What is the antidote for organophosphorus poisoning?

Appeared in: DSSSB 12 August 2024

Explanation

Organophosphorus (OP) compounds cause toxicity by irreversibly inhibiting the acetylcholinesterase enzyme, leading to an accumulation of acetylcholine (ACh) and a subsequent cholinergic crisis.
Atropine sulphate is a competitive antagonist at muscarinic ACh receptors.
It directly counteracts the life-threatening muscarinic effects of OP poisoning, such as severe bronchospasm, excessive respiratory secretions (bronchorrhea), and bradycardia.
Atropine is administered until clinical signs of 'atropinization' (dry skin and mouth, tachycardia, pupil dilation) are achieved, indicating a therapeutic effect.

Option B: Naloxone is an opioid receptor antagonist and has no effect on the cholinergic system.
Option C: N-acetylcysteine works by replenishing glutathione stores in the liver to detoxify a harmful metabolite of acetaminophen.
Option D: Physostigmine is a cholinesterase inhibitor. Administering it in organophosphorus poisoning would worsen the cholinergic crisis by further increasing acetylcholine levels.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Pharmacological management of organophosphorus poisoning as background academic context rather than a clinical decision trigger.
Prompt administration of atropine is a life-saving intervention in organophosphorus poisoning. Nurses must be able to recognize the cholinergic toxidrome (DUMBELS) and be prepared for immediate antidote administration.
Nursing monitoring includes assessing for signs of atropinization (dry mouth, tachycardia, dilated pupils, flushed skin) to titrate the dose effectively and avoid atropine toxicity.
Pralidoxime (PAM) is often given concurrently to reactivate the cholinesterase enzyme, addressing nicotinic symptoms like muscle weakness and paralysis, which atropine does not affect. This two-pronged approach is crucial for complete recovery.

How to Approach the Question

First, identify the core of the question: it asks for the specific antidote for 'organophosphorus poisoning'.
Recall the mechanism of organophosphorus compounds. They inhibit acetylcholinesterase, leading to an excess of acetylcholine (a cholinergic crisis).
Think about the pharmacological action needed to counteract this. The antidote must block the effects of excess acetylcholine.
Evaluate the options based on their known mechanisms:
Atropine is an anticholinergic agent, which directly opposes acetylcholine's effects.
Naloxone is an opioid antagonist.

Concept Tested & Keywords

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E6 Ghai Essential Pediatrics(pp 26-904 of 913) p. 755-757

E6 Pharmacology Nurses Shanbhag 3e p. 70-72

E6 Medicine Davidson Principles Practice 24e p. 166-168

Practise the full DSSSB 12 August 2024

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