Toxicology Antidote Reference
Select toxin/poison to view antidote and dosing. Always confirm with Poisons Information Service (UK: 0344 892 0111 / TOXBASE).
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Clinical toxicology antidote reference is a systematic framework used by emergency medicine physicians, pharmacists, and poison control specialists to rapidly identify and administer the correct antidote for acute poisoning. While most poisoning cases are managed with supportive care, a subset of toxidromes have specific, life-saving antidotes that act by reversing receptor binding, neutralising the toxin, or accelerating its metabolism. Delay in antidote administration in these cases can result in death or permanent organ damage. Key antidote pairs include: opioids reversed by naloxone; benzodiazepine respiratory depression reversed by flumazenil; beta-blocker toxicity treated with glucagon and high-dose insulin-euglycaemia; organophosphate/carbamate poisoning treated with atropine plus pralidoxime (2-PAM); cyanide poisoning treated with hydroxocobalamin; methanol and ethylene glycol poisoning treated with fomepizole (alcohol dehydrogenase inhibitor) and ethanol; tricyclic antidepressant (TCA) poisoning treated with sodium bicarbonate; and carbon monoxide poisoning treated with 100% high-flow oxygen or hyperbaric oxygen (HBO). Additional important pairs include: acetaminophen toxicity with N-acetylcysteine (NAC); digoxin toxicity with digoxin-specific antibody fragments (Fab); iron poisoning with deferoxamine; lead poisoning with DMSA or EDTA; warfarin with vitamin K and FFP; heparin with protamine sulphate; and dabigatran with idarucizumab. Poison control centres are an invaluable real-time resource for unusual or complex poisoning scenarios.
Antidote selection = clinical toxidrome identification → confirm poison class → administer specific antidote at correct dose; Naloxone: 0.4–2 mg IV/IM/IN q2–3min (max 10 mg); Atropine: 2–4 mg IV q5–10min until secretions dry; Hydroxocobalamin: 5 g IV over 15 min; Fomepizole: 15 mg/kg loading dose IV; Sodium bicarbonate: 1–2 mEq/kg IV bolus for QRS >100 ms (TCA); N-acetylcysteine: 150 mg/kg IV over 1h loading dose
- 1Identify the clinical toxidrome by examining vital signs, pupil size, level of consciousness, skin findings, and bowel sounds: opioid (miosis, bradypnoea, coma); sympathomimetic (mydriasis, tachycardia, diaphoresis); cholinergic/SLUDGE (salivation, lacrimation, urination, defecation, GI cramps, emesis); anticholinergic (mydriasis, dry skin, hyperthermia, urinary retention, delirium).
- 2Contact the regional Poison Control Centre immediately for guidance in complex, mixed, or unusual poisoning — provide the exact substance, estimated dose, time of ingestion, and patient weight.
- 3Confirm the likely poison class from clinical presentation, collateral history, circumstantial evidence (empty pill bottles, drug paraphernalia, work exposure), and initial investigations (ECG, blood glucose, VBG, anion gap, osmolal gap, paracetamol and salicylate levels).
- 4Initiate immediate resuscitation (airway, breathing, circulation, decontamination where appropriate) while simultaneously preparing the specific antidote.
- 5Administer the antidote at the correct dose and route: titrate naloxone to adequate respiration (not full reversal — this precipitates opioid withdrawal and agitation); give atropine until secretions dry (not until heart rate increases); dose hydroxocobalamin 5 g for suspected cyanide toxicity.
- 6Monitor for antidote-specific complications: flumazenil can precipitate refractory benzodiazepine withdrawal seizures in dependent patients; naloxone has a shorter half-life than most opioids and must be re-dosed or administered as an infusion; fomepizole must continue until methanol/ethylene glycol is metabolised.
- 7Arrange ICU admission for most serious poisonings, even after antidote administration, because secondary organ damage (cardiac, hepatic, renal) may evolve over 12–72 hours after the initial toxin exposure.
Fentanyl and long-acting opioids (methadone, extended-release morphine) may require repeated naloxone doses or infusion.
Naloxone is a competitive opioid receptor antagonist with a half-life of 30–90 minutes — shorter than most opioids; re-sedation is a major risk requiring observation for 4–6 hours minimum.
Atropine treats muscarinic effects; pralidoxime reactivates acetylcholinesterase before 'aging' occurs (within 24–48h for most agents).
Large doses of atropine (sometimes >100 mg in severe cases) may be required to dry secretions; the endpoint is not heart rate but resolution of bronchorrhoea and bronchospasm.
Methanol is metabolised to formic acid by alcohol dehydrogenase — fomepizole blocks this conversion, preventing blindness and death.
An elevated osmolal gap with severe anion gap acidosis is the hallmark of toxic alcohol poisoning; fomepizole is the definitive antidote but must be started early before metabolic acidosis becomes severe.
Serum alkalinisation reverses TCA sodium channel blockade by reducing tricyclic binding and improving cardiac conduction.
