PEM board review: malathion organophosphate poisoning requires atropine plus pralidoxime, with airway/oxygenation prioritized.
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In pediatric organophosphate poisoning, atropine treats muscarinic symptoms, but pralidoxime is added to reverse acetylcholinesterase inhibition (especially when respiratory compromise/weakness is present).
A 2 yo boy is found vomiting after ingestion of unknown amount of malathion in the garage. Upon arrival, he is actively vomiting. His vitals are T 37.3°C HR 80 RR 30 BP 96/45 SpO2 90% on room air. On exam he is wheezing with increased secretions, and he appears lethargic.
In addition to atropine what additional medication is the appropriate treatment?
Answer Options:
This item is keyed correctly. For clinically significant organophosphate toxicity (bronchorrhea/bronchospasm, hypoxemia, lethargy), major consensus guidance supports atropine plus an oxime (pralidoxime) alongside aggressive supportive care (airway, oxygenation, suctioning, decontamination as appropriate). AAP pediatric poisoning resources and CDC/ATSDR clinical guidance consistently describe atropine for muscarinic features (bronchorrhea, bronchospasm, bradycardia) and pralidoxime to regenerate acetylcholinesterase and mitigate nicotinic effects (weakness, respiratory failure), with greatest benefit when given early.
Why it matters for boards: exam writers often build these stems around pulmonary secretions/hypoxemia to force recognition that atropine alone is not the complete antidotal strategy for organophosphates.
| Option | What It Tests / Implies | Why It’s Wrong Here |
| Naloxone | Opioid toxidrome (miosis, respiratory depression) | This child has secretions, wheeze/bronchorrhea, cholinergic findings; naloxone won’t reverse cholinesterase inhibition. |
| Physostigmine | Antimuscarinic (anticholinergic) delirium treatment | Physostigmine inhibits acetylcholinesterase, which would worsen organophosphate poisoning. |
| Pralidoxime | Oxime therapy to regenerate AChE | Correct: paired with atropine in significant organophosphate toxicity per consensus guidance (AAP/CDC/ATSDR). |
| Succimer | Chelation for lead (and some heavy metals) | No heavy metal scenario; succimer does not treat cholinergic crisis. |
Organophosphate poisoning with bronchorrhea/bronchospasm or weakness = atropine for muscarinic symptoms + pralidoxime (2-PAM) early to restore acetylcholinesterase function.
The stem deliberately includes “unknown amount” and prominent vomiting to invite generic overdose thinking, but the discriminators are wheezing, increased secretions, hypoxemia, and lethargy—a board-classic cholinergic crisis pattern where atropine alone is incomplete and pralidoxime is the specific adjunct.
A 4-year-old with pesticide exposure has miosis, copious secretions, wheezing, and bradycardia. What is the best antidotal regimen?
A 16-year-old is agitated, hallucinating, febrile, tachycardic, with dry skin and urinary retention after ingesting diphenhydramine. Best antidote?
A farm worker exposed to an organophosphate has fasciculations and progressive weakness requiring ventilatory support despite high-dose atropine controlling secretions. Next best medication?
Which best describes pralidoxime’s primary role in organophosphate poisoning?
A 2-year-old with suspected organophosphate ingestion is hypoxemic with bronchorrhea and wheezing. First priority in management?
How would your management differ if this ingestion were a carbamate insecticide rather than an organophosphate—particularly regarding the expected benefit and urgency of pralidoxime?
Q1: Why isn’t atropine alone sufficient in significant organophosphate poisoning?
A: The ABP/PEM-style expectation is that atropine treats muscarinic findings (bronchorrhea/bronchospasm/bradycardia), while pralidoxime is added to address nicotinic weakness and help restore AChE activity (AAP/CDC/ATSDR consensus).
Q2: What clinical clue pushes you toward adding pralidoxime?
A: Respiratory compromise (hypoxemia, bronchorrhea) and/or neuromuscular findings (fasciculations, weakness) signal clinically significant poisoning where oxime therapy is exam-reliable.
Q3: Why is physostigmine dangerous here?
A: Physostigmine inhibits acetylcholinesterase and can worsen cholinergic toxicity in organophosphate exposure—this contrast is a common board trap.
Q4: What’s the most important first step in a child with organophosphate exposure and low SpO2?
A: Airway and breathing (oxygen, suctioning, ventilation as needed); antidotes follow stabilization—frequently tested in pediatric emergency scenarios.
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