Toxicology: activated charcoal: 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: activated charcoal

Sample item

A patient presents one hour after an overdose of a drug. For which drug is activated charcoal least useful because it adsorbs the drug poorly?

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

The answer and the reasoning

B. Lithium

Activated charcoal adsorbs most drugs, but it binds poorly to small ionic or polar substances such as lithium, iron, alcohols, acids, alkalis and heavy metals. Paracetamol, theophylline and phenobarbitone are well adsorbed, and multiple-dose charcoal also enhances elimination of theophylline and phenobarbitone. Lithium toxicity is managed with fluids and haemodialysis if severe.

Option by option

  • A. Paracetamol

    Paracetamol is readily adsorbed by charcoal soon after ingestion.

  • B. Lithium (correct)

    Correct. Lithium is a small ion that charcoal does not bind well.

  • C. Theophylline

    Theophylline is well adsorbed and multiple doses enhance its removal.

  • D. Phenobarbitone

    Phenobarbitone is well adsorbed and multiple doses increase its elimination.

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 B, Lithium. Activated charcoal adsorbs most drugs, but it binds poorly to small ionic or polar substances such as lithium, iron, alcohols, acids, alkalis and heavy metals.

Why is "Paracetamol" not the answer?

Paracetamol is readily adsorbed by charcoal soon after ingestion.

Why is "Theophylline" not the answer?

Theophylline is well adsorbed and multiple doses enhance its removal.

Why is "Phenobarbitone" not the answer?

Phenobarbitone is well adsorbed and multiple doses increase its elimination.

What concept does this question test?

It tests Toxicology: activated charcoal in Forensic Medicine. Paracetamol, theophylline and phenobarbitone are well adsorbed, and multiple-dose charcoal also enhances elimination of theophylline and phenobarbitone. Lithium toxicity is managed with fluids and haemodialysis if severe.

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 Toxicology: activated charcoal?

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.