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13. Intoxication and overdoses


Intoxication may be defined as the intake of a quantity of a substance which exceeds the individual's tolerance and produces behavioural or physical abnormalities.


Overdose may be defined as the state that occurs when a person has ingested a drug quantity higher than the recommended therapeutic dose and that also exceeds his/her tolerance.

Note: This section offers some guidelines, basic points and reminders, but is not a comprehensive manual for the management of overdosing and poisonings. When presented with an intoxicated or overdose patient basic ABC procedures should be followed.

In acute overdose it is recommended that patients are closely observed, monitored and referred to an acute care hospital.

A basic modern text on toxicology is Ellenhorn, M. and Barceloux, D.G. Medical toxicology: diagnosis and treatment of human poisoning, Elsevier, New York, 1988.


Clinically obvious alcohol intoxication occurs in non-tolerant individuals at blood alcohol levels of approximately 34 mmol/litre.

In alcohol-dependent persons marked tolerance to the behavioural effects of alcohol may develop. It is not unusual for such patients to appear unimpaired with a blood alcohol level of 60-70 mmol/litre.

Coma develops in most individuals when a blood alcohol level is 90-120 mmol/litre. If the blood alcohol level is less than 100 mmol/litre with a patient in coma or unconscious, another drug, concurrent brain injury or other disease should be suspected.




Methanol is used in some industrial processes. It is not the same as methylated spirits which in Australia is 95% ethanol and only up to 5% methanol as a denaturant. Methanol is a potential killer and those who survive may become blind, as the metabolites of methanol are particularly toxic to the optic nerve.

Toxicity is related to two factors:

Initially central confusion and blindness may occur and it may then be too late for effective treatment. Early recognition and treatment is, therefore, very important.

A lethal dose of methanol varies from person to person. A dose of more than 30 mL of absolute methanol is regarded as potentially lethal.



Intermittent or dependent narcotic users are prone to accidental overdose because they often overestimate their own tolerance or are unaware of the potency of the drug they use.



Overdose with salicylates alone or as a polydrug is common in chronic drug abusers.



The use of the tricyclic antidepressants is common by those involved with drugs of abuse. This drug in large dosage can cause coma, cardiac arrhythmias and anti-cholinergic effect; mortality risk is high.



Many drugs used recreationally can produce psychosis when taken in high doses. Any user showing psychosis requires a detailed assessment.

Clinical features

Drug-induced psychosis is characterised by:

Predisposing, precipitating and perpetuating factors of drug psychosis


There is a medical emergency which requires detailed assessment. Danger to oneself and others needs to be determined. The more disorganised and bizarre the person is, the greater the risk.

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