Pharmacology
Toxicology and Environmental Pharmacology
Toxicology for MBBS and NEET-PG: management of poisoning and specific antidotes including N-acetylcysteine, naloxone, atropine and chelators, mapped to NMC codes.
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Toxicology and Environmental Pharmacology
Toxicology for MBBS and NEET-PG: management of poisoning and specific antidotes including N-acetylcysteine, naloxone, atropine and chelators, mapped to NMC codes.
This chapter covers the principles of toxicology and the management of common poisonings and environmental exposures. It focuses on the specific antidotes and general measures such as decontamination and supportive care that are tested heavily in examinations and are life-saving in practice.
High-yield: Toxicology and Environmental Pharmacology
- Paracetamol overdose causes hepatotoxicity and is treated with N-acetylcysteine, most effective when given early.
- Organophosphate poisoning is treated with atropine to block muscarinic effects and pralidoxime to reactivate the enzyme.
- Opioid overdose causes pinpoint pupils and respiratory depression and is reversed by naloxone.
- Benzodiazepine overdose is reversed by flumazenil, used cautiously to avoid precipitating seizures.
- Methanol and ethylene glycol poisoning are treated with fomepizole or ethanol, which block alcohol dehydrogenase.
- Iron overdose is treated with the chelator desferrioxamine.
- Lead poisoning is treated with chelators such as calcium disodium edetate, dimercaprol or succimer.
- Carbon monoxide poisoning causes tissue hypoxia with a normal oxygen saturation reading and is treated with high-flow oxygen.
- Cyanide poisoning is treated with hydroxocobalamin or sodium thiosulphate with sodium nitrite.
- Digoxin toxicity is reversed by digoxin-specific antibody fragments.
- Warfarin overdose is reversed by vitamin K and, if bleeding, prothrombin complex concentrate.
- Beta blocker and calcium channel blocker overdose may respond to glucagon and calcium respectively.
- Activated charcoal reduces absorption of many ingested poisons if given early.
- Snakebite envenomation is treated with polyvalent antivenom guided by clinical and coagulation signs.
Poisons and their antidotes
- **Paracetamol:** N-acetylcysteine restores glutathione.
- **Organophosphate:** Atropine plus pralidoxime.
- **Opioid:** Naloxone reverses respiratory depression.
- **Iron:** Desferrioxamine chelates excess iron.
NMC competencies in this chapter
- **PH1.51:** Principles of management of poisoning
- **PH1.52:** Specific antidotes for common poisonings
- **PH1.53:** Environmental toxicology and heavy metal poisoning
Frequently Asked Questions
What is the antidote for paracetamol overdose?
N-acetylcysteine, which replenishes glutathione to neutralise the toxic metabolite and is most effective when started early after ingestion.
How is organophosphate poisoning managed?
Atropine is titrated to dry secretions to block muscarinic effects, and pralidoxime reactivates acetylcholinesterase before the enzyme ages.
Why is carbon monoxide poisoning easy to miss?
It binds haemoglobin tightly, causing tissue hypoxia while the standard pulse oximeter still reads a normal oxygen saturation, so the diagnosis needs clinical suspicion.
What reverses digoxin toxicity?
Digoxin-specific antibody fragments bind the drug and are used for life-threatening arrhythmias or severe hyperkalaemia from digoxin overdose.
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