Overdose and poisoning
Treat the patient first: airway, breathing, sugar and ECG. Then find out what, how much and when, check paracetamol levels in everyone, and give the specific antidote if there is one.
A 19-year-old woman says she took "a whole strip" of paracetamol and some of her mother's sleeping tablets about 5 hours ago after an argument. She is drowsy but rousable. Pulse 92, BP 112/70, RR 14, SpO₂ 97%. She weighs 50 kg.
What do you need to know, and do you start acetylcysteine now?
- A to EProtect the airway, oxygen if needed, recovery position if drowsy.
- Blood sugar and temperatureLow sugar is common and easy to treat.
- 12-lead ECGQRS and QT width. Broad QRS suggests tricyclics.
- What, how much, when, and whyAsk the patient, family, ambulance staff. Bring the packets.
- BloodsParacetamol and salicylate levels in everyone, gas, sugar, creatinine, LFTs, INR.
- Specific antidoteAcetylcysteine, naloxone, bicarbonate, and others as indicated.
- Check a poisons referenceOr call a poison centre for anything unusual.
- Safety and mental healthWatch for further self-harm. Psychiatric assessment before discharge.
- Drowsy, GCS 8 or less, airway at risk
- Pinpoint pupils and slow breathing
- Broad QRS, arrhythmia or fits
- Low BP
- Agitated, hot and sweaty
- Pesticide or wheat pill ingestion
- Silent paracetamol overdose
- Mixed overdose
- Organophosphate or aluminium phosphide poisoning
- Low sugar
- Ongoing risk to self after discharge
| Paracetamol level | Take at 4 hours after ingestion or later. Earlier levels cannot be interpreted |
| Acetylcysteine | Start straight away if over 150 mg/kg, staggered, unknown time, or more than 8 hours ago. Doses in the treatment section |
| Opioid with slow breathing | Naloxone, titrated to breathing |
| Broad QRS above 100 ms | Sodium bicarbonate (tricyclics) |
| Flumazenil | Avoid. Senior only |
Check every dose against a current drug reference and your hospital protocol.
On this page
First steps
Treat the patient in front of you before identifying the poison. Most poisoned patients survive with good basic care: airway, breathing, circulation, sugar, temperature and fits.
- Pinpoint pupils
- Slow, shallow breathing
- Drowsy
- Naloxone
- Big pupils, hot dry skin
- Fast pulse, confusion
- Urinary retention
- Broad QRS with tricyclics
- Small pupils, drooling, sweating
- Bronchorrhoea, slow pulse
- Atropine
- Big pupils, sweaty, hot
- Fast pulse, high BP, agitation
- Benzodiazepines, cooling
Paracetamol
Paracetamol is in almost every home, and an overdose can look completely well for the first day while the liver is being damaged. Check a paracetamol level in every overdose, even when the patient denies taking it.
- Time of ingestionSingle dose at a known time, or staggered over hours?
- AmountTotal mg divided by weight in kg.
- Start acetylcysteine now ifOver 150 mg/kg, staggered, time unknown, more than 8 hours ago, or the patient is jaundiced or unwell.
- Single known time, 4–8 hours agoTake a level at 4 hours or later and plot on the treatment line. Treat if on or above the line.
- Bloods at the start and end of treatmentLFTs, INR, creatinine, gas.
- Before stoppingLFTs and INR normal (or improving) and paracetamol undetectable, per protocol.
- Liver failure signsRising INR, acidosis, low sugar, confusion: senior and liver unit.
Opioids
- Support breathing with a bag-valve-mask while the naloxone works.
- In opioid-dependent patients, a big dose causes sudden withdrawal, vomiting and agitation.
Benzodiazepines and sleeping tablets
- Supportive care: airway, breathing, observation. Most recover.
- Flumazenil is not routinely used. It can cause fits, especially in mixed overdoses with tricyclics and in regular benzodiazepine users. Senior decision only.
Tricyclic antidepressants (amitriptyline)
Drowsiness, fits, big pupils, fast pulse, low BP and broad QRS (above 100 ms) with arrhythmias.
- Monitor ECG continuously.
- Sodium bicarbonate for QRS above 100 ms, arrhythmia or low BP.