QRS >100 ms in TCA overdose predicts ventricular arrhythmia; sodium bicarbonate corrects the physiology by alkalinising serum and providing sodium to overcome channel blockade — never use procainamide or flecainide.
Emergency department nurses use antidote reference charts at the bedside to rapidly prepare naloxone, atropine, and NAC drips when toxicological emergencies are declared., representing an important application area for the Toxicology Antidote in professional and analytical contexts where accurate toxicology antidote calculations directly support informed decision-making, strategic planning, and performance optimization
Hospital pharmacists maintain a STAT antidote kit with pre-stocked hydroxocobalamin, fomepizole, digoxin Fab, and protamine to ensure availability within minutes of a toxicology emergency., representing an important application area for the Toxicology Antidote in professional and analytical contexts where accurate toxicology antidote calculations directly support informed decision-making, strategic planning, and performance optimization
Poison Control Centres provide real-time guidance on antidote selection, dosing, and contraindications for clinicians managing complex or unusual poisoning cases nationwide., representing an important application area for the Toxicology Antidote in professional and analytical contexts where accurate toxicology antidote calculations directly support informed decision-making, strategic planning, and performance optimization
Pre-hospital paramedics carry naloxone for opioid overdose reversal in the community, and many jurisdictions have implemented take-home naloxone programmes for people at risk., representing an important application area for the Toxicology Antidote in professional and analytical contexts where accurate toxicology antidote calculations directly support informed decision-making, strategic planning, and performance optimization
Medical educators use antidote pair mnemonics and simulation scenarios to train emergency medicine registrars on toxidrome recognition and time-critical antidote administration., representing an important application area for the Toxicology Antidote in professional and analytical contexts where accurate toxicology antidote calculations directly support informed decision-making, strategic planning, and performance optimization
Polysubstance overdose — unclear toxidrome
{'title': 'Polysubstance overdose — unclear toxidrome', 'body': 'Many overdose presentations involve multiple substances, producing mixed toxidromes that complicate antidote selection. A systematic approach is essential: secure the airway first, measure blood glucose, obtain a 12-lead ECG (QRS, QTc intervals), check paracetamol and salicylate levels in all overdoses, and perform urine toxicology. Contact Poison Control for complex presentations.'}
Neonatal opioid withdrawal — not treated with naloxone
{'title': 'Neonatal opioid withdrawal — not treated with naloxone', 'body': 'Naloxone is contraindicated in neonates of opioid-dependent mothers because it precipitates acute opioid withdrawal, which can be fatal in neonates. Neonatal opioid withdrawal syndrome (NOWS) is managed with morphine or methadone taper, supportive care, and rooming-in with the mother. Naloxone should only be used in neonates with acute iatrogenic opioid respiratory depression after a one-off exposure.'}
Extremely large or small input values in the Toxicology Antidote may push
Extremely large or small input values in the Toxicology Antidote may push toxicology antidote calculations beyond typical operating ranges. While mathematically valid, results from extreme inputs may not reflect realistic toxicology antidote scenarios and should be interpreted cautiously. In professional toxicology antidote settings, extreme values often indicate measurement errors, unusual conditions, or edge cases meriting additional analysis. Use sensitivity analysis to understand how results change across plausible input ranges rather than relying on single extreme-case calculations.
Delayed toxicity — acetaminophen staggered overdose
{'title': 'Delayed toxicity — acetaminophen staggered overdose', 'body': 'Staggered or repeated supratherapeutic acetaminophen ingestion (e.g., over several days for pain) may not follow the standard Rumack-Matthew nomogram because the timing of ingestion is uncertain. In these cases, treat empirically with a full NAC course if any concern exists; the nomogram cannot be reliably applied, and elevated ALT with hepatotoxicity risk should trigger treatment regardless of serum paracetamol level.'}
| Toxin/Class | Antidote | Dose | Mechanism |
|---|---|---|---|
| Opioids | Naloxone | 0.4–2 mg IV q2–3min | Competitive opioid receptor antagonist |
| Benzodiazepines | Flumazenil (rarely used) | 0.2 mg IV q1min to max 1 mg | GABA-A competitive antagonist |
| Organophosphates | Atropine + Pralidoxime | Atropine 2–4 mg IV; 2-PAM 1–2 g IV | Muscarinic blockade; AChE reactivation |
| Cyanide | Hydroxocobalamin | 5 g IV over 15 min | Binds cyanide → cyanocobalamin |
| Methanol/Ethylene glycol | Fomepizole | 15 mg/kg IV loading | Inhibits alcohol dehydrogenase |
| Carbon monoxide | 100% O₂ / HBO | NRB mask or 2–3 ATA HBO | Displaces CO from haemoglobin |
| TCAs | Sodium bicarbonate | 1–2 mEq/kg IV bolus | Serum alkalinisation reverses Na⁺ channel blockade |
| Paracetamol | N-acetylcysteine | 150 mg/kg IV over 1h | Glutathione replenishment |
| Digoxin | Digoxin-specific Fab | 10–20 vials IV | Antibody binding of free digoxin |
| Heparin | Protamine sulphate | 1 mg per 100 IU heparin | Ionic binding inactivates heparin |
| Iron | Deferoxamine | 15 mg/kg/h IV infusion | Chelation of free iron |
| Beta-blockers/CCBs | High-dose insulin + glucagon | Insulin 1 U/kg/h; Glucagon 3–5 mg IV | Myocardial inotropy |
Why is flumazenil rarely used in benzodiazepine overdose?
