Patients who have ingested toxins in potentially harmful amounts may be considered for gastrointestinal decontamination if poisoning has been recent. Activated charcoal Given orally as a slurry, activated charcoal absorbs toxins in the bowel as a result of its large surface area. It can prevent absorption of an important proportion of the ingested dose of toxin, but efficacy decreases with time.

 Activated charcoal

 is most effective if given within 1 hour of overdose, but may have useful efficacy later than this, for example if a sustained-release preparation has been taken or when gastric emptying is delayed. Use is ineffective for some toxins that do not bind to activated charcoal (Box 1). In patients with impaired swallowing or a reduced level of consciousness, activated charcoal given via a nasogastric tube carries a risk of aspiration pneumonitis, but this can be reduced (though not eliminated) by protecting the airway using a cuffed endotracheal tube.

Box1. Substances poorly adsorbed by activated charcoal

Multiple doses of oral activated charcoal (50 g 6 times daily in an adult) may enhance the elimination of some substances at any time after poisoning (Box 2). This interrupts enterohepatic circulation or reduces the concentration of free drug in the gut lumen, to the extent that drug diffuses from the blood back into the bowel to be absorbed on to the charcoal (‘gastrointestinal dialysis’). A laxative is generally given with the charcoal to reduce the risk of constipation or intestinal obstruction by charcoal ‘briquette’ formation in the gut lumen.

 Evidence suggests that single or multiple doses of activated charcoal do not improve clinical outcomes after poisoning with pesticides or oleander.

Box2. Examples of poisons effectively eliminated by multiple doses of activated charcoal, haemodialysis or haemoperfusion

Gastric aspiration and lavage

 Gastric aspiration and/or lavage is very infrequently indicated in acute poisoning, as it is no more effective than activated charcoal for most sub stances and complications are common, especially pulmonary aspiration.

It is contraindicated if strong acids, alkalis or petroleum distillates have been ingested. Use may be justified for life-threatening overdoses of those substances that are not absorbed by activated charcoal (see Box 1).

Whole bowel irrigation

 This involves the administration of large quantities of osmotically balanced polyethylene glycol and electrolyte solution (1–2 L/hr for an adult), usually by a nasogastric tube, until the rectal effluent is clear. It is occasionally indicated to enhance the elimination of ingested packets of illicit drugs or slow-release tablets such as iron and lithium that are not absorbed by activated charcoal. Contraindications include inadequate airway protection, haemodynamic instability, gastrointestinal haemorrhage, obstruction or ileus. Whole bowel irrigation may precipitate nausea and vomiting, abdominal pain and electrolyte disturbances.