A Textbook of Clinical Pharmacology and Therapeutics

Commission on Human Medicines (CHM) has advised that
co-proxamol should no longer be prescribed. Whilst overdose
from other paracetamol–opioid compounds (e.g. co-codamol)
may also present with coma, pinpoint pupils and hypoventilation,
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 monoxide
poisoning is also common and should be considered in the
differential diagnosis of confusional states, headache and vomiting,
particularly in winter as a result of inefficient heaters and
inadequate ventilation. Measurement of the carboxyhaemaglobin
level in blood may be helpful. Carbon monoxide toxicity
may also be present in survivors of fires. The immediate management
consists of removal from exposure and administration
of oxygen. There is evidence that hyperbaric oxygen speeds
recovery and reduces neuropsychiatric complications.
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.
NON-DRUG POISONS
A vast array of plants, garden preparations, pesticides, household
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 poisons
and the reader is strongly advised to contact one of the poisons
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 depression
decisions regarding drug treatment involve a balance
between the efficacy of the drug and the risk of further overdose.
Selective serotonin reuptake inhibitors are safer alternatives
to tricyclics.
Key points
ACCIDENTAL POISONING
CRIMINAL POISONING 449
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.
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 childproof
containers and patient education should reduce the incidence
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 organophosphate
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 toxicological
screens are invaluable.