Activated charcoal (AC) is used in emergency medicine to prevent the absorption of of potentially toxic substances from the gastrointestinal tract. AC is produced by steaming ordinary charcoal at high temperatures until it expands and forms a network of pores with a huge surface area relative to the volume of each charcoal particle. The basic idea is that AC sequesters drugs and other toxins within its pores; the AC and any toxins bound to it are then disposed of harmlessly in the patient's feces.
AC is diluted with sterile water and has the appearance of ink. Conscious patients can sip the mixture through a straw. AC can also be deposited in the stomach through a nasogastric tube; this technique is mainly reserved for unconscious or sedated patients.
AC has become the preferred method of gastric decontamination because it is not absorbed systemically and seldom induces vomiting. In contrast, syrup of ipecac, which remained in vogue until the 1970's, works by inducing vomiting. Although vomiting may seem like a good way to rid the body of a toxic substance, there are two downsides. First, a person slipping into a coma may inhale the vomitus, resulting in a life threatening condition called aspiration pneumonia. Second, many studies comparing the efficacy of ipecac vs. AC showed that, in most cases, 30% or less of an ingested substance was expelled from the body after vomiting was induced. On the other hand, AC consistently prevented the systemic absorption of 60% or more of the same substance. Therefore, on average, AC is a 100% more effective treatment than syrup of ipecac.
As mentioned above, AC is used in cases of toxic ingestions involving drugs or household products. About half of the cases of drug ingestions reported to poison control occur in children, most of them under age 5. The remainder are adult patients who have who have accidentally or intentionally overdosed on over the counter or prescription drugs. AC is most effective if administered within one to two hours of a toxic ingestion. After two or more hours have elapsed, most of the toxin has probably been absorbed from the gastrointestinal tract.
Many, but not all, drug ingestions can be treated with AC. The major exceptions are metal poisonings such as iron pills and lithium. The reason is that once the metal salts dissolve, the metal ions are small enough to pass through the AC particles without binding to them. Iron overdoses are treated with whole bowel irrigation or the chelating agent desferoxamine. Lithium overdoses are usually treated by hemodialysis, in which the patient's blood is filtered through a machine similar to those used for kidney dialysis patients.