Poisoning — Causes, Symptoms, Emergency Treatment & Prevention Guide — Symptoms, Causes & Treatment | MyMedicPlus

Poisoning is exposure to a substance (chemical, drug, natural toxin, or environmental hazard) in quantities sufficient to cause physiological harm. It encompasses intentional overdose (self-poisoning — the most common form in high-income countries), accidental ingestion (most common in children under 5), occupational exposure, and environmental contamination. The WHO estimates approximately 100,000 poisoning deaths occur annually worldwide. In high-income countries, medications account for the majority of poisoning cases, with paracetamol (acetaminophen) as the most common single cause. Carbon monoxide poisoning from incomplete combustion is the most common cause of fatal non-intentional poisoning in many countries. Rapid identification of the substance, dose, timing, and route of exposure is essential for directing specific treatment, and Poison Control Centres provide 24-hour specialist advice. The golden principle in poisoning management is early identification of the substance, dose, and time of ingestion, as specific antidotes — naloxone for opioids, N-acetylcysteine for paracetamol, digoxin-specific antibody fragments for digoxin — are highly effective only when administered within defined time windows.

Pharmaceutical overdoses: paracetamol (acetaminophen — most common; hepatotoxic at doses above 150 mg/kg or 7.5 g in adults); opioids (morphine, codeine, heroin, tramadol, fentanyl — CNS/respiratory depression); benzodiazepines (diazepam, lorazepam — sedation, respiratory depression); tricyclic antidepressants (amitriptyline — arrhythmias, seizures, anticholinergic effects); SSRIs (serotonin syndrome); antipsychotics; anticonvulsants. Household chemicals: caustic substances (bleach, drain cleaner — corrosive injuries to GI tract); organophosphate pesticides (acetylcholinesterase inhibition — bradycardia, bronchospasm, excessive secretions); alcohol (ethanol toxicity). Environmental toxins: carbon monoxide (CO — from faulty boilers, generators, fires in enclosed spaces — the 'silent killer'; binds haemoglobin with 250x affinity of oxygen); cyanide (industrial fires); heavy metals (lead, mercury, arsenic). Biological toxins: mushroom poisoning (Amanita phalloides — lethal hepatotoxicity); snake venom; botulinum toxin. Risk factors for accidental poisoning: children under 5, elderly with polypharmacy, those with mental health conditions, and occupational exposures.

Symptoms depend on the poison. Key toxidromes: Opioid syndrome: miosis (pinpoint pupils), reduced consciousness, respiratory depression, bradycardia — naloxone reverses. Anticholinergic syndrome (tricyclics, antihistamines, atropine): mydriasis, tachycardia, urinary retention, dry skin and mouth, confusion, delirium, seizures ('dry as a bone, blind as a bat, red as a beet, hot as a hare, mad as a hatter'). Cholinergic syndrome (organophosphates): SLUDGE — Salivation, Lacrimation, Urination, Defaecation, GI upset, Emesis; plus bradycardia, bronchospasm, miosis, seizures. Serotonin syndrome: agitation, tremor, myoclonus, hyperthermia, tachycardia, hyperreflexia (triad: cognitive changes + autonomic instability + neuromuscular abnormalities). Paracetamol overdose: often asymptomatic in first 24 hours; nausea, right upper quadrant pain; acute liver failure developing at 48-72 hours (jaundice, encephalopathy, coagulopathy). Carbon monoxide poisoning: headache, dizziness, nausea, confusion, 'cherry red' skin (unreliable), seizures, coma, cardiac arrest.

Clinical assessment: a thorough history (what was taken, how much, when, route — witnessed or inferred), physical examination for toxidromes, and mental state assessment. Blood tests: paracetamol level (mandatory in all overdoses presenting to ED — do not rely on history as patients underestimate dose; plot on Rumack-Matthew nomogram at 4 hours post-ingestion to determine N-acetylcysteine need); salicylate level; ethanol; electrolytes; glucose; ABG (metabolic acidosis in salicylate, methanol, ethylene glycol, metformin poisoning); LFTs and INR (paracetamol hepatotoxicity); renal function; FBC; creatine kinase (rhabdomyolysis); troponin. ECG: QTc prolongation (antipsychotics, antidepressants, antihistamines, methadone — risk of torsades de pointes); QRS widening (TCAs — treated with IV sodium bicarbonate); bradyarrhythmias (calcium channel blockers, digoxin). Blood carboxyhaemoglobin (COHb) by co-oximetry for carbon monoxide poisoning — standard pulse oximetry is falsely normal. Urine toxicology (qualitative screen): detects opioids, benzodiazepines, cocaine, amphetamines, cannabis — useful for confirmation, not acute treatment decisions.

