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.