An infant ingests a pesticide. Which drug reverses the acetylcholinesterase block?

NORCET 1 - 2020

Pharmacology

Medium

Appeared in: NORCET 1 - 2020

Explanation

Pesticides, specifically organophosphates, cause toxicity by forming a stable bond with the acetylcholinesterase enzyme, inactivating it.
Pralidoxime (PAM) is an oxime compound specifically designed to act as a cholinesterase regenerator.
Its primary mechanism is to cleave the organophosphate from the enzyme, thereby reactivating acetylcholinesterase and reversing the toxic effects.
This action addresses the root cause of the poisoning by restoring the normal breakdown of acetylcholine at both nicotinic and muscarinic receptors.

Option B: Atropine does not reverse the acetylcholinesterase block. It only acts as a competitive antagonist at muscarinic receptors to block the effects of the accumulated acetylcholine.
Option C: Flumazenil is an antidote for benzodiazepine overdose, not pesticide poisoning.
Option D: Naloxone is an antidote for opioid overdose, not pesticide poisoning.

Visual 1: Diagram: A visual showing the synaptic cleft with acetylcholinesterase being blocked by an organophosphate, and then a second panel showing Pralidoxime binding to the complex and releasing the enzyme.
Visual 2: Flowchart: A simple flowchart illustrating the management of organophosphate poisoning, showing the initial administration of Atropine for symptoms followed by Pralidoxime for enzyme reactivation.

Clinical Relevance

Nursing practice connection: Use the key finding related to Antidotes for Organophosphate Poisoning to guide bedside assessment, documentation, and the next nursing action.
In organophosphate poisoning, time is critical. Pralidoxime is most effective if given before the enzyme-inhibitor complex 'ages' and becomes irreversible, which typically occurs within 24-48 hours.
Nurses must recognize the signs of cholinergic crisis (DUMBBELS: Diarrhea, Urination, Miosis, Bronchospasm/Bronchorrhea, Emesis, Lacrimation, Salivation) to initiate prompt treatment.
The combination of Atropine and Pralidoxime is the standard of care. Atropine dries secretions and stabilizes cardiovascular function, while Pralidoxime restores muscle strength and reverses paralysis, including respiratory muscle weakness.

How to Approach the Question

First, identify the class of toxin. 'Pesticide' often implies an organophosphate.
Next, understand the mechanism of toxicity mentioned: 'acetylcholinesterase block'. This means the enzyme that breaks down acetylcholine is inhibited.
The question asks for a drug that 'reverses' this block. This requires an antidote that directly acts on the inhibited enzyme.
Evaluate the options based on their mechanisms. Atropine blocks receptors (symptom control), while Pralidoxime reactivates the enzyme (reverses the block).
Eliminate Flumazenil and Naloxone as they are antidotes for different classes of drugs (benzodiazepines and opioids, respectively).
Select Pralidoxime as it is the only option that directly reverses the acetylcholinesterase block.

Concept Tested & Keywords

Concept Tested: Antidotes for Organophosphate Poisoning
Stem keywords: infant, pesticide, acetylcholinesterase block
Lead-in keywords: reverses
Clinical cues: The question asks for the drug that reverses the block, pointing to the specific mechanism of enzyme reactivation rather than symptom management.

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