Medical Toxicology: Toxidromes and Antidotes
Core concepts
The Toxicology domain tests recognition of toxidromes (anticholinergic, cholinergic, sympathomimetic, opioid, sedative-hypnotic, serotonin, and neuroleptic malignant syndrome), application of antidotes, and decisions about decontamination and enhanced elimination. Know the classic antidote pairs: naloxone for opioids, flumazenil for benzodiazepines (with caution), N-acetylcysteine for acetaminophen, sodium bicarbonate for salicylates and TCA cardiotoxicity, glucagon and high-dose insulin for beta-blocker toxicity, lipid emulsion for local anesthetics, hydroxocobalamin for cyanide, and fomepizole for methanol/ethylene glycol.
Traps to watch
- Giving flumazenil to a mixed overdose or seizure-prone patient - risk of precipitating seizures.
- Missing delayed toxicity. Acetaminophen and iron are notoriously delayed; a normal early level does not exclude toxicity.
- Forgetting that activated charcoal is contraindicated with altered mental status without airway protection, caustic ingestion, or hydrocarbon ingestion.
- Confusing cholinergic and anticholinergic findings. Cholinergic: SLUDGE/DUMBELS (bradycardia, salivation, lacrimation, diarrhea). Anticholinergic: dry, hot, red, blind, mad.
- Assuming dialysis is always indicated. It is for specific toxins (salicylates, methanol, ethylene glycol, lithium) with defined criteria.
Worked example
A patient presents with salicylate overdose: tinnitus, tachypnea, mixed respiratory alkalosis and metabolic acidosis. The trap answer is "give naloxone." The correct approach is serial salicylate levels, urine alkalinization with sodium bicarbonate, and hemodialysis for severe toxicity (altered mental status, pulmonary edema, renal failure, refractory acidosis). Rule of thumb: if the anion gap is elevated with an osmolar gap, think toxic alcohol and reach for fomepizole.