Endocrine drugs: demeclocycline in SIADH: 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 · Endocrine drugs: demeclocycline in SIADH

Sample item

A man with chronic SIADH and persistent hyponatraemia cannot tolerate fluid restriction. Which tetracycline derivative, which antagonises ADH action in the collecting duct, can be used?

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

The answer and the reasoning

D. Demeclocycline

Demeclocycline causes nephrogenic diabetes insipidus by reducing the response of the collecting duct to ADH, and so raises serum sodium in SIADH. Nephrotoxicity and photosensitivity limit use, and vaptans are alternatives.

Option by option

  • A. Minocycline

    Minocycline does not have this effect on the collecting duct.

  • B. Doxycycline

    Doxycycline does not have this effect on the collecting duct.

  • C. Tigecycline

    Tigecycline is a glycylcycline that does not antagonise ADH.

  • D. Demeclocycline (correct)

    Correct. Demeclocycline blunts the renal response to ADH.

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, Demeclocycline. Demeclocycline causes nephrogenic diabetes insipidus by reducing the response of the collecting duct to ADH, and so raises serum sodium in SIADH.

Why is "Minocycline" not the answer?

Minocycline does not have this effect on the collecting duct.

Why is "Doxycycline" not the answer?

Doxycycline does not have this effect on the collecting duct.

Why is "Tigecycline" not the answer?

Tigecycline is a glycylcycline that does not antagonise ADH.

What concept does this question test?

It tests Endocrine drugs: demeclocycline in SIADH in Pharmacology. Nephrotoxicity and photosensitivity limit use, and vaptans are alternatives.

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 Endocrine drugs: demeclocycline in SIADH?

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.