A Textbook of Clinical Pharmacology and Therapeutics

INTENTIONALSELF-POISONING 445

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 effec-
tive antidote (acetylcysteine) is available, it is recommended
that the paracetamolconcentration 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 screen-
ing 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 man-
agement of poisoning.
Gastric aspiration and lavage should only be performed if
the patient presents within one hour of ingestion of a poten-
tially 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

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 char-

coal are required, typically ten times the amount of poison

ingested, and again timing is critical, with maximum effec-

tiveness being obtained soon after ingestion. Its effectiveness

is due to its large surface area (1000 m^2 /g). Binding of char-

coal to the drug is by non-specific adsorption. Aspiration is a

potential risk in a patient who subsequently loses conscious-

ness 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 pro-

longed elimination half-life (e.g. salicylates, quinine,dap-

sone, 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 sol-

vents are not adsorbed by activated charcoal.

Whole bowel irrigation using non-absorbable polyethylene

glycol solution may be useful when large amounts of sus-

tained-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

Table 54.2:Common indications for emergency measurement of drug con-
centration.

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

Table 54.3:Gastric aspiration and lavage

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