A Textbook of Clinical Pharmacology and Therapeutics

Table 54.2: Common indications for emergency measurement of drug concentration.
Suspected overdose Effect on management
Paracetamol Administration of antidotes –
acetylcysteine or methionine
Iron Administration of antidote –
desferrioxamine
Methanol/ethylene glycol Administration of antidote –
ethanol or fomepizole with or
without dialysis
Lithium Dialysis
Salicylates Simple rehydration or alkaline
diuresis or dialysis
Theophylline Necessity for intensive care unit
(ITU) admission
urea, creatinine, oxygen saturation and arterial blood gases.
Drug screens are often requested, although they are rarely
indicated as an emergency.
Table 54.2 lists those drugs where the clinical state of a
patient may be unhelpful in determining the severity of the
overdose in the acute stages. In these, emergency measurement
of the plasma concentration can lead to life-saving treatment.
For example, in the early stages, patients with paracetamol
overdoses are often asymptomatic, and although it only rarely
causes coma acutely, patients may have combined paracetamol
with alcohol, a hypnosedative or an opioid. As such, an effective
antidote (acetylcysteine) is available, it is recommended
that the paracetamol concentration should be measured in all
unconscious patients who present as cases of drug overdose.
When there is doubt about the diagnosis, especially in
coma, samples of blood, urine and (when available) gastric
aspirate should be collected. Subsequent toxicological screening
may be necessary if the cause of the coma does not become
apparent or recovery does not occur. Avoidable morbidity is
more commonly due to a missed diagnosis, such as head
injury, than to failure to diagnose drug-induced coma.
PREVENTION OF FURTHER ABSORPTION
Syrup of ipecacuanha is no longer recommended in the management
of poisoning.
Gastric aspiration and lavage should only be performed if
the patient presents within one hour of ingestion of a potentially
fatal overdose. If there is any suppression of the gag
reflex, a cuffed endotracheal tube is mandatory. Gastric lavage
is unpleasant and is potentially hazardous. It should only be
performed by experienced personnel with efficient suction
apparatus close at hand (see Table 54.3).
If the patient is uncooperative and refuses to give consent,
this procedure cannot be performed. Gastric lavage is usually
contraindicated following ingestion of corrosives and acids,
due to the risk of oesophageal perforation and following
Table 54.3: Gastric aspiration and lavage
INTENTIONAL SELF-POISONING 445
1. If the patient is unconscious, protect airway with cuffed
endotracheal tube. If semiconscious with effective gag reflex,
place the patient in the head-down, left-lateral position. An
anaesthetist with effective suction must be present
2. Place the patient’s head over the end/side of the bed, so that
their mouth is below their larynx
3. Use a wide-bore lubricated orogastric tube
4. Confirm that the tube is in the stomach (not the trachea) by
auscultation of blowing air into the stomach; save the first
sample of aspirate for possible future toxicological analysis
(and possible direct identification of tablets/capsules)
5. Use 300 –600 mL of tap water for each wash and repeat three
to four times. Continue if ingested tablets/capsules are still
present in the final aspirate
6. Unless an oral antidote is to be administered, leave 50 g of
activated charcoal in the stomach
ingestion of hydrocarbons, such as white spirit and petrol, due
to the risk of aspiration pneumonia.
An increasingly popular method of reducing drug/toxin
absorption is by means of oral activated charcoal, which
adsorbs drug in the gut. To be effective, large amounts of charcoal
are required, typically ten times the amount of poison
ingested, and again timing is critical, with maximum effectiveness
being obtained soon after ingestion. Its effectiveness
is due to its large surface area (�1000 m 2 /g). Binding of charcoal
to the drug is by non-specific adsorption. Aspiration is a
potential risk in a patient who subsequently loses consciousness
or fits and vomits. Oral charcoal may also inactivate any
oral antidote (e.g. methionine).
The use of repeated doses of activated charcoal may be
indicated after ingestion of sustained-release medications or
drugs with a relatively small volume of distribution, and prolonged
elimination half-life (e.g. salicylates, quinine, dapsone,
carbamazepine, barbiturates or theophylline). The
rationale is that these drugs will diffuse passively from
the bloodstream if charcoal is present in sufficient amounts in
the gut or to trap drug that has been eliminated in bile from
being re-absorbed (see below). Metal salts, alcohols and solvents
are not adsorbed by activated charcoal.
Whole bowel irrigation using non-absorbable polyethylene
glycol solution may be useful when large amounts of sustained-release
preparations, iron or lithium tablets or packets
of smuggled narcotics have been taken. Paralytic ileus is a
contraindication.
SUPPORTIVE THERAPY
Patients are generally managed with intensive supportive
therapy whilst the drug is eliminated naturally by the body.
After an initial assessment of vital signs and instigation of