What is the antidote for PCM (Paracetamol) poisoning?

Appeared in: Punjab CHO - 2021

Explanation

Acetylcysteine (N-acetylcysteine or NAC) is the specific antidote for paracetamol (acetaminophen) poisoning.
Paracetamol overdose leads to the production of a toxic metabolite, N-acetyl-p-benzoquinone imine (NAPQI).
Normally, NAPQI is detoxified by glutathione in the liver. In an overdose, glutathione stores are depleted, allowing NAPQI to cause severe liver damage (hepatotoxicity).
Acetylcysteine works by acting as a precursor to glutathione, replenishing the liver's stores and enabling the detoxification of NAPQI, thereby preventing liver injury.

Option A: This is the antidote for magnesium sulfate toxicity, not paracetamol poisoning.
Option B: This is the antidote for benzodiazepine overdose.
Option D: This is the antidote for heparin overdose.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Pharmacology: Antidotes for Common Poisonings as background academic context rather than a clinical decision trigger.
Timely administration of acetylcysteine is critical for patient outcomes. It is most effective when given within 8-10 hours of paracetamol ingestion.
Nurses must monitor for anaphylactoid (non-allergic) reactions during IV infusion of acetylcysteine, which can include rash, flushing, and bronchospasm. The infusion may need to be temporarily stopped and antihistamines administered.
Treatment decisions are guided by the Rumack-Matthew nomogram, which plots serum paracetamol levels against the time since ingestion to assess the risk of hepatotoxicity and the need for NAC.

How to Approach the Question

This is a factual recall question from pharmacology.
First, identify the key drug mentioned: Paracetamol (PCM).
The question asks for the specific 'antidote'.
Systematically review the options, recalling the specific antidotes for common drug toxicities.
Eliminate options known to be antidotes for other substances: Flumazenil (benzodiazepines), Protamine Sulphate (heparin), and Calcium Gluconate (magnesium sulfate).
Select Acetylcysteine as the known, specific antidote for paracetamol poisoning.

Concept Tested & Keywords

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E6 Medicine Davidson Principles Practice 24e p. 158-160

KD Tripathi - Essentials of Medical Pharmacology (6th Edition) p. 127-129

Practise the full Punjab CHO - 2021

Attempt every question from this paper in a timed mock, then review the full solution for each one.