Forensic Medicine and Toxicology
General Toxicology
General toxicology for MBBS: types of poisoning, decontamination, antidotes and enhanced elimination, viscera preservation and medico-legal duties, mapped to NMC codes FM8.1 to FM8.10.
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General Toxicology
General toxicology for MBBS: types of poisoning, decontamination, antidotes and enhanced elimination, viscera preservation and medico-legal duties, mapped to NMC codes FM8.1 to FM8.10.
General toxicology gives the framework for every specific poison that follows. It defines poison and the types of poisoning, sets out the pillars of management from decontamination to antidotes and elimination, and covers the medico-legal duties, the poisoning autopsy and the correct preservation and dispatch of viscera.
High-yield: General Toxicology
- A poison is any substance that, when introduced into the body, can cause harm or death by its own action.
- Fulminant poisoning kills rapidly from a massive dose, while chronic poisoning results from repeated small doses over time.
- Cumulative poisons such as arsenic, lead and mercury are absorbed faster than they are excreted and build up in the body.
- The four pillars of poisoning management are decontamination, supportive care, antidotes and enhanced elimination.
- Gastric lavage is avoided in corrosive and hydrocarbon ingestion because of the risk of perforation and aspiration.
- Activated charcoal binds many poisons but does not bind metals, alcohols, corrosives, cyanide or lithium.
- Enhanced elimination methods include forced alkaline diuresis, haemodialysis and haemoperfusion for selected poisons.
- In a suspected homicidal poisoning the doctor has a medico-legal duty to inform the police and preserve samples.
- At autopsy, viscera for chemical analysis are preserved in saturated common salt, not in formalin, which interferes with analysis.
- The standard viscera for a poisoning autopsy are stomach with contents, small intestine, liver, kidney and blood, kept in separate containers.
- A separate control container of the preservative is always dispatched with the viscera to the laboratory.
- Aluminium phosphide and organophosphate compounds are among the commonest fatal poisons in India.
- The idea of a corpus delicti reminds the court that poisoning must be proven, not merely suspected, by chemical and clinical evidence.
- Diagnosis of poisoning in the living rests on the history, the clinical toxidrome, bedside tests and laboratory confirmation.
- A toxidrome is a recognisable cluster of signs, such as the cholinergic toxidrome of organophosphates, that points to a class of poison.
The four pillars of poisoning management
- **Decontamination:** Remove the poison: skin washing, gastric lavage where safe, activated charcoal. Avoid lavage in corrosives and hydrocarbons.
- **Supportive care:** Airway, breathing, circulation and treatment of seizures and arrhythmias.
- **Antidotes:** Specific agents such as atropine for organophosphates and N-acetylcysteine for paracetamol.
- **Enhanced elimination:** Forced alkaline diuresis, haemodialysis and haemoperfusion for suitable poisons.
NMC competencies in this chapter
- **FM8.1:** History and evolution of toxicology
- **FM8.2:** Core terms: poison, forensic toxicology and clinical toxicology
- **FM8.3:** Poison classes, kinetics, dynamics and diagnosis
- **FM8.4:** Current poison law and medico-legal duties
- **FM8.5:** Poisoning autopsy and viscera dispatch
- **FM8.6:** Common poisoning patterns in India
- **FM8.8:** Treatment framework: decontamination, support, antidote and elimination
- **FM8.10:** Analytical toxicology methods
Frequently Asked Questions
What are the four pillars of poisoning management?
Decontamination to remove the poison, supportive care to keep the patient alive, specific antidotes where available, and enhanced elimination such as dialysis for selected poisons.
Why is common salt, not formalin, used to preserve viscera for poison analysis?
Saturated common salt preserves tissue without altering the poison, while formalin can react with or mask several poisons and interferes with the chemical analysis.
Which substances are not bound by activated charcoal?
Metals, the alcohols, corrosive acids and alkalis, cyanide and lithium are poorly adsorbed, so charcoal is not useful for these.
What is a toxidrome?
It is a recognisable cluster of signs pointing to a class of poison, such as the cholinergic toxidrome of salivation, lacrimation and small pupils seen in organophosphate poisoning.
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