Toxicology: dialysability of poisons: practice question

A Forensic Medicine 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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Forensic Medicine · Toxicology: dialysability of poisons

Sample item

Haemodialysis is helpful for several poisonings. Which of the following drugs is least likely to be removed effectively by it because of a large volume of distribution and high tissue binding?

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

The answer and the reasoning

A. Amitriptyline

Dialysis removes substances that are small, water soluble, not highly protein bound and have a small volume of distribution. Methanol, lithium and salicylate (at high levels) fit this and are dialysed, while tricyclic antidepressants are highly lipophilic and tissue bound, and cannot be cleared.

Option by option

  • A. Amitriptyline (correct)

    Correct. Amitriptyline is lipophilic and widely distributed, so dialysis removes little.

  • B. Lithium

    Lithium is a small ion with little protein binding and is dialysed well.

  • C. Salicylate

    Salicylate is dialysable, especially at high concentrations, and dialysis also corrects acidosis.

  • D. Methanol

    Methanol is small and water soluble, and is removed by dialysis.

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 Forensic Medicine question

What is the answer to this Forensic Medicine question?

The best answer is A, Amitriptyline. Dialysis removes substances that are small, water soluble, not highly protein bound and have a small volume of distribution.

Why is "Lithium" not the answer?

Lithium is a small ion with little protein binding and is dialysed well.

Why is "Salicylate" not the answer?

Salicylate is dialysable, especially at high concentrations, and dialysis also corrects acidosis.

Why is "Methanol" not the answer?

Methanol is small and water soluble, and is removed by dialysis.

What concept does this question test?

It tests Toxicology: dialysability of poisons in Forensic Medicine. Methanol, lithium and salicylate (at high levels) fit this and are dialysed, while tricyclic antidepressants are highly lipophilic and tissue bound, and cannot be cleared.

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 Toxicology: dialysability of poisons?

Learn postmortem changes with their timelines, and toxicology as poison, sign, test and antidote. Then use the flashcards and the other Forensic Medicine 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.