Chapter 31: General Principles of Forensic Toxicology

**Toxicology**

The branch of medicine that deals with properties, action, toxicity and lethal dose, estimation of, treatment and autopsy findings of poisons.

**Forensic toxicology**

deals with medical and legal aspects of the harmful effects of the chemicals on the human body.

**Clinical toxicology**

refers to human diseases caused by or associated with abnormal exposure to chemical substances.

**Toxinology**

refers to toxins produced by living organisms, which are dangerous to man, e.g. venom of snakes, spiders and bees, bacterial and fungal toxins, poisonous plants, etc.

**Drugs**

natural or synthetic substances, which are used to exert physiological or psychological effect on the consumer.

Drugs

natural or synthetic substances, which are used to exert physiological or psychological effect on the consumer.

**Poison**

any substance which when administered by any route can cause disease, deformity or death.

**Overdose**

an intentional toxic exposure.

**Locally acting poisons**

These act only at the site of application such as skin/mucosa, e.g. corrosive poisons

**Remotely acting poisons**

These act only after being absorbed into the circulatory system, e.g. narcotic poisons, cardiac poisons, etc.

Idiosyncrasy

• It means unexpected allergy or intolerance.

• It brings about untoward effects or ill health or death, e.g. allergy to certain drugs like penicillin, certain foodstuffs like eggs, shellfish, etc.

**Epidemiology**

the study of the distribution and determinants of health-related states and events in populations and the control of health problems, the study of epidemic disease.

**Epidemiology**

It refers to the field of medicine concerned with the determination of causes, incidence, and characteristic behavior of disease outbreaks affecting human populations and includes the interrelationships of host, agent, and environment as related to the distribution and control of disease.

Toxic epidemiology

the study of the distribution and determinants of health related states and events in populations, and the control of poisoning related health problems.

**Occupational toxicology**

deals with the chemicals found in the workplace.

**Environmental toxicology**

deals with the potentially deleterious impact of chemicals, present as pollutants of the environment, to living organisms.

**Ecotoxicology**

a specialized area of environmental toxicology dealing with effects of pollutants on population dynamics in an ecosystem.

**Environment**

includes all the surroundings of an individual organism, but particularly the air, soil, and water.

**Pollutant**

a substance that occurs in the environment, at least in part as a result of human activity, and which has a deleterious effect on living organisms.

**Air pollution**

product of industrialization, technological and biological development, increased urbanization and indoor sources

**Toxicity**

the ability of a chemical agent to cause injury. It is a qualitative term. Whether these injuries occur depends on the amount of chemical absorbed.

**Hazard**

the likelihood that injury will occur in a given situation or setting, the conditions of use and exposure are primary considerations.

**Risk**

the expected frequency of the occurrence of an undesirable effect arising from extrapolation from the observed relationships to the expected responses at doses occurring in actual exposure situations

**Carbon monoxide**

a colorless, tasteless, odorless, and nonirritating gas, a by product of incomplete combustion.

**Sulfur dioxide**

a colorless, irritant gas generated primarily by the combustion of sulfur containing fossil fuels.

**Nitrogen dioxide**

a brownish irritant gas sometimes associated with fires. It is also formed from fresh silage; exposure of farmers to NO2 in the confines of a silo can lead to “silo filler’s disease.”

**Ozone**

a bluish irritant gas that occurs normally in the earth’s atmosphere, where it is an important absorbent of ultraviolet light.

Chlorinated Hydrocarbon Insecticides

• These agents are usually classified into four groups: chlorophenothane, benzene hexachlorides, cyclodienes, and toxaphenes.

• They are aryl, carbocyclic, or heterocyclic compounds containing chlorine substituents.

Benzene

It is widely used for its solvent properties and as an intermediate in the synthesis of other chemicals.

**Organophosphorus Insecticides**

They are useful pesticides when in direct contact with insects or when used as ‘plant systemics’, where the agent is trans-located within the plant and exerts its effects on insects that feed on the plant.

**Carbamate Insecticides**

These compounds inhibit acetylcholinesterase by carbamylation of the esteratic site.

**Botanical Insecticides**

These insecticides derived from natural sources include nicotine, rotenone, and pyrethrum

**Paraquat**

The most important agent of **Bipyridyl Herbicides.**

**Decontamination**

refers to skin/eye decontamination, gut evacuation and administration of activated charcoal.

**Activated charcoal**

a black slurry material, which owing to its large surface area is highly effective at adsorbing many toxins.

Medicoal

an effervescent preparation containing sodium citrate and povidone and must be mixed with water before use.

**Catharsis**

 known to reduce the transit time of drugs in the gastrointestinal tract.

**Ionic/ Saline Cathartics**

These cathartics alter the physicochemical forces within the intestinal lumen leading to osmotic retention of fluid which activates motility reflexes and enhances expulsion.

**Saccharides cathartics**

This consists of giving sorbitol (D-glucitol), which is the cathartic of choice in an adult because of its better efficacy than saline cathartics.

**Whole bowel irrigation**

Involves administration of non-absorbable polyethylene glycol solution to cause a liquid stool and reduce drug absorption by physically forcing gastrointestinal contents.

**Diaphoresis**

It means inducing excessive perspiration, and poison is excreted through sweat.

**Antidotes**

substances, which, on administration counteract or neutralize the effect of a poison.

**Physical/ Mechanical Antidotes**

These neutralize the poison by their mechanical action.

**Chemical Antidotes**

These acts by forming new compounds with the poison, which will be either nontoxic or less active or insoluble.

**Universal Antidote**

 It is an antidote, which is a combination of physical and chemical antidote. It can be administered, when the exact nature of poison taken is not known or when one or more poison is/are taken.

**Physiological/Pharmacological Antidotes**

These act by producing exactly the opposite action to those produced by the poison.

**Chelating Agents**

These are true physiological agents which act by forming stable and soluble complexes by the inner ring structure which can combine with the poison molecules easily.

**British Anti-Lewisite**

a colorless liquid in peanut oil, given deep intramuscularly.

**Ethylene diamine tetra-acetic acid**

it is rarely used in heavy metallic poisoning, as it is prone to remove blood and bone calcium also producing fatal hypocalcaemia.

**Penicillamine**

it is obtained by hydrolytic dehydration of penicillin. It is well absorbed from the gastrointestinal tract.

**Deferoxamine**

• a water soluble compound with great affinity for ferric iron.

• It is administered in a dose of 8 gm in 50 to 200 ml of water given orally or by nasogastric tube, 1-2 gm intravenously or intramuscularly 4 hourly for 2 days.

**Traditional wet chemistry**

This comprises a painstaking testing and retesting of unknown material using different reagents, until the composite behavior patterns give a clue to the identity of the material/ poison.

**Wet chemistry**

Refers  to the analytical techniques in which various chemical reagents, such as acids, bases and salts are applied to a sample, identified on the basis of its reactions with the reagents.

Analytical toxicology services

These services can be provided in clinical biochemistry laboratories that serve a local hospital or accident and emergency unit.

**Qualitative Tests**

This includes certain biochemical tests wherein the nature of the poison is identified using the biological material samples from the victim of poisoning are in common practice.

**Quantitative Analytical Methods**

This comprises methods where in the tests are done not only to exactly identify the poison but also to estimate the concentration of the poison in the body of the poisoned victim.

Glasgow Coma Scale

The ______ is the most frequently used in assessment of the degree of impaired consciousness, though remarkably it has never been validated for use in poisoned patients.

Gastric Lavage

It should only be undertaken if patient has ingested a potentially life-threatening amount of a poison and presents within 1 hour of the ingestion.

Trinder’s Test

This color test uses *Salicylic acid & Acetyl salicylic acid*.

FPN Test

This color test uses *Phenothiazines.*

Forrest test

This color test uses *Imipramine and related compounds*

Fujiwara test

This color test uses *Trichloro compounds, including chloral hydrate, chloroform, dichloral phenazone and Trichloroethylene.*

O-cresol/ammonia test

This color test uses *Paracetamol, Phenacetin*

Dithionite test

This color test uses *Paraquat, diquat*

Dichromate test

This color test uses *Ethanol and other volatile reducing agents*

Diphenylamine test

This color test uses *Chlorates and other oxidizing agents*

Ferricyanide/ ferrocyanide test

This color test uses *Ferrous and Ferric Iron*

Meixner test

This color test uses *Poisonous mushroom*

Reinsch test

This color test uses *Arsenic, antimony, bismuth and mercury*

Marquis’ reagent test

This color test uses *Morphine and other opium*