Mood stabilisers: lithium toxicity: 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 · Mood stabilisers: lithium toxicity

Sample item

A 40-year-old woman on long-term lithium has polyuria with 5 litres of dilute urine daily that does not respond to desmopressin. Which drug can reduce the polyuria?

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

The answer and the reasoning

A. Amiloride

Lithium causes nephrogenic diabetes insipidus by entering collecting duct cells through the epithelial sodium channel and impairing the response to ADH. Amiloride blocks that channel, reducing lithium uptake and helping the polyuria. Sodium restriction raises lithium levels by increasing proximal reabsorption.

Option by option

  • A. Amiloride (correct)

    Amiloride blocks lithium entry into collecting duct cells and reduces polyuria.

  • B. Additional lithium

    More lithium would increase the concentrating defect.

  • C. Dietary sodium restriction

    Sodium restriction raises lithium reabsorption and risks toxicity.

  • D. Demeclocycline

    Demeclocycline itself causes nephrogenic diabetes insipidus and would worsen it.

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 A, Amiloride. Lithium causes nephrogenic diabetes insipidus by entering collecting duct cells through the epithelial sodium channel and impairing the response to ADH.

Why is "Additional lithium" not the answer?

More lithium would increase the concentrating defect.

Why is "Dietary sodium restriction" not the answer?

Sodium restriction raises lithium reabsorption and risks toxicity.

Why is "Demeclocycline" not the answer?

Demeclocycline itself causes nephrogenic diabetes insipidus and would worsen it.

What concept does this question test?

It tests Mood stabilisers: lithium toxicity in Pharmacology. Amiloride blocks that channel, reducing lithium uptake and helping the polyuria. Sodium restriction raises lithium levels by increasing proximal reabsorption.

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 Mood stabilisers: lithium toxicity?

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.