01Purpose and principlesWhat the treatment does and how it fits into care.
Poisoning is a dynamic clinical problem. The medicine or chemical may still be absorbing, active metabolites may emerge, and a patient who looks well initially may deteriorate later. A toxidrome is useful because several physiological findings can suggest a mechanism before the exact substance is known. It should remain a working hypothesis. A person with pinpoint pupils can also have a head injury, and an agitated tachycardic patient may have sepsis, withdrawal or more than one ingestion. The immediate objective is to protect oxygenation, ventilation, circulation and the brain while gathering enough exposure information to anticipate the next hazard.
Antidotes address particular mechanisms; they do not replace supportive care. Naloxone may restore breathing after opioid exposure, but recurrent depression can occur when the opioid lasts longer than the antagonist. Acetylcysteine reduces the risk of liver injury after relevant paracetamol exposure, but prescribing it safely still requires weight, concentration, infusion duration and follow-up blood tests. Other situations need specialist strategies, including treatment for sodium-channel blockade, toxic alcohols or cardiotoxic drug overdose. Use current TOXBASE or NPIS advice for the actual poison and circumstances. The clinically useful consultation supplies a precise timeline, formulation, estimated dose, observations, ECG and available investigations rather than only the name of a suspected tablet.
Key points
- Toxidromes are patterns that narrow a differential; mixed ingestion, delayed absorption and coexisting illness can prevent a textbook pattern from appearing.
- Opioid toxicity is suggested by reduced consciousness and inadequate breathing, often with small pupils. Support ventilation immediately and use naloxone for clinically important opioid-induced respiratory depression.
- The selected naloxone injection SmPC allows an adult overdose dose of 400–2,000 micrograms intravenously, repeated every 2–3 minutes according to response; titrate to effective breathing and use an appropriate lower-dose strategy when reversal could precipitate severe withdrawal.
- Agitation with sweating suggests sympathetic excess; dry skin, urinary retention and reduced bowel activity favour antimuscarinic effects. Clonus and hyperreflexia with autonomic disturbance raise serotonin toxicity.
- Obtain an ECG, glucose and relevant acid–base and electrolyte assessment early. A widening QRS or evolving arrhythmia requires urgent agent-specific treatment and specialist input.
- Paracetamol poisoning may initially cause few symptoms. For a potentially toxic overdose with uncertain timing or staggered ingestion, start IV acetylcysteine without delay using the approved overdose protocol while obtaining toxicology advice; do not wait for a nomogram decision or liver-injury symptoms.
- Acetylcysteine treatment and discharge require explicit clinical and laboratory decisions. Follow one complete approved regimen; do not mix the licensed three-infusion schedule with a different locally approved protocol.
02Indications, selection and cautionsWho may benefit, who needs urgent treatment and important alternatives.
Reduced respiratory rate or depth is the immediate concern in suspected opioid toxicity; pupil size supports but does not determine the diagnosis. Sedative co-ingestion may limit the response to naloxone. Check ventilation directly and assess airway protection, because supplemental oxygen can improve saturation while dangerous hypoventilation persists. A transient awakening is not proof that observation can end.
Sweating, tachycardia and agitation suggest sympathetic stimulation, while dryness, urinary retention and diminished bowel activity support antimuscarinic effects. Overlap is common and the exposure may be uncertain. Examine temperature and neuromuscular signs as well as pupils. A toxidrome helps prioritise questions and treatment; it is not a reliable identification label for an unknown street drug.
Clonus and hyperreflexia with agitation or autonomic instability raise serotonin toxicity, especially after a relevant combination or dose change. Excess salivation, bronchial secretions, diarrhoea and fasciculations suggest a cholinergic process. Consider responder contamination where an external chemical exposure is possible and follow appropriate safety procedures before close contact.
Early paracetamol toxicity may produce no distinctive physical pattern. Modified-release preparations and large or mixed ingestions can also prolong absorption. Obtain the formulation and timing rather than assuming that a reassuring first hour predicts the whole course. Ask about all accessible medicines, including combination analgesics that conceal an additional paracetamol dose.
03Assessment before treatmentTests and checks that guide safe selection.
Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.
- 01
Bedside glucose and repeated observationsFirst step - Why
- Identify reversible metabolic disturbance and track evolving physiology.