Flumazenil reverses benzodiazepine-induced sedation but is contraindicated in benzodiazepine-dependent patients (precipitates severe withdrawal seizures), in mixed overdoses with TCAs (seizures may be unmasked), and in patients with raised intracranial pressure. Most benzodiazepine overdoses are managed with supportive airway management rather than flumazenil. This is particularly important in the context of toxicology antidote calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise toxicology antidote computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
What is the antidote for acetaminophen (paracetamol) poisoning?
N-acetylcysteine (NAC) is the definitive antidote, effective at replenishing hepatic glutathione and preventing the toxic NAPQI metabolite from causing hepatocellular necrosis. NAC is administered IV (21-hour Prescott protocol: 150 mg/kg over 1h, 50 mg/kg over 4h, 100 mg/kg over 16h) or orally. It is most effective within 8 hours of ingestion but has benefit up to 24 hours and beyond in staggered overdose.
How is cyanide poisoning recognised and treated?
Cyanide poisoning presents with rapid loss of consciousness, seizures, lactic acidosis (lactate >8 mmol/L), and cardiovascular collapse — classically in smoke inhalation victims or those exposed to industrial chemicals. Hydroxocobalamin (5 g IV over 15 min) is the first-line antidote and binds cyanide to form cyanocobalamin (excreted renally). Sodium thiosulphate 12.5 g IV is a second-line agent.
What is high-dose insulin-euglycaemia (HDIE) therapy?
HDIE is used for calcium channel blocker and beta-blocker cardiotoxicity refractory to conventional resuscitation. Insulin at 1–10 U/kg/h (titrated for haemodynamic effect) improves myocardial glucose uptake and inotropy in the setting of toxin-induced myocardial depression. Concurrent 50% dextrose infusion maintains euglycaemia; potassium must be closely monitored. This is particularly important in the context of toxicology antidote calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise toxicology antidote computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
What is the antidote for digoxin toxicity?
Digoxin-specific antibody fragments (Fab — Digibind/DigiFab) are the antidote for life-threatening digoxin toxicity (VF, VT, complete heart block, severe bradycardia, or K+ >5.5 mEq/L with acute toxicity). Dose is empirical (10–20 vials for acute overdose) or calculated from the serum digoxin level and patient weight. This is particularly important in the context of toxicology antidote calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise toxicology antidote computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
When is hyperbaric oxygen (HBO) indicated for carbon monoxide poisoning?
HBO at 2–3 atmospheres accelerates CO elimination (reduces half-life from ~4 hours on room air to ~20 minutes) and is indicated for: COHb >25%, loss of consciousness, neurological symptoms (confusion, syncope), cardiac abnormalities, or pregnant patients with any COHb >15%. HBO may reduce the incidence of delayed neuropsychiatric syndrome. This is particularly important in the context of toxicology antidote calculations, where accuracy directly impacts decision-making. Professionals across multiple industries rely on precise toxicology antidote computations to validate assumptions, optimize processes, and ensure compliance with applicable standards. Understanding the underlying methodology helps users interpret results correctly and identify when additional analysis may be warranted.
What is the antidote for heparin overdose?
Protamine sulphate reverses heparin anticoagulation. Dose: 1 mg protamine per 100 units of heparin given in the last 2–3 hours (max 50 mg IV, given slowly at <5 mg/min). Adverse reactions include hypotension, bradycardia, and anaphylaxis — especially in patients with prior fish allergy or protamine-containing insulin. Protamine only partially reverses LMWH and has no effect on fondaparinux.
How is iron poisoning treated?
Deferoxamine is the antidote for severe iron poisoning (serum iron >90 µmol/L or >500 µg/dL, symptomatic toxicity, or shock). It chelates free iron to form ferrioxamine excreted in urine (urine turns 'vin rosé' colour). Deferoxamine infusion should be continued until the patient is clinically stable and ferrioxamine production has ceased.
Pro Tips
Memorise the osmolal gap formula for toxic alcohol poisoning: Osmolal Gap = Measured Osmolality − Calculated Osmolality, where Calculated Osmolality = 2×Na + Glucose/18 + BUN/2.8. A gap >10 mOsm/kg in the context of anion gap metabolic acidosis strongly suggests methanol or ethylene glycol poisoning — start fomepizole before confirmatory levels are available.
Visste du?
Hydroxocobalamin — the cyanide antidote — is essentially a form of vitamin B12. Its vivid red colour, harmlessly excreted in urine, explains why patients' skin and urine turn red after administration. The visual effect has occasionally been mistaken for haematuria by nursing staff unfamiliar with the treatment.
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