Clinical pharmacokinetics of oral activated charcoal in acute intoxications.

Abstract

Activated charcoal has the ability to adsorb a wide variety of substances onto its surface. This property can be applied in preventing the absorption of various drugs and toxins from the gastrointestinal tract and in some cases to increase their rate of elimination. In vitro, the extent of adsorption depends mainly on the relative amounts of the charcoal and the drug ingested, but the quality and formulation of the activated charcoal, as well as other factors such as the pH of the incubation medium also have an effect. Under optimum conditions the adsorption to charcoal is a rapid process but desorption from charcoal is possible due, for example, to competition by other substances or to changes in pH. In acute poisonings the most important determinants of the efficacy of activated charcoal are the delay in the administration and the amount of activated charcoal given. Activated charcoal should be given as a water suspension as soon as possible, preferably within 30 minutes of the ingestion of the toxic agent. However, in acute intoxications the absorption of drugs may be considerably delayed and thus charcoal may be effective when administered 24 hours after drug ingestion. At a constant charcoal-drug ratio, the adsorption capacity of charcoal increases with increasing doses because the competitive effect of gastrointestinal contents diminishes. Thus the amount of charcoal should be as high as feasible, i.e. about 50 to 100g in adults. This amount is able to adsorb lethal doses of many drugs. Significant desorption from charcoal and subsequent systemic absorption of a drug is possible if inadequate amounts of charcoal are used. The adsorption to charcoal is more complete in poisonings with potent drugs, i.e. where the charcoal-drug ratio is high (e.g. digitalis glycosides, tricyclic antidepressants, etc.). With some drugs the adsorption capacity may be exceeded, e.g. in aspirin poisonings, but even in these cases the charcoal may adsorb that fraction of the drug which is dissolved in the gastrointestinal fluids. In experimental studies, the efficacy of charcoal in preventing systemic absorption of many drugs has been of the same order or even better than that of emesis, but in certain poisonings the efficacy of charcoal is inadequate, e.g. in those caused by ethanol, methanol or iron salts. Charcoal is rather ineffective and may even be contraindicated in poisonings caused by caustic alkalis or acids. Charcoal is non-toxic but, if administered too rapidly, patients may vomit. Some drugs and toxic agents have a long elimination half-life and are excreted into the gastrointestinal tract and then reabsorbed. With such agents multiple oral doses of activated charcoal, e.g. 20g every 6 hours for 1 or 2 days, can accelerate their elimination and shorten the duration of intoxication. There are considerable differences between various countries in the availability of activated charcoal and even between various medical centres in their willingness to use charcoal. Activated charcoal should be a part of the first-aid kit both at home and at work to avoid unnecessary delays in administration.