- Interpretation and limitations
- Record breathing rate and depth, consciousness, temperature, pulse and pressure, not only oxygen saturation. Repeat the observations after an intervention to establish whether it achieved the intended effect. Hypoglycaemia, hypoxia and hypercapnia can coexist with poisoning and need treatment even before the exposure is identified.
- 02
Electrocardiogram and continuous monitoring when indicated - Why
- Detect conduction disturbance and arrhythmia requiring urgent treatment.
- Interpretation and limitations
- Check rhythm, QRS duration and repolarisation with an appropriate toxicology interpretation. Compare serial recordings when the suspected exposure can evolve. Sodium-channel blockade is a treatment-relevant mechanism; simply applying a routine antiarrhythmic sequence without considering the poison may worsen the problem.
- 03
Blood gas, electrolytes and renal assessment - Why
- Characterise acidosis, perfusion and organ effects of the exposure.
- Interpretation and limitations
- Interpret pH, bicarbonate, lactate and other available measurements with the history. An abnormal anion gap can support a differential but does not identify a single toxin. Trends may be necessary when metabolism is still evolving. Creatinine and electrolyte changes also affect subsequent medicine and fluid decisions.
- 04
Timed concentrations and liver assessment - Why
- Answer specific exposure and treatment questions using appropriate samples.
- Interpretation and limitations
- For possible deliberate self-poisoning, assess paracetamol exposure and use the relevant concentration and timing pathway. Record the sampling time and the reliability of the ingestion time. A broad qualitative toxicology screen has limitations and should not delay treatment of a clinical syndrome or overrule an incompatible examination.
04Treatment approachPreparation, options, escalation and aftercare.
01Immediate responseRestore breathing in suspected opioid poisoningFirst stepAn adult is poorly responsive with slow shallow breathing and a plausible opioid exposure.+
- 1Call for help, open and protect the airway, provide oxygen and support ventilation as required. Check glucose and assess for injury or another cause of reduced consciousness while obtaining intravenous access and monitoring.
- 2Give naloxone according to the emergency protocol and the patient’s dependence risk. The selected adult overdose SmPC range is 400–2,000 micrograms intravenously, with reassessment and repeat doses at 2–3-minute intervals when needed; lower titrated regimens may suit dependence or iatrogenic toxicity.
- 3EscalationAssess the response by breathing and airway protection, not by demanding complete wakefulness or a particular pupil size. Continue ventilatory support while evaluating insufficient response, mixed ingestion and other diagnoses; escalating naloxone must not delay management of persistent respiratory failure.
- 4Anticipate recurrent depression with longer-acting opioids and obtain specialist advice about repeated doses, infusion and observation duration. Record each administration and response so that the next team can estimate the ongoing antagonist requirement.
02Time-sensitive antidoteManage a potentially toxic paracetamol exposureAn adult reports excess paracetamol use or an uncertain ingestion history.+
- 1Establish the exact product, total amount, weight, timing, co-ingestants and whether doses were staggered. Obtain baseline clinical and laboratory assessment and consult the current UK poisoning pathway early when timing or quantity is unreliable.
- 2DefinitiveUse a properly timed plasma concentration with the UK nomogram only for a suitable single acute ingestion. A sample before 4 hours cannot provide the usual definitive risk assessment. For a potentially toxic overdose with uncertain timing or staggered ingestion, start IV acetylcysteine without delay while obtaining urgent toxicology advice; the standard nomogram is unsuitable.
- 3Prescribe the complete locally approved acetylcysteine regimen promptly when treatment is indicated, including immediate treatment for the uncertain-time or staggered overdose described above. Check weight rules, dose units, diluent, infusion durations and actual final volumes. The licensed three-infusion course totals 300 mg/kg over 21 hours; another approved pathway requires its own complete instructions.
- 4Reassess clinical status and the required liver, coagulation and concentration results before ending treatment. Continued infusion or specialist liver-unit discussion may be necessary; the final bag finishing is an administration event, not proof that toxicity risk has resolved.
03Unidentified exposureTreat a changing toxidrome without premature closureAn agitated or obtunded patient has an uncertain substance exposure.+
- 1Use a repeated ABCDE assessment and look for trauma, infection and metabolic illness alongside possible poisoning. Obtain information from the patient, witnesses and available packaging without delaying stabilization or assuming that a claimed street-drug name identifies its contents.
