Activated Charcoal

Activated charcoal, the most commonly used adsorbent, is often called the universal antidote. The large surface area of the charcoal adsorbs the toxicant, thus reducing or preventing systemic absorption (Box 10-1). The quality of the various charcoal products depends on the size and surface area per gram of charcoal. On average, 1 g of activated charcoal has approximately 