Q1 LONG ANSWER 10M ★ High-yield

Define poison. Describe the classification of poisons, the factors modifying their action and the laws relating to them.

Forensic Medicine · 2nd Professional — Para-Clinical

Definitions

A poison is any substance which, when administered, inhaled, ingested or applied to the body in relatively small quantities, is capable of producing ill health or death by its local or constitutional effects, or both.

There is NO absolute distinction between a poison, a drug and a food. The distinction is one of dose, and this is the governing principle of the whole subject, expressed by paracelsus as "sola dosis facit venenum" — only the dose makes a thing a poison. Water, oxygen and common salt all kill in sufficient quantity, and arsenic and digitalis are medicines in small ones
Toxicology is the science of poisons — their source, physical and chemical properties, mode of action, fatal dose and fatal period, symptoms, treatment, postmortem appearances, tests and the legal aspects. forensic toxicology is the part concerning the courts
Fatal dose is the smallest amount likely to cause death, and fatal period the shortest time in which death usually occurs. Both are approximations only, derived from reported cases, and both vary enormously with the factors set out below — so neither should ever be stated as a fixed figure in evidence

Classification

Class	Subdivisions and examples
I. Corrosives	Strong acids — mineral (sulphuric, nitric, hydrochloric) and organic (carbolic, oxalic, acetic, salicylic); strong alkalis — hydroxides and carbonates of sodium, potassium and ammonium
II. Irritants	Inorganic — non-metallic (phosphorus, chlorine, bromine, iodine) and metallic (arsenic, lead, mercury, copper, zinc, antimony). Organic — vegetable (abrus, castor, croton, Calotropis, marking nut) and animal (snake, scorpion, cantharides). Mechanical — powdered glass, chopped hair, diamond dust
III. Neurotics — acting on the nervous system	Cerebral: somniferous (opium and its alkaloids), inebriant (alcohol, ether, chloroform), deliriant (datura, cannabis, belladonna, cocaine). Spinal: excitant (strychnine, nux vomica), depressant (gelsemium). Peripheral: conium, curare
IV. Cardiac poisons	Aconite, oleander (yellow and white), digitalis, nicotine, quinine
V. Asphyxiants	Carbon monoxide, carbon dioxide, hydrogen sulphide, cyanide, and war gases
VI. Miscellaneous	Analgesics and antipyretics, sedatives, insecticides (organophosphates), rodenticides (aluminium phosphide), and food poisoning

Other classifications — by origin (mineral, vegetable, animal, synthetic); by mode of action (local, remote, or both); and, most usefully in practice, by the medicolegal manner — homicidal, suicidal, accidental, abortifacient, stupefying, cattle poison, and those used for malingering

CLINICAL PEARL

The dose is the whole of toxicology, and the classification is a filing system rather than a law of nature. Botulinum toxin is the most poisonous substance known and is injected into faces weekly; digitalis treats heart failure and kills; water in excess causes fatal hyponatraemia. A substance is not "a poison" — a quantity of it, by a route, in a person, is poisonous, and every question in a poisoning case reduces to those four variables.

Factors Modifying the Action of a Poison

Factor	Effect
Dose	The most important factor. A large dose may act more slowly by causing vomiting which expels it, or by delaying absorption; and a small repeated dose may kill by cumulation
Form and physical state	Gases act fastest, then liquids, then solids; a substance in solution acts faster than a tablet; a fine powder faster than a coarse one; an insoluble compound may be inert (barium sulphate is harmless while barium carbonate is lethal)
Route of administration	In descending order of speed: inhalation and intravenous, then intramuscular, subcutaneous, oral, rectal, and finally through intact skin. A poison inhaled or injected bypasses the first-pass metabolism of the liver, which is why the oral route is often the safest
Condition of the stomach	An empty stomach absorbs faster; food, and especially fatty food, delays absorption; and gastric disease alters it
Age	Children and the elderly are more susceptible — immature or impaired metabolism, and altered distribution
Body weight and health	The dose per kilogram matters; and hepatic or renal disease markedly increases toxicity by impairing metabolism and excretion
Idiosyncrasy and allergy	An abnormal reaction in a susceptible individual, often genetic — G6PD deficiency with primaquine and sulphonamides, and pseudocholinesterase deficiency with suxamethonium
Tolerance and addiction	An addict may survive many times the ordinary fatal dose of opium or alcohol; and the tolerance is lost rapidly on abstinence, which is why so many overdose deaths occur on release from prison or after detoxification
Cumulation	Where excretion is slower than administration — lead, arsenic, mercury, digitalis and strychnine
Synergism and antagonism	Alcohol greatly potentiates sedatives, opioids and antihistamines; and this combination accounts for a large share of accidental deaths
Sleep and metabolic state	Absorption and metabolism are slower during sleep, so a poison taken at night may act more slowly and be discovered too late

Laws Relating to Poisons

Statute or provision	Content
BNS 123 (formerly IPC 328)	Causing hurt by means of poison or any stupefying, intoxicating or unwholesome drug, with intent to cause hurt or to commit an offence — up to 10 years and fine. The provision covering stupefaction for robbery
BNS 103 (IPC 302) and BNS 105 (IPC 304)	Murder and culpable homicide, where death results
The poisons act 1919 and Rules	Regulates the possession and sale of specified poisons; requires licensing, labelling with the word poison and a skull-and-crossbones, and the maintenance of a sale register
The drugs and cosmetics act 1940 and Rules	Schedule H and H1 drugs to be sold only on the prescription of a registered practitioner, with H1 requiring a separate register kept for 3 years; schedule X for the more strictly controlled; and Schedule G for those needing medical supervision
The NDPS act 1985	Narcotic Drugs and Psychotropic Substances — possession, sale, transport and cultivation; with stringent penalties graded by quantity (small, intermediate and commercial)
The insecticides act 1968	Manufacture, sale, transport and use of insecticides — of great importance in India, where pesticide self-poisoning is a leading cause of suicide, and where restriction of the most toxic compounds has been shown to reduce mortality
Other	The Pharmacy Act 1948; the Drugs and Magic Remedies (Objectionable Advertisements) Act 1954; and the Food Safety and Standards Act 2006

Applied Aspects

Never state a fatal dose as a fixed figure in evidence; it is an approximation from reported cases, and tolerance, route, form, age and health all move it substantially. Give a range and state the qualifications
Ask about tolerance in every opioid or alcohol death; a habituated person survives doses that would kill several others, and the loss of tolerance after abstinence is the classic mechanism of death on release from prison or discharge from a rehabilitation programme
Ask about alcohol in every sedative or opioid case; the synergism is the commonest single contributor to accidental overdose and is routinely omitted from the history
Consider the form as well as the substance; barium carbonate is lethal and barium sulphate is inert, and a report that names the element without the compound may be seriously misleading
Remember the stupefaction provision under BNS 123; travellers on trains and buses in India are regularly robbed after being given food or drink laced with a sedative, and the case is charged under that section
Know which schedule a drug is in before prescribing or dispensing it; Schedule H1 requires a separate register kept for three years, and non-compliance is an offence
Gases act fastest and intact skin slowest, and the inhaled and intravenous routes bypass first-pass metabolism in the liver
An empty stomach absorbs faster, and fatty food delays absorption, which bears on the interval between the meal and the symptoms
Cumulation kills where excretion is slower than intake — lead, arsenic, mercury, digitalis and strychnine are the classical examples
Idiosyncrasy is often genetic — G6PD deficiency with primaquine and pseudocholinesterase deficiency with suxamethonium
A large dose may act more slowly by provoking vomiting that expels it, which is why dose and outcome are not simply proportional
Sale registers under the Poisons Act and the Drugs Rules are frequently the evidence that identifies the purchaser
Insecticide restriction has reduced Indian suicide mortality, and is among the most effective public health measures available
Classify by manner as well as by action; homicidal, suicidal, accidental, abortifacient, stupefying and cattle poisons behave differently
Barium carbonate kills and barium sulphate is inert; naming the element without the compound may be seriously misleading
Tolerance is lost rapidly on abstinence, which is why so many opioid deaths occur on release from prison or after detoxification
Schedule H1 requires a separate register kept three years, and non-compliance is itself an offence
Absorption is slower during sleep, so a poison taken at night may act slowly and be discovered far too late

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