, propranolol and glucocorticoids.

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 C, It inhibits thyroid hormone release and reduces the gland's vascularity. Large doses of iodide inhibit proteolysis of thyroglobulin and release of hormone, and reduce thyroid blood flow, making the gland firmer and less vascular for surgery.

Why is "It competitively blocks the sodium-iodide symporter as perchlorate do…" not the answer?

Competitive blockade of the symporter is the action of perchlorate and thiocyanate, not of iodide.

Why is "It destroys follicular cells like radioactive iodine" not the answer?

Destruction of follicular cells is the effect of radioactive iodine.

Why is "It blocks peripheral conversion of T4 to T3" not the answer?

Inhibition of peripheral deiodination is the action of propylthiouracil, propranolol and glucocorticoids.

What concept does this question test?

It tests Thyroid drugs: iodides in Pharmacology. It is given only for a short period because of the escape from the Wolff-Chaikoff effect. Perchlorate blocks iodide uptake, and propylthiouracil and propranolol inhibit peripheral conversion.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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: iodides?

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.