- 2Examine pupils, skin moisture, secretions, bowel and bladder features, temperature and neuromuscular signs. Combine these findings with the ECG and blood gas to form a mechanism-based differential and identify the immediate physiological threat.
- 3Seek current poison-specific guidance for supportive treatment, antidotes, decontamination or enhanced elimination. Activated charcoal is not routine treatment for every ingestion and requires consideration of the substance, timing, airway and aspiration risk.
- 4Reassess the working diagnosis after each new observation or result. Determine observation duration and discharge readiness from expected kinetics, stability, mental state and follow-up needs, including appropriate psychosocial assessment after self-harm.
05Regimens, contraindications and interactionsTreatment details and the circumstances that modify them.
Naloxone for adult opioid overdose
Selected injection SmPC: 400–2,000 micrograms IV initially, with further doses every 2–3 minutes if required by the response. Reconsider the diagnosis if there is no response after a cumulative 10 mg.Titrate to adequate breathing; opioid dependence or iatrogenic toxicity may need a lower-dose local strategy to avoid abrupt withdrawal. Long-acting exposure can require repeated doses or specialist infusion. Pregnancy does not remove the need to treat life-threatening toxicity.
Acetylcysteine: licensed adult three-infusion regimen
IV: 150 mg/kg over 1 hour in 200 mL diluent, then 50 mg/kg over 4 hours in 500 mL, then 100 mg/kg over 16 hours in 1,000 mL; total 300 mg/kg over 21 hours, with a 110 kg dose-weight ceiling.Use actual weight up to the ceiling and the product-approved diluent and preparation chart; final pump volume depends on preparation. Lower body weight or fluid restriction needs an appropriate protocol. Monitor infusion reactions and use laboratory stopping criteria; do not combine parts of alternative regimens.
06Complications, monitoring and follow-upAdverse effects, response and longer-term review.
- Observe breathing and consciousness repeatedly after naloxone, because the response may wear off before the opioid does. The expected exposure, co-ingestants and subsequent clinical course determine the observation plan rather than a universal brief period after awakening.
- Follow ECG, temperature, acid–base status and organ markers when the suspected toxin or evolving findings make them relevant. A changing QRS or rising temperature should trigger action at the time it occurs, not only at a scheduled handover.
- During acetylcysteine, check the infusion identity, rate and patient response at each bag change. Manage a suspected infusion reaction promptly with clinical assessment and the relevant protocol; do not allow an unexplained interruption to leave indicated antidote treatment unfinished.
- Before discharge, establish physiological and biochemical stability, the likelihood of delayed deterioration, capacity and an appropriate psychosocial plan. Reconcile ongoing medicines and explain which symptoms need urgent reassessment after leaving the department.
07Special situationsVariants, exceptions and circumstances that change the usual approach.
Oxygenation and ventilation are different
A patient receiving oxygen can retain carbon dioxide while the saturation looks acceptable. Respiratory depth, rate, airway protection and appropriate gas or capnography assessment help judge whether naloxone and supportive treatment have restored adequate ventilation.
A pattern can evolve
A mixed ingestion can produce apparently conflicting signs, and modified-release absorption can delay peak effects. Repeating examination and reconsidering the mechanism is more reliable than defending the first toxidrome label after new evidence appears.
Antidote arithmetic needs a preparation check
A correct milligram dose does not guarantee a correct infusion. The stock concentration, diluent volume, drug-added volume and pump time must describe the same preparation; independent calculation should check both dose and deliverable rate.
Medical recovery and discharge readiness differ
Resolution of acute toxicity does not settle ongoing self-harm risk, capacity or safeguarding needs. The discharge decision integrates physical stability with the person’s circumstances and a practical plan for subsequent support.
08Common pitfallsFrequent interpretation and management errors.
- 01
Waiting for a urine drug screen before supporting an inadequately ventilating patient reverses the priority between diagnosis and immediate physiological treatment.
- 02
Using pupil size as the sole endpoint for naloxone can produce unnecessary reversal while failing to focus on breathing and airway protection.
- 03
Plotting a staggered paracetamol ingestion on the single-ingestion nomogram can give a false impression that treatment is unnecessary.
- 04
Mixing bag doses or durations from different acetylcysteine protocols can produce an incorrect cumulative dose despite each fragment looking familiar.