Resuscitation first: ABCDE approach — airway, breathing, circulation. Antidotes for specific poisons: N-acetylcysteine (NAC — IV infusion): antidote for paracetamol overdose; highly effective if given within 8-10 hours of ingestion; prevents glutathione depletion and hepatic necrosis; given based on paracetamol level and nomogram. Naloxone (0.4-2 mg IV/IM/intranasal): opioid antagonist — reverses CNS and respiratory depression; short-acting (duration 45-90 minutes) requiring repeated dosing or infusion if long-acting opioids. Flumazenil: benzodiazepine antagonist — rarely used clinically due to risk of precipitating seizures in mixed overdoses or chronic benzodiazepine users. Atropine (IV) and pralidoxime: organophosphate poisoning. Antivenom: snake envenomation. Digoxin-specific antibody fragments (Digibind/DigiFab): digoxin toxicity. High-flow 100% oxygen: carbon monoxide poisoning (reduces COHb half-life from 4-5 hours in room air to 60-90 minutes); hyperbaric oxygen for severe CO poisoning. Activated charcoal (50 g oral/NG tube): adsorbs many drugs/chemicals; most effective within 1 hour of ingestion; contraindicated for caustic agents, hydrocarbons, and if airway is unprotected. Whole bowel irrigation (PEG electrolyte solution): for iron, lithium, modified-release preparations. Haemodialysis for salicylates, lithium, methanol, ethylene glycol, and valproate toxicity.

Poisoning can cause severe, often irreversible complications affecting multiple organ systems depending on the substance. Acute liver failure is the most serious complication of paracetamol overdose — developing at 48-72 hours when hepatic glutathione reserves are depleted; severe cases meeting King's College Criteria (INR above 6.5, creatinine above 300 μmol/L, pH below 7.3) carry 80% mortality without emergency liver transplantation. Acute kidney injury occurs from direct nephrotoxins (paracetamol, NSAIDs, ethylene glycol, heavy metals) and from shock and rhabdomyolysis — may require dialysis. Respiratory failure from CNS depression (opioids, sedatives, alcohol) causes hypoxic brain injury, aspiration pneumonia, and ARDS. Cardiac arrhythmias from QTc prolongation (antipsychotics, methadone, tricyclics) cause torsades de pointes and ventricular fibrillation — potentially fatal. Tricyclic antidepressant overdose causes QRS widening and malignant ventricular arrhythmias. Permanent brain damage results from cerebral hypoxia (CO poisoning, opioid-induced respiratory arrest) or severe hypoglycaemia (insulin overdose). Caustic ingestion of acids or alkalis causes oesophageal and gastric chemical burns — leading to oesophageal stricture requiring long-term endoscopic dilatation. Serotonin syndrome progressing to hyperthermia, rhabdomyolysis, renal failure, and disseminated intravascular coagulation (DIC) is life-threatening without prompt recognition and treatment.

Store all medicines and household chemicals in child-resistant containers, out of reach and out of sight of children — secure in a locked cabinet. Never transfer medicines to food or drink containers. Dispose of unused or expired medications safely (pharmacy take-back programmes — do not flush down toilet). Install carbon monoxide detectors in all rooms with gas appliances, boilers, or fireplaces. Service boilers, gas appliances, and flues annually by Gas Safe registered engineers. Never run generators, barbecues, or camping stoves indoors. Recognise symptoms of CO poisoning (headache + nausea in multiple household members simultaneously = assume CO until proven otherwise). For intentional overdoses: mental health support, crisis services, safe medication prescribing (limit quantities dispensed at one time for at-risk patients), Medicines Use Review for elderly patients with complex polypharmacy.

Call emergency services (999/112/911) immediately for: any suspected poisoning with altered consciousness, breathing difficulty, seizures, or collapse. Do NOT make the person vomit unless specifically instructed by Poison Control — inducing vomiting can be harmful for caustic or hydrocarbon ingestion. For all intentional overdoses, go to the emergency department even if the person appears well — paracetamol overdose can be asymptomatic for 24 hours while severe liver damage develops. Contact Poison Control 24 hours (UK: 0344 892 0111; USA: 1-800-222-1222) for guidance on all suspected poisonings before symptoms develop. Bring the original container, packaging, or medication to hospital. Carbon monoxide: evacuate immediately, call 999, do not re-enter building until declared safe.