Toxicology & Poisoning — Comprehensive Study Notes Summary & Study Notes

📄 Summary (Harrison's Toxicology QuickNotes)

Epidemiology & Key Facts

Acute poisonings are usually acute, accidental, single-agent events occurring at home, often in children < 6 years. In the U.S., >5 million exposures are reported yearly; acetaminophen and carbon monoxide ($CO$) are leading causes of fatal poisoning. Global problems include high morbidity and mortality from snakebites in developing countries.

🚨 Emergency Stabilization

Primary goal: resuscitation and stabilization during the "toxic phase." Prioritize Airway, Breathing, Circulation, Disability, and Exposure (ABCDE).

• Airway: Endotracheal intubation for CNS depression or seizures to prevent aspiration.
• Breathing: Monitor for respiratory depression; use continuous pulse oximetry or arterial blood gases. Mechanical ventilation as needed.
• Circulation: IV access, cardiac monitoring, maintain perfusion. Use vasopressors (e.g., norepinephrine) if hypotension persists despite fluids.
• Disability (Neuro): Give IV glucose (unless known normal glucose), naloxone, and vitamin $B_6$ (pyridoxine) as indicated. Treat seizures promptly with benzodiazepines (first-line).
• Exposure: Measure core temperature; treat hyper-/hypothermia. Recognize hyperthermia as a poor prognostic sign in stimulant toxicity or withdrawal.

🩺 Evaluation & Diagnosis

History: time, route, amount, name of agent(s), onset of symptoms, and context. Obtain collateral history and inspect belongings. Use pill imprint codes or SDS for occupational exposures.

Physical exam & toxidrome recognition: Focus on vitals, pupils, skin, bowel sounds, neuromuscular findings. Pattern recognition of toxidromes guides early therapy (e.g., sympathomimetic vs anticholinergic vs cholinergic vs opioid syndromes).

Common toxidrome features:

• Sympathomimetic: tachycardia, hypertension, mydriasis, diaphoresis (e.g., cocaine, amphetamines).
• Anticholinergic: hot, dry, flushed, urinary retention, marked mydriasis (e.g., antihistamines, TCAs).
• Cholinergic (organophosphates): miosis, SLUDGE (salivation, lacrimation, urination, defecation, GI upset, emesis), nicotinic weakness/fasciculations.
• Opioid/GABAergic: CNS and respiratory depression, miosis.
• Membrane-active agents (TCAs/antiarrhythmics): coma, seizures, hypotension, QRS prolongation.
• AGMA inducers: methanol, ethylene glycol, salicylates — watch for metabolic acidosis and anion gap.

🔬 Laboratory & Diagnostic Tools

• Baseline labs: electrolytes, glucose, renal/hepatic panels, lactate, arterial blood gas.
• Anion gap metabolic acidosis (AGMA): suggests methanol, ethylene glycol, salicylates, or advanced shock/seizures.
• Osmolal gap (>10 mmol/L): suggests low-molecular-weight toxins (e.g., alcohols, glycols).
• ECG: look for bradycardia/AV block (beta-blockers, CCBs, digoxin), QRS widening (TCAs, antiarrhythmics), QT prolongation (antipsychotics, some antiarrhythmics).
• Toxicology testing: qualitative urine screens for severe/unexplained toxicity (limited by false results and inability to detect many novel agents). Quantitative serum levels guide management for specific toxins (e.g., acetaminophen, ethanol, ethylene glycol, methanol, salicylate, digoxin, lithium).

🛡️ Management Principles

Goals: support vitals, prevent further absorption, enhance elimination, give antidotes when indicated, and prevent re-exposure.

A. Supportive care: maintain physiology, prevent complications (aspiration, rhabdomyolysis, renal failure). ICU for severe poisonings or need for enhanced elimination.

B. Decontamination:

• Activated charcoal: 1 g/kg orally or via NG tube; most effective within 1 hour. Not effective for certain charged compounds (iron, lithium), strong acids/alkalis, or hydrocarbons when aspiration risk is high.
• Gastric lavage: rarely used; reserved for life-threatening ingestions not manageable otherwise. Contraindicated for corrosives and petroleum distillates.
• Whole-bowel irrigation (PEG): used for drug packets, sustained-release formulations, and substances poorly adsorbed by charcoal.
• Skin/eye decontamination: copious water/saline irrigation.

C. Enhanced elimination:

• Multiple-dose activated charcoal (MDAC): 0.5–1 g/kg every 2–4 hours for drugs with enterohepatic/enteric recycling (theophylline, phenobarbital, carbamazepine, dapsone, quinine).
• Urinary alkalinization: IV sodium bicarbonate to achieve urine pH ≥7.5 and high urine output to enhance excretion of salicylates and other weak acids.
• Extracorporeal removal (hemodialysis): indicated for small Vd (<1 L/kg), low protein binding, water-soluble toxins or severe toxicity (e.g., lithium, methanol, ethylene glycol, salicylates, theophylline, valproate, carbamazepine).

D. Antidotes: know key antidotes and their indications.

• Acetaminophen: N-acetylcysteine.
• Opioids: naloxone.
• Benzodiazepines: flumazenil (diagnostic use; use cautiously).
• Organophosphates (cholinergic): atropine for muscarinic signs; pralidoxime (2-PAM) for nicotinic symptoms and to reactivate cholinesterase.
• Cyanide: hydroxocobalamin or sodium nitrite + sodium thiosulfate.
• Methanol / Ethylene glycol: fomepizole (preferred) or ethanol.
• Digoxin toxicity: digoxin-specific antibody fragments.
• Beta-blocker / CCB overdose: glucagon, high-dose insulin with dextrose, calcium.
• Methemoglobinemia: methylene blue.
• Isoniazid (seizures): pyridoxine (vitamin $B_6$).
• Membrane-active agent (QRS widening): sodium bicarbonate therapy.

E. Prevention of re-exposure: patient education, safe medication storage, supervised dosing for adults at risk, and psychiatric referral for intentional overdoses.

✅ Practical Tips & Red Flags

• Consider toxidrome-driven empiric therapy when history is lacking and the patient is unstable.
• Use activated charcoal early when appropriate, but avoid when aspiration risk or corrosive ingestion exists.
• Recognize delayed toxicity ("toxic time-bombs"): sustained-release formulations and agents needing metabolic activation (e.g., methanol, acetaminophen) require prolonged monitoring and follow-up testing.
• Escalate to hemodialysis when indicated by toxin properties or severe clinical/lab abnormalities.

🧾 Quick-reference Antidotes (condensed)

A concise list: N-acetylcysteine (acetaminophen); naloxone (opioids); atropine + pralidoxime (organophosphates); fomepizole/ethanol (methanol, ethylene glycol); hydroxocobalamin (cyanide); digoxin-specific Fab (digoxin); sodium bicarbonate (TCA/membrane-active QRS widening); methylene blue (methemoglobinemia); pyridoxine (isoniazid).

📌 Takeaway

Rapid recognition, airway/ventilatory support, targeted decontamination, timely antidote administration, and appropriate use of enhanced elimination (including dialysis) are the pillars of acute poisoning management. Always integrate toxidrome recognition with laboratory data and clinical trajectory to guide urgent interventions.

📝 User Request (Context)

The user requested comprehensive study notes to support creation of multiple-choice questions with a distribution of 40% simple recall and 60% case-based items. These notes emphasize high-yield facts, toxidrome recognition, initial management steps, diagnostic clues (anion/osmolal gaps, ECG patterns), decontamination strategies, enhanced elimination criteria, and a concise antidote list to facilitate both recall and clinical reasoning questions.