Toxicology: paracetamol overdose timing: 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 · Toxicology: paracetamol overdose timing

Sample item

A man presents 10 hours after a single acute ingestion of about 25 g of paracetamol. A level is sent, and the result will take four hours. What is the most appropriate action?

AGive activated charcoal onlyBGive intravenous vitamin KCWait for the level before deciding on treatmentDStart N-acetylcysteine at once without waiting for the level

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

The answer and the reasoning

D. Start N-acetylcysteine at once without waiting for the level

The protective effect of N-acetylcysteine is greatest within 8 hours of ingestion and falls afterwards, so in a late presenter with a significant history treatment is started immediately and can be stopped if the level proves non-toxic. The nomogram is used from 4 hours after ingestion. Charcoal gives little benefit at 10 hours.

Option by option

A. Give activated charcoal only
Charcoal adsorbs only drug still in the gut and is of little use after 10 hours.
B. Give intravenous vitamin K
Vitamin K corrects warfarin effect and is not an antidote for paracetamol.
C. Wait for the level before deciding on treatment
Waiting four hours would postpone treatment past the period of best protection.
D. Start N-acetylcysteine at once without waiting for the level (correct)
Delay beyond 8 hours lowers the benefit, so treatment starts without waiting.

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.

Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is D, Start N-acetylcysteine at once without waiting for the level. The protective effect of N-acetylcysteine is greatest within 8 hours of ingestion and falls afterwards, so in a late presenter with a significant history treatment is started immediately and can be stopped if the level proves non-toxic.

Why is "Give activated charcoal only" not the answer?

Charcoal adsorbs only drug still in the gut and is of little use after 10 hours.

Why is "Give intravenous vitamin K" not the answer?

Vitamin K corrects warfarin effect and is not an antidote for paracetamol.

Why is "Wait for the level before deciding on treatment" not the answer?

Waiting four hours would postpone treatment past the period of best protection.

What concept does this question test?

It tests Toxicology: paracetamol overdose timing in Pharmacology. The nomogram is used from 4 hours after ingestion. Charcoal gives little benefit at 10 hours.

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: paracetamol overdose timing?

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.