The adsorptive capacity of charcoal has been documented since the time of Hippocrates and has been known for centuries. Two independent researchers were responsible for its wide acceptance in the early nineteenth century when each of them performed a demonstration of its effectiveness by ingesting lethal doses of strychnine and arsenic, respectively, followed by charcoal. Both of them survived. The twentieth century has seen charcoal come into wide medical use as further investigation showed its effectiveness at adsorbing a wide variety of compounds.1 Activated charcoal is currently the most commonly used mode of decontamination in the Emergency Department for poisoned patients.2
Charcoal is produced by the distillation of the pyrolysis products of vegetable matter or wood. It works by directly adsorbing toxicants via a variety of chemical binding properties, and thus preventing substances in the gastrointestinal tract from being absorbed into the circulation. Enhancement of the adsorptive capability of charcoal is achieved by heating it to a temperature of 900°C and then subjecting it to a stream of oxidizing gas such as carbon dioxide gas or steam. This process is termed “activation” and creates an internal pore structure, which increases the surface area from 2 to 4 square meters per gram to greater than 2000 square meters per gram.2 A typical dose of 50 g of activated charcoal has the surface area of 10 football fields. Charcoal is not absorbed from the intestinal lumen nor is it modified by the numerous enzymes that aid in the digestion of food. It passes through the intestinal tract unchanged and is expelled as a sticky black substance.
Some charcoal preparations contain sorbitol. Sorbitol is typically used as a flavoring agent to make food, drinks, and medications more palatable. It is also used as a hyperosmotic laxative agent. It is poorly absorbed from the gastrointestinal tract and converted into fructose by the liver. Its limited absorption results in an increased volume of water being secreted into the intestine causing an increased intraluminal pressure that stimulates a catharsis.
Charcoal can help enhance the elimination of certain compounds by disrupting the enteroenteric or enterohepatic circulation. A diffusion gradient is created in the intestine due to the enormous adsorptive ability of charcoal to bind free toxicants. The intestinal mucosa essentially functions as a semipermeable membrane allowing absorbed drug or toxin to diffuse from the capillaries back into the lumen of the intestine. Charcoal can adsorb and “trap” it within the intestinal lumen to be subsequently eliminated.3,4 This mechanism essentially dialyzes the blood in the capillaries of the intestinal circulation, hence the term “gastrointestinal dialysis.” Similarly, drugs and drug metabolites secreted into the bile may be absorbed and trapped by charcoal within the intestinal lumen. By adsorbing these substances, activated charcoal may shorten the half-life, although evidence for clinical benefit of doing so remains limited. Substances that may benefit from multiple dosing of charcoal for enhanced elimination include phenobarbital, ...