A Textbook of Clinical Pharmacology and Therapeutics

CRIMINALPOISONING 449

Commission on Human Medicines (CHM) has advised that
co-proxamolshould no longer be prescribed. Whilst overdose
from other paracetamol–opioid compounds (e.g. co-codamol)
may also present with coma, pinpoint pupils and hypoventila-
tion, the cardiac toxicity should be markedly reduced.

CARBON MONOXIDE

This is a common cause of fatal poisoning. Carbon monoxide
suicides are usually men under 65 years of age, who die from
carbon monoxide generated from car exhaust fumes (catalytic
converters reduce the carbon monoxide emission and this may
have reduced the number of deaths). Accidental carbon monox-
ide poisoning is also common and should be considered in the
differential diagnosis of confusional states, headache and vom-
iting, particularly in winter as a result of inefficient heaters and
inadequate ventilation. Measurement of the carboxyhaemaglo-
bin level in blood may be helpful. Carbon monoxide toxicity
may also be present in survivors of fires. The immediate man-
agement consists of removal from exposure and administration
of oxygen. There is evidence that hyperbaric oxygen speeds
recovery and reduces neuropsychiatric complications.

ACCIDENTAL POISONING

Accidental poisoning with drugs causes between 10 and 15

deaths per annum in children. Most commonly, tablets were

prescribed to the parents and left insecure in the household

or handbag. Unfortunately, many drugs resemble sweets.

Antidepressants are commonly implicated. The use of child-

proof containers and patient education should reduce the inci-

dence of these unnecessary deaths. Non-drug substances that

cause significant poisoning in children include antifreeze,

cleaning liquids and pesticides.

In adults, accidental poisoning most commonly occurs at

work and usually involves inhalation of noxious fumes.

Factory and farm workers are at particular risk. Carbon

monoxide is associated with approximately 50 accidental

deaths and seriously injures at least 200 individuals in the UK

per year. The onset of symptoms is often insidious. There is

particular concern in the UK about the effect of organophos-

phate pesticides, not only as a cause of acute poisoning, but

also because it is possible that repeated exposure to relatively

low doses may result in chronic neurological effects. Those

working with sheep dip appear to be most at risk.

CRIMINAL POISONING

This is one mode of non-accidental injury of children.

Homicidal poisoning is rare, but possibly underdiagnosed.

There is increasing concern that terrorists may use poisons

such as nerve agents. Cross-contamination is an issue. ‘NAAS

pods’ are available for emergencies. Specialist advice should

be sought from the National Poisons Information Service

(0844 892 0111). Suspicion is the key to diagnosis and toxico-

logical screens are invaluable.

Key points

Diagnosis of acute self-poisoning in comatose patients

• History:
  from companions, ambulance staff, available
  drugs/poisons, suicide note.


• Examination:
  immediate vital signs;
  signs of non-poison causes of coma (e.g. intracerebral
  haemorrhage);
  signs consistent with drug overdose (e.g. meiosis and
  depressed respiration due to opioid).


• Investigation:
  determine severity (e.g. blood gases, ECG);
  determine paracetamol level to determine whether
  acetylcysteine is appropriate;
  exclude metabolic causes of coma (e.g. hypoglycaemia);
  diagnose specific drug/poison levels if this will affect
  management.
  Note: Acute overdose may mimic signs of brainstem death,
  yet the patient may recover if adequate supportive care is
  provided. Always measure the blood glucose concentration
  in an undiagnosed comatose patient.

NON-DRUG POISONS

A vast array of plants, garden preparations, pesticides, house-
hold products, cosmetics and industrial chemicals may be
ingested. Some substances, such as paraquat and cyanides, are
extremely toxic, whilst many substances are non-toxic unless
enormous quantities are consumed. It is beyond the scope of
this book to catalogue and summarize the treatment of all poi-
sons and the reader is strongly advised to contact one of the poi-
sons information services (see Table 54.6 for telephone number)
whenever any doubt exists as to toxicity management.

PSYCHIATRIC ASSESSMENT

It is important to assess the mental state of overdose patients
following recovery. Although most patients take overdoses as
a reaction to social or life events, some overdose patients are
pathologically depressed or otherwise psychiatrically unwell
and should be reviewed by a psychiatrist. In treating depres-
sion decisions regarding drug treatment involve a balance
between the efficacy of the drug and the risk of further over-
dose. Selective serotonin reuptake inhibitors are safer alterna-
tives to tricyclics.

Key points

Symptoms of accidental carbon monoxide poisoning

• Headache, 90%


• Nausea and vomiting, 50%


• Vertigo, 50%


• Alteration in consciousness, 30%


• Subjective weakness, 20%

Source: the Chief Medical Officer.