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.

Management

• Forced intravenous fluids and where necessary diuretic therapy and alkalinisation
• Haemodialysis may be necessary
  
• No treatment options have been shown to be more effective than supporting the airway, respiration, circulation and renal function
• Alkalinisation of the urine is useful with phenobarbital and barbital overdose
  
• Requires the support of an intensive care unit if airway support is required.

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:

• oxidation of methanol by alcohol dehydrogenase to formaldehyde and formic acid
• severe metabolic acidosis.

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.

Management

• Block metabolism of methanol. This is achieved by the administration of ethanol which preferentially saturates the alcohol dehydrogenase pathway in the liver. In most cases ethanol can be given orally or via a gastric tube. An initial dose of 0.6-1.00 gram/kilogram as absolute alcohol should be given (this would be equivalent to 50-87.5 mL of absolute alcohol for a 70 kilogram person).

  When ethanol is given intravenously a similar loading dose of 0.6 grams/kilogram is administered over 30 minutes. Absolute alcohol should be diluted to a 15% solution when used in this manner.

• Treat metabolic acidosis by the use of intravenous bicarbonate if necessary.
• Haemodialysis required if the blood methanol level is more than 20 mmol/litre.
• Monitor arterial blood gases, blood methanol and ethanol level on a regular basis. The objective of management is to keep the blood pH normal and blood ethanol level at approximately 25 mmol/litre until methanol has been eliminated.
• The supports of an intensive care unit are required.

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.

• Slow respiration (2-7/minute), usually deep compared with the shallow and more rapid respiration associated with intoxication by barbiturates, etc.
• Pinpoint pupils
  
• Cyanosis, weak pulse, bradycardia
• Possible pulmonary oedema
  
• Twitching of muscles
• Subnormal temperature may occur.

Management

• Naloxone (0.4 mg intravenously) may be repeated in 3 minute intervals as required if respiratory depression occurs. Such patients need to be carefully monitored for the signs of respiratory depression, and repeated.
• Dialysis and stimulants are not indicated.
  
• If pulmonary oedema is present maintain oxygenation by adequate support of ventilation. Frusemide may be required. It is most important to maintain adequate airway, oxygen where necessary, artificial ventilation and cardiac massage. In some cases vasopressor agents may be required.
• Urgent transfer by resuscitation ambulance to an intensive care unit may be required.

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

• Keep the patient under observation if the salicylate level is more than 2 mmol/litre or if a dose is taken of more than 150 mg/kilogram.
  
• Blood levels of 3-4.5 mmol/litre produce mild intoxication.
• 4.5-7.0 mmol/litre produce moderate intoxication.
  
• More than 7.0 mmol/litre produce severe intoxication.

Management

• Supportive therapy is usually sufficient for salicylate concentrations of less than 4 mmol/litre. If concentrations are more 7.0 mmol/litre haemodialysis should be considered.
• Forced intravenous fluids together with diuretic therapy and alkalinisation of urine.
  
• Patients should not be allowed to become acidotic because acidosis causes increased amounts of salicylates to enter cell membranes. Full investigation of electrolytes, blood sugar, salicylate concentrations, blood gases and prothrombin time should be done at regular intervals.
• Aquamephyton 10 mg subcutaneously should be given.
  
• Continue treatment until the salicylate level is less than 2 mmol/litre.

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.

Management

• A cardiac monitor should be used to detect cardiac arrhythmias and these would require treatment according to the evidence of cardiotoxicity.

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

Drug-induced psychosis is characterised by:

• perceptual disturbance
  • hallucinations – visual, auditory or somatic
    
  • unusual sensations or experience of oneself, others or the outside world
    
• thought disorder
  • abnormal thought patterns
    
  • incomplete sentences
    
  • delusions
    
• disorientation in time, place or person
• history and evidence of recent drug use.

• Predisposition to drug psychosis
  • multiple drug use
    
  • family history or personal history of psychotic illness, particularly schizophrenia or bipolar affective disorder
    
  • any compromised cognitive function (eg personal history of head injury or intellectual disability)
    
• Precipitating factors of drug psychosis
  • type of drug
    
  • hallucinogens, eg LSD, magic mushrooms
    
  • psychostimulants
    
  • cannabis
    
  • solvents
    
  • drug use in non-supportive environments
    
• Perpetuating factors which may lead to drug psychosis
  • further drug use in hospital, eg drugs provided by visitors
    
  • concurrent drug withdrawal.

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.

• Admit, observe and detain if necessary in a secure environment.
• May require psychiatric management, preferably in hospital with good medical facilities.
  
• Detailed drug-use history is needed from collateral informants and patient
• Major tranquillisers are needed (eg 5-10 mg intramuscular haloperidol immediately. This can be repeated half hourly/hourly for 4 doses). Expert reassessment will be required.
  
• Unpredictability of patient behaviour is characteristic and is the feature which poses significant risk. Quite sudden, unexpected serious suicidal behaviour or aggressive behaviour can occur, eg jumping out of a window. Unprovoked attacks on staff or other people, although rare, can occur.
• Occasionally a patient may have a mixed picture 24-72 hours after admission, eg alcohol or benzodiazepine withdrawal may emerge as drug psychosis is settling. This should be anticipated especially in polydrug use.
  
• Detoxification may need to follow, and options need to be discussed with the patient.
• In the long term: develop a management plan, especially for patients with dual diagnosis (eg schizophrenia and heroin dependence).