9.3 Poisoning & Toxicology

Poisoning & Toxicology

General Approach to the Poisoned Child

Pediatric poisoning vignettes on this exam almost always test sequencing (stabilize before decontaminating, decontaminate before giving an antidote) and recognizing when a "classic" intervention is actually contraindicated. The universal first steps are identical to any critically ill child: airway, breathing, and circulation, followed by a rapid glucose check (hypoglycemia mimics many toxidromes and is easily reversible), and a focused history covering what was taken, how much, when, and any co-ingestants.

Decontamination Principles

• Dermal/ocular exposure: remove contaminated clothing and irrigate skin/eyes copiously with water or saline; this is time-critical for corrosives and organophosphates and should not be delayed for transport.
• Gastric lavage: rarely used today; reserved for select life-threatening ingestions presenting very early, and contraindicated with an unprotected airway or after caustic/hydrocarbon ingestion because of aspiration and perforation risk.
• Whole bowel irrigation (polyethylene glycol solution): used for substances not bound by activated charcoal or that form concretions — classically iron, sustained-release or enteric-coated tablets, and ingested button batteries or drug packets awaiting passage.
• Syrup of ipecac: no longer recommended in any setting — removed from routine poisoning management because of lack of proven benefit and aspiration risk.

Activated Charcoal: Indications and Limits

Activated charcoal adsorbs many toxins onto its surface within the gut lumen, preventing systemic absorption.

• Dose: approximately 1 g/kg (typical range 1-2 g/kg in children), given orally or via nasogastric tube.
• Time window: most beneficial within 1 hour of ingestion; benefit drops sharply afterward, though it may still be considered for agents that slow gut motility or in massive ingestions.
• Requires a protected airway — contraindicated in a child with a depressed level of consciousness who cannot protect their airway unless the child is intubated first.
• Does NOT work well for: metals such as iron, lithium, alcohols/glycols, hydrocarbon solvents, and caustic acids/alkalis — a set of exceptions worth memorizing as a group, since charcoal simply does not bind small, highly water-soluble ions and corrosive agents well.

Exam trap: A vignette describing a toddler who swallowed iron tablets and asking for the next best step will list activated charcoal as a distractor. Iron is not adsorbed by charcoal; the correct next steps are an abdominal X-ray (iron tablets are radiopaque) and consideration of whole bowel irrigation or deferoxamine, not charcoal.

Key Pediatric Toxidromes

Specific Antidotes the Exam Expects You to Know

Iron

Iron toxicity progresses through overlapping stages: a gastrointestinal (GI) hemorrhagic phase (0-6 hours), a deceptive latent phase (6-24 hours), a shock/metabolic-acidosis/hepatotoxicity phase (12-48 hours), and a late gastric outlet or pyloric scarring phase (weeks later). Toxicity correlates with the elemental iron dose ingested:

• More than 20 mg/kg elemental iron: mild GI symptoms expected.
• More than 60 mg/kg elemental iron, or a serum iron level over 500 micrograms/dL, or clinical toxicity at any measurable level: chelation is indicated.
• Antidote: deferoxamine, an intravenous (IV) chelator typically infused starting around 15 mg/kg/hour and titrated to clinical response; classically produces pink-orange ("vin rose") colored urine as the iron-deferoxamine complex is excreted.

Acetaminophen (Paracetamol)

• The toxic acute-ingestion threshold is generally considered greater than 150 mg/kg.
• The Rumack-Matthew nomogram plots a single acute-ingestion serum acetaminophen level against time since ingestion (valid from 4 hours post-ingestion onward) to decide whether treatment is needed — it is not valid for staggered/chronic ingestions or presentations beyond 24 hours.
• Antidote: N-acetylcysteine (NAC), which replenishes hepatic glutathione stores. A typical oral regimen is a 140 mg/kg loading dose, then 70 mg/kg every 4 hours for 17 additional doses (a 72-hour course); IV regimens use a shorter two- or three-bag protocol.
• NAC is most effective when started within 8 hours of ingestion but still provides benefit later, including in established hepatotoxicity.

Organophosphates

• Atropine: an initial dose of approximately 0.02 mg/kg IV, repeated and doubled every 5 minutes until secretions dry and bronchospasm resolves; large cumulative doses may be needed in severe poisoning.
• Pralidoxime (2-PAM): reactivates acetylcholinesterase if given before the enzyme-organophosphate bond "ages" and becomes irreversible; most effective early in the course, given alongside atropine rather than as a substitute for it.
• Decontaminate the child (remove clothing, wash skin) before bringing them into an enclosed treatment space, to protect staff from secondary exposure.

Button Battery Ingestion — A True Pediatric Emergency

A swallowed button battery (especially the 20 mm, 3-volt lithium coin cell found in many toys and remote controls) lodged in the esophagus generates an external electrical current that hydrolyzes tissue fluid, creating localized caustic (alkaline) injury — severe esophageal burns can occur within 2 hours, with reports of fatal aortoesophageal fistula.

• Any child with a witnessed or suspected button battery ingestion needs an urgent X-ray to localize the battery — a battery lodged in the esophagus requires emergent endoscopic removal, ideally within 2 hours.
• A battery that has already passed into the stomach in an asymptomatic child can often be managed with outpatient follow-up imaging, since most batteries pass spontaneously once through the pylorus.
• If the ingestion is recent (less than 12 hours) and the child is 12 months of age or older, honey (10 mL every 10 minutes, up to 6 doses) or sucralfate may be given while arranging transfer and endoscopy — this is an adjunct that slows injury, not a substitute for emergent removal.
• Do not induce vomiting and do not give activated charcoal — neither removes the battery, and both delay definitive care.

Household-Hazard Prevention Counseling

The exam frequently tests prevention counseling as a stand-alone item embedded in a well-child visit or toxicology vignette:

• Store all medications, cleaning products, and chemicals in their original, child-resistant containers, locked and out of sight and reach — never in a repurposed food or drink container.
• Keep the regional or national poison control center number posted or saved in the phone of every caregiver.
• Store button batteries and battery-operated devices with the battery compartment secured, and dispose of used batteries immediately and safely.
• Never refer to medication as "candy" to encourage a child to take it.
• Toddlers (roughly ages 1-5) are the peak-incidence group for exploratory, single-substance ingestions, while intentional ingestions in adolescents are more often multi-substance and higher dose — a distinction the exam uses to test which historical clues predict severity.