- Benzodiazepines for fits. Avoid flumazenil and other drugs that lower the fit threshold.
- ICU review early.
Common poisons in Pakistan
| Poison | Key point | Guide |
|---|---|---|
| Organophosphate pesticides | Atropine, doubling the dose | Organophosphate poisoning |
| Wheat pills (aluminium phosphide) | No antidote. ICU, support the heart | Wheat pill poisoning |
| Paracetamol | Often silent at first. Acetylcysteine | This guide |
| Benzodiazepines and sleeping tablets | Supportive care | This guide |
| Kerosene (hydrocarbons) | Aspiration pneumonia. Do not induce vomiting | Senior advice |
| Rat poison (warfarin-like) | Delayed bleeding. Check INR. Vitamin K | Senior advice |
| Hair dye (paraphenylenediamine) | Throat and tongue swelling, muscle breakdown, kidney failure. Airway early | Senior and ICU |
| Methanol (contaminated alcohol) | Vision problems, severe acidosis | Senior and poison centre |
Decontamination
- Activated charcoal (50 g) may help within 1 hour of a dangerous amount of a substance it binds, if the airway is safe. It does not bind iron, lithium, alcohols, acids, alkalis or hydrocarbons.
- Do not induce vomiting.
- Gastric lavage is rarely indicated: senior decision only.
After treatment: safety
- Every intentional overdose needs a psychiatric or mental health assessment before discharge.
- Ask directly about suicidal thoughts and plans. Asking does not increase the risk.
- Remove access to the means where possible (pesticides, tablets at home).
- Do not let the patient leave alone before assessment if there is ongoing risk.
- Treat the patient with respect. Many patients are ashamed or frightened.
Common mistakes
- Not checking a paracetamol level because the patient "only took sleeping pills".
- Taking a paracetamol level at 2 hours and using it to decide treatment.
- Waiting for the level before starting acetylcysteine in a staggered or late overdose.
- Giving a large naloxone dose to an opioid-dependent patient.
- Giving flumazenil.
- Discharging after an intentional overdose without mental health assessment.
Frequently asked questions
When should acetylcysteine be started in paracetamol overdose?
Immediately if more than 150 mg/kg was taken, the overdose was staggered, the time is unknown, it was more than 8 hours ago, or the patient is unwell or jaundiced. Otherwise, take a level at 4 hours or later and treat if it is on or above the treatment line.
What is the naloxone dose for opioid overdose?
0.4 mg IV, repeated every 2–3 minutes up to 2 mg, titrated to breathing. Use smaller doses in opioid-dependent patients.
How is tricyclic overdose treated?
Supportive care, continuous ECG monitoring, sodium bicarbonate for a QRS above 100 ms, arrhythmias or low BP, and benzodiazepines for fits.
Test yourself
Exam-style questions on this guide, from our two question banks. Choose an answer to see why each option is right or wrong.
1. A 50 kg woman took about 8 g of paracetamol 5 hours ago. What is the best management?
Answer: Start acetylcysteine now and send a paracetamol level. About 160 mg/kg is above the 150 mg/kg treatment threshold. Where a paracetamol level cannot be back before 8 hours after ingestion (common in many Pakistani hospitals), start acetylcysteine now and send the level at the same time.
- Activated charcoal only: Too late and inadequate.
- Wait for the 4-hour level: She is already beyond 4 hours and has taken above 150 mg/kg.
- Discharge if she feels well: Liver injury appears later.
- Give acetylcysteine only if ALT is raised: Don't wait for liver injury.
2. A drowsy patient has pinpoint pupils and a respiratory rate of 6. What is the first drug?
Answer: IV naloxone. Opioid toxicity: support breathing with a bag-valve-mask and titrate naloxone. Watch for re-sedation with long-acting opioids.
- Atropine: Not for opioid toxicity.
- Physostigmine: Not indicated.
- Activated charcoal: Airway risk.
- Flumazenil: Can cause fits; not first-line.
3. A patient with amitriptyline overdose has a QRS duration of 128 ms. What is the treatment?
Answer: IV sodium bicarbonate. Sodium bicarbonate is given for QRS widening, arrhythmias or acidosis in tricyclic overdose.
- IV amiodarone infusion: Not first-line.
- IV flumazenil: Causes fits in tricyclic overdose.
- Physostigmine: Dangerous.
- Observe on a cardiac monitor: QRS widening predicts arrhythmias and fits.
4. A 19-year-old took 40 paracetamol tablets (500 mg) 6 hours ago. She weighs 50 kg. The 4-hour level was not taken. What should be done?
Answer: Start acetylcysteine now. Paracetamol 20 g in 50 kg = 400 mg/kg — a potentially fatal dose (> 150 mg/kg). NAPQI accumulates when glutathione is depleted, causing centrilobular necrosis. Give acetylcysteine (replenishes glutathione) when the level is above the treatment line on the nomogram at ≥ 4 h, or immediately if > 8 hours post-ingestion, staggered overdose or uncertain timing with significant dose. Charcoal is useful within 1 hour. Check INR, creatinine, pH, lactate; King’s College criteria guide transplant referral.
- Wait for the 8-hour level: Waiting for the level delays treatment beyond 8 hours.
- Activated charcoal only: Charcoal is too late as the only treatment.
- Discharge if LFTs normal: LFTs are normal early, so they do not exclude toxicity.
5. A 3-year-old (14 kg) drank an unknown amount of paracetamol syrup 2 hours ago. Possible ingestion is 2 g. What is the next step?
Answer: Paracetamol level at 4 hours. Estimate the ingested dose: 2 g/14 kg ≈ 143 mg/kg — potentially toxic (> 150 mg/kg; some use 75 mg/kg for high-risk). Measure the paracetamol level at 4 hours post-ingestion and treat with acetylcysteine if above the nomogram line; start immediately if presenting > 8 h with significant ingestion. Activated charcoal within 1 hour. Prevent with child-resistant containers and safe storage.
- Discharge — syrups are safe: A toxic dose is possible (over 140 mg/kg).
- Induce vomiting: Inducing vomiting is not recommended.
- Start N-acetylcysteine only if jaundiced: Waiting for jaundice is far too late.
6. In carbon monoxide poisoning, which finding is expected?
Answer: Normal PaO₂, low O₂ content. CO binds haemoglobin about 240 times more strongly than oxygen, forming carboxyhaemoglobin. Dissolved oxygen (PO₂) is normal, but oxygen content falls, and the curve shifts left so remaining oxygen is released poorly. Standard pulse oximeters read carboxyhaemoglobin as oxyhaemoglobin, giving falsely normal readings. Treat with 100% oxygen (hyperbaric if severe).
- Low arterial PO₂: PO₂ is normal.
- Oximetry shows low SpO₂ accurately: Pulse oximetry is falsely normal.
- Curve shifts to the right: Shifts to the left.
- Haemoglobin concentration falls: Haemoglobin amount is unchanged.
7. A young woman took a large paracetamol overdose 6 hours ago, and her paracetamol level is above the treatment line. Which antidote should be given?
Answer: N-acetylcysteine. In overdose, excess paracetamol is converted by CYP450 to NAPQI, a toxic metabolite normally neutralised by glutathione. When glutathione runs out, NAPQI damages hepatocytes (centrilobular necrosis). N-acetylcysteine restores glutathione and is most effective within 8 hours, but helps at any time.
- Naloxone: Opioid antidote.
- Flumazenil: Benzodiazepine antidote.
- Atropine: Organophosphate antidote.
- Phytomenadione: Warfarin reversal; does not treat the cause.
References and dose sources
- TOXBASE (UK National Poisons Information Service)
- Royal College of Emergency Medicine (RCEM) guidance
- TOXBASE
- Resuscitation Council UK
- Acetylcysteine (NAC) dosing: Drugs.com: Acetylcysteine dosage (see also our acetylcysteine (nac) dose page)
- Naloxone dosing: Drugs.com: Naloxone dosage (see also our naloxone dose page)
- Sodium bicarbonate dosing: Drugs.com: Sodium bicarbonate dosage (see also our sodium bicarbonate dose page)
International guidance is linked where it reflects good practice. Where your hospital’s protocol differs, follow your hospital.