Key Facts

Poisoning is one of the most common reasons for emergency hospital admission in the UK. Most cases are due to intentional self-harm with medications. A systematic approach with ABCDE assessment, toxidrome recognition, and appropriate use of antidotes and decontamination is essential.

Epidemiology

Approximately 170,000 ED attendances for poisoning per year in England. Self-harm by poisoning accounts for approximately 100,000 hospital admissions annually. Paracetamol is the most commonly used agent in self-poisoning (~50% of cases). Approximately 200-300 deaths per year from poisoning in the UK (excluding illicit drugs).

Aetiology

• Intentional self-harm: Most common (~80%) — paracetamol, SSRIs, NSAIDs, opioids
• Recreational drug use: MDMA, cocaine, novel psychoactive substances, opioids
• Accidental: Children (<5 years), elderly (medication errors)
• Environmental: Carbon monoxide, organophosphates

Pathophysiology

Toxicological effects depend on the specific agent, dose, and route. Key mechanisms include:

• Receptor-mediated toxicity: Opioid receptor agonism, anticholinergic receptor blockade
• Enzyme inhibition: Organophosphate cholinesterase inhibition
• Metabolic toxicity: Paracetamol → NAPQI → hepatotoxicity
• Cardiotoxicity: Sodium channel blockade (TCAs), potassium channel effects (sotalol)

Toxidromes

• Anticholinergic: Tachycardia, dry mouth, dilated pupils, urinary retention, confusion, hyperthermia ('dry as a bone, blind as a bat, mad as a hatter')
• Cholinergic: SLUDGE — Salivation, Lacrimation, Urination, Diarrhoea, GI distress, Emesis; miosis, bradycardia, bronchorrhoea
• Sympathomimetic: Tachycardia, hypertension, hyperthermia, dilated pupils, agitation (cocaine, amphetamines)
• Opioid: Miosis, respiratory depression, reduced consciousness, hypotension, bradycardia
• Serotonin syndrome: Clonus, hyperreflexia, hyperthermia, agitation, mydriasis, tremor

Red Flags

• Altered consciousness (GCS <8) — secure airway, consider intubation
• Respiratory depression (RR <12, SpO2 <92%) — naloxone if opioid suspected; ventilatory support
• Cardiovascular compromise — wide QRS (TCAs), arrhythmias, hypotension
• Seizures — particularly with TCAs, tramadol, SSRIs, cocaine
• Hyperthermia >40°C — serotonin syndrome, MDMA, NMS
• Metabolic acidosis — paracetamol (late), methanol, ethylene glycol, salicylates

Bedside

• ABCDE assessment: Priority — secure airway if GCS ≤8
• Blood glucose: Hypoglycaemia (insulin, sulphonylureas) or hyperglycaemia
• ECG: QRS prolongation (TCAs), QTc prolongation (many drugs), arrhythmias
• Temperature: Hyperthermia (serotonin syndrome, NMS, MDMA, sympathomimetics)
• Pupil size: Miosis (opioids, organophosphates) or mydriasis (sympathomimetics, anticholinergics)

Bloods

• Paracetamol level: At 4 hours post-ingestion (or immediately if time unknown) — plot on treatment nomogram
• Salicylate level: If aspirin co-ingestion suspected
• ABG/VBG: pH, lactate, bicarbonate — metabolic acidosis significant
• U&Es, LFTs, coagulation: Organ function assessment
• FBC, glucose: Baseline
• Ethanol level: If alcohol co-ingestion
• Serum osmolality: If toxic alcohol suspected (osmolal gap)

Imaging

• CXR: If aspiration risk or pulmonary oedema
• CT head: If altered consciousness and cause unclear

Special Tests

• Urine drug screen: Limited clinical utility — does not change acute management in most cases
• Specific drug levels: Lithium, digoxin, iron, theophylline, carbamazepine, valproate
• TOXBASE: Consult for all poisoning cases

Non-pharmacological

• ABCDE approach: Secure airway, breathing, circulation first
• Decontamination: Activated charcoal 50g PO (1g/kg in children) if within 1 hour of ingestion of a potentially toxic substance; NOT if airway compromised
• Whole bowel irrigation: Polyethylene glycol — for sustained-release preparations, iron, lithium, body-packers
• Gastric lavage: Rarely indicated — only if life-threatening ingestion within 1 hour and charcoal not effective

Pharmacological

Specific antidotes:

• Paracetamol: N-acetylcysteine (NAC) — 150mg/kg in 200mL 5% glucose over 1h, then 50mg/kg in 500mL over 4h, then 100mg/kg in 1L over 16h
• Opioids: Naloxone 400mcg IV (titrate; may need repeated doses or infusion)
• Benzodiazepines: Flumazenil 200mcg IV (ONLY if pure benzodiazepine OD — risk of seizures with mixed OD)
• TCAs: Sodium bicarbonate 8.4% 50mL IV if QRS >120ms or arrhythmias
• Beta-blockers: Glucagon 2-10mg IV; high-dose insulin-euglycaemia therapy
• Calcium channel blockers: Calcium chloride 10mL 10% IV; high-dose insulin-euglycaemia therapy
• Organophosphates: Atropine 2mg IV doubling every 5 min + pralidoxime 30mg/kg IV
• Digoxin: Digibind (digoxin-specific Fab antibodies)
• Methanol/ethylene glycol: Fomepizole (20mg/kg IV) or ethanol infusion; haemodialysis

Surgical/Interventional

• Haemodialysis/haemofiltration: For salicylates, lithium, methanol, ethylene glycol, theophylline
• Intralipid 20%: For local anaesthetic toxicity, severe lipophilic drug cardiotoxicity

Referral Criteria

• NPIS (0344 892 0111): Complex or unusual poisoning
• ICU: GCS ≤8, haemodynamic instability, respiratory failure
• Psychiatric assessment: ALL intentional overdoses before discharge (NICE CG133)
• Safeguarding: Children with accidental ingestion — assess for neglect/NAI

• Overall mortality from poisoning: <1% with appropriate hospital management
• Paracetamol: Excellent if NAC given within 8 hours; mortality 0.4% with treatment vs ~5% without
• TCA overdose: Mortality ~2-5%; QRS >160ms associated with seizures and arrhythmias
• Opioid overdose: Excellent response to naloxone if given promptly; take-home naloxone programmes reduce community deaths
• Repeated self-harm: ~25% repeat within 1 year; ~3% die by suicide within 10 years

Key Antidotes Summary

Risk Assessment in Intentional Overdose