Although the use of cathartics and enemas is traditional, these measures are most unlikely to reduce absorption since this usually occurs rap­idly in the upper small intestine. They can only add to the misery and discomfort of the patient Efficacy in removal of drug has never been es­tablished. In one recent study, saline catharsis had no beneficial effect whatsoever on the ab­sorption of aspirin taken with charcoal (Sketris et al. 1982).

Whole Gut Lavage

One situation where attempts to empty the bowel may be helpful is in poisoning with ’slow’ or ‘timed release’ formulations. The number of such preparations on the market is increasing and since they usually contain a much larger dose of drug than ordinary tablets, intoxication may be severe and prolonged.

In such circumstances, rapid emptying of the bowel might limit in absorption. The preferred technique is ‘whole gut lavage’ in which normal saline is given by nasogastric tube at a rate of 2 litres an hour (Woo et al. 1976). Although this technique is readily controlled and rapidly effective in emptying the bowel in conscious patients being prepared for abdominal surgery, its efficacy in removing un-absorbed drug has yet to be established. It may not be effective and could possibly be dangerous in poisoned patients with grossly depressed gas­trointestinal motility.

Activated Charcoal

Activated charcoal has great adsorptive ca­pacity and can reduce the absorption of many compounds if taken orally at the same time (Neuvonen 1982; Pond 1986). The charcoal must be given in great excess (at least 10 times the weight of the drug) and efficacy falls off rap­idly as the time interval between ingestion of the poison and administration of the charcoal increases. After 1 hour, there is little inhibitory effect on the absorption of most drugs, although a significant reduction has been reported with phenytoin.

The time interval during which ac­tivated charcoal can significantly reduce ab­sorption following overdosage may be increased by the presence of food in the stomach (Olkkola & Neuvonen 1984). Oral activated charcoal ap­pears to be as effective as emesis induced by syrup of ipecac in limiting absorption (Neuvo­nen et al. 1983), but its administration after gas­tric lavage is of little or no benefit (Comstock et al. 1982).

Although the delay between inges­tion of the drug and arrival in hospital is usually such that significant reduction in absorption by oral activated charcoal is unlikely, there is no contraindication to its use and repeated admin­istration greatly increases the elimination of some drugs.

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Although unabsorbed drug in the stomach may be removed by gastric aspiration and lav­age its usefulness in practice has been seriously questioned (Proudfoot 1984). Most drugs and poisons seem to be absorbed rapidly and this technique is unlikely to be productive more than 4 hours after ingestion, unless gastric emptying has been delayed by opioid analgesics, anti­cholinergic agents, central nervous system de­pressants, and possibly salicylates. In such circumstances gastric lavage may be worthwhile up to 12 hours after ingestion.

It is said to be contraindicated after ingestion of corrosives and hydrocarbons such as paraffin because of the risks of perforation and lipoid pneumonia, respectively.

The patient must be correctly positioned head down in the left lateral position and a cuffed endotracheal tube inserted beforehand if the protective pharyngeal reflexes are depressed. It is essential to use a large bore tube (e.g. Jacques 30 gauge) and in adults lavage should be carried out with 300ml portions of warm tap water un­til the return is clear. Complications include pulmonary aspiration of stomach contents, and, rarely, oesophageal rupture.

Although gastric lavage is often unrewarding, large amounts of drug are occasionally re­covered. A common cause of failure is the use of too small a tube – an ordinary nasogastric tube is virtually useless. Large amounts of re­sidual drug have been found in the stomach postmortem after attempts at lavage with a nasogastric tube (Jenis et al. 1969), and in i case i large drug mass containing 25g of meproba­mate was removed by gastrotomy 40 hours after ingestion despite gastric lavage (Schwartz 1977).

Emetics

The comparative efficacy of induced emesis and gastric lavage is still debated. Neither guar­antees emptying of the stomach. Lavage is not always practicable in children because of the physical difficulty in passing a tube large enough to allow the passage of tablets, and emesis is probably preferable in young children. In 1 study in children poisoned with salicylates, emesis was claimed to be more effective than lavage (Boxer et al. 1969), but in another, only 10 to 15% of the amount of salicylate taken was recovered, even when emesis occurred within 1 hour of ingestion (Yaffe et al. 1970).

The major disadvantages are failure of eme­sis, particularly if central nervous system de­pressants have been taken, and toxicity, some­times fatal, from the retained emetic. Syrup of ipecac given with water is probably the best emetic, and is often effective within 15 to 30 minutes (Neuvonen et al. 1983).

Other agents which have been used include sodium chloride, copper sulphate, zinc sulphate, tartar emetic (antimony potassium tartrate), apomorphine and mustard. However, the over-enthusiastic use of sodium chloride and heavy metals can be ex­tremely dangerous and fatal poisoning with salt and copper sulphate has been reported (Gresham & Mashru 1982; Stein et al. 1976).

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