Cardiovascular drugs: amiodarone and thyroid: 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 · Cardiovascular drugs: amiodarone and thyroid

Sample item

A 70-year-old man on amiodarone for atrial fibrillation for 8 months has weight gain, cold intolerance and constipation. TSH is 28 mIU/L and free T4 is low. What best explains the mechanism?

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

The answer and the reasoning

C. Iodine excess blocking hormone synthesis and release in a susceptible gland

Amiodarone contains about 37% iodine by weight, and it also inhibits peripheral conversion of T4 to T3. In patients who cannot escape the Wolff-Chaikoff effect, such as those with underlying autoimmune thyroiditis, hypothyroidism results. It can be treated with levothyroxine while the drug is continued if necessary.

Option by option

  • A. Competitive inhibition of iodide transport into the gland as with perchlorate

    Perchlorate and thiocyanate block the sodium-iodide symporter, which is not the main mechanism here.

  • B. Direct suppression of pituitary TSH release

    A raised TSH shows that the pituitary is responding, so suppression of TSH is not the cause.

  • C. Iodine excess blocking hormone synthesis and release in a susceptible gland (correct)

    Correct. The large iodine load shuts down thyroid hormone production in susceptible glands.

  • D. Autoantibody destruction of the gland triggered by the drug as a hapten

    Amiodarone is not a recognised hapten that induces gland-destroying autoantibodies.

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, Iodine excess blocking hormone synthesis and release in a susceptible gland. Amiodarone contains about 37% iodine by weight, and it also inhibits peripheral conversion of T4 to T3.

Why is "Competitive inhibition of iodide transport into the gland as with per…" not the answer?

Perchlorate and thiocyanate block the sodium-iodide symporter, which is not the main mechanism here.

Why is "Direct suppression of pituitary TSH release" not the answer?

A raised TSH shows that the pituitary is responding, so suppression of TSH is not the cause.

Why is "Autoantibody destruction of the gland triggered by the drug as a hapt…" not the answer?

Amiodarone is not a recognised hapten that induces gland-destroying autoantibodies.

What concept does this question test?

It tests Cardiovascular drugs: amiodarone and thyroid in Pharmacology. In patients who cannot escape the Wolff-Chaikoff effect, such as those with underlying autoimmune thyroiditis, hypothyroidism results. It can be treated with levothyroxine while the drug is continued if necessary.

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 Cardiovascular drugs: amiodarone and thyroid?

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.