Any substance which, if absorbed by, introduced into or applied to a living organism, may cause illness or death. The term ‘toxin’ is often used to refer to a poison of biological origin. The study of the effects of poisons is known as toxicology.
The concept of the dose-response is important for understanding the risk of exposure to a particular substance. This is embodied in a statement by Paracelsus (c.1493–1541): ‘All substances are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy.’
Poisoning may occur in a variety of ways: deliberate – SUICIDE, substance abuse or murder; accidental – including accidental overdose of medicines; occupational; and environmental – including exposure during fire.
Ingestion is the most common route of exposure, but poisoning may also occur through inhalation, absorption through the skin, by injection and through bites and stings of venomous animals. Poisoning may be acute, where a single exposure produces clinical effects with a relatively rapid onset; or chronic, where prolonged or repeated exposures may produce clinical effects which may be insidious in onset, cumulative and in some cases permanent.
Diagnosis of poisoning is usually by circumstantial evidence or elimination of other causes of the clinical condition of the patient. Some substances (e.g. opioids) produce a characteristic clinical picture in overdose that can help with diagnosis. In some patients, laboratory analysis of body fluids or the substance taken may be useful to determine or confirm the offending agent. Routine assays are not necessary. For a very small number of poisons, such as paracetamol, aspirin, iron and lead, the management of the patient may depend on measuring the amount of poison in the bloodstream.
In the UK, the most common agents involved in intentional or accidental poisoning are ANALGESICS, ANTIDEPRESSANT DRUGS and SEDATIVES. Alcohol is also commonly taken by adults, usually in combination with drugs. Children may swallow household cleaners, white spirit, plant material – such as belladonna (deadly nightshade) and certain mushrooms; for example, death cap and fly agaric – aftershave and perfume as well as drugs. The use of child-resistant containers has reduced the number of admissions of children to hospital for treatment. If possible, the suspect container, drug or plant should be taken with the victim to the hospital or doctor.
of poisoning usually begins with decontamination procedures. For ingested substances this may involve making the patient sick or washing the stomach out (GASTRIC LAVAGE): this is usually only worthwhile if performed soon after ingestion. Salt water must never be given to induce vomiting as this procedure is potentially dangerous. For substances spilt on the skin, the affected area should immediately be thoroughly washed and all contaminated clothing removed. Following eye exposure, the affected eye/s should be thoroughly irrigated with saline or water.
Treatment thereafter is generally symptomatic and supportive, with maintenance of the victim's respiratory, neurological and cardiovascular systems and, where appropriate, monitoring of their fluid and electrolyte balance and liver and kidney function. There are specific antidotes for a few substances: the most important of these are PARACETAMOL, iron, cyanide (see CYANIDE POISONING), opioids (see OPIOID), DIGOXIN and some insecticides. Heavy-metal poisoning is treated with CHELATING AGENTS – chemical compounds that form complexes by binding metal ions, such as desferrioxamine and penicillamine.
The National Poisons Information Service provides a primary toxicology database to clinicians whose employing authority has registered with it. Its website provides information about routine diagnosis, treatment and management of people exposed to drugs, household products and industrial and agricultural products.
(See also APPENDIX 1: BASIC FIRST AID.)