Haemodialysis, peritoneal dialysis, haemoperfusion, exchange transfusion and forced diuresis have all been used in attempts to increase the rate of removal of drugs and poisons. However, the amount of active drug removed is often disappointingly small, and the indications for the use of such measures is very limited.
Medical Services
Nevertheless, poisoned patients are often unnecessarily subjected to these potentially harmful measures, and the literature is full of anecdotal accounts of miraculous recovery attributed to such treatment (Winchester et al. 1977). Properly controlled clinical trials are difficult to carry out, and very few have been published. With the possible exception of forced alkaline diuresis for poisoning with salicylate and long acting barbiturates such as phenobarbitone, none of these methods for enhancement of drug removal has ever been shown to reduce morbidity or mortality in poisoned patients (Todd 1984).
Indeed, some studies suggest the opposite result. This is not to say that such measures are never necessary, or indeed sometimes life saving, but a more critical appraisal of their role is required.
In some cases, the drug presumed to have been taken has never been chemically identified, while, in others, haemodialysis has been carried out in patients with less than therapeutic plasma concentrations of the drug in question. Other studies have shown removal of only a very small and insignificant fraction of the ingested dose, sometimes amounting to the equivalent of less than 1 tablet or capsule (see, for example, Comstock et al. 1983; Heath et al. 1983). A misleading impression of efficacy may be gained by the use of nonspecific analytical methods for drug assay (Prescott 1974).
Other Binding Agents
Other agents have been used in attempts to bind unabsorbed drug in the gastrointestinal tract. Paraquat, a lethal weedkiller for which there is no known antidote, binds very strongly to Fuller’s earth and bentonite, and these adsorbents are used routinely in the treatment of paraquat poisoning.
Although bentonite may reduce the normally slow absorption of paraquat in pure aqueous solution in rats (Smith et al. 1974), ail the evidence points to extremely rapid absorption of paraquat from commercial weedkillers in man. Our experience of paraquat poi poisoning has been disastrous, with no apparent benefit from the early use of bentonite.
Cholestyramine binds acidic drugs and can reduce the absorption of paracetamol (acetaminophen) taken at the same time. Like activated charcoal, however, it is virtually useless when the delay between ingestion and administration exceeds 1 hour (Dordoni et al. 1973).
