Posterior pituitary drugs: tolvaptan: 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 · Posterior pituitary drugs: tolvaptan

Sample item

A 66-year-old man with lung cancer has euvolaemic hyponatraemia from SIADH, sodium 118 mmol/L with mild symptoms, and tolvaptan is started in hospital. What is the most important risk to monitor for?

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

The answer and the reasoning

B. Overly rapid rise in serum sodium, risking osmotic demyelination

Tolvaptan is a V2 receptor antagonist that causes aquaresis, excretion of free water, and so corrects hyponatraemia in SIADH. If sodium rises too fast (above about 8 to 10 mmol/L in 24 hours), osmotic demyelination can follow, so it is started under close monitoring of sodium. Hepatotoxicity is another warning.

Option by option

  • A. Hyperkalaemia from distal tubular effect

    Tolvaptan does not act on distal potassium handling and is not a potassium-sparing agent.

  • B. Overly rapid rise in serum sodium, risking osmotic demyelination (correct)

    Correct. Rapid aquaresis can overcorrect sodium, causing osmotic demyelination.

  • C. Fluid retention and weight gain

    It promotes water loss rather than retention.

  • D. Hypoglycaemia from reduced gluconeogenesis

    It has no effect on gluconeogenesis or glucose.

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 B, Overly rapid rise in serum sodium, risking osmotic demyelination. Tolvaptan is a V2 receptor antagonist that causes aquaresis, excretion of free water, and so corrects hyponatraemia in SIADH.

Why is "Hyperkalaemia from distal tubular effect" not the answer?

Tolvaptan does not act on distal potassium handling and is not a potassium-sparing agent.

Why is "Fluid retention and weight gain" not the answer?

It promotes water loss rather than retention.

Why is "Hypoglycaemia from reduced gluconeogenesis" not the answer?

It has no effect on gluconeogenesis or glucose.

What concept does this question test?

It tests Posterior pituitary drugs: tolvaptan in Pharmacology. If sodium rises too fast (above about 8 to 10 mmol/L in 24 hours), osmotic demyelination can follow, so it is started under close monitoring of sodium. Hepatotoxicity is another warning.

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 Posterior pituitary drugs: tolvaptan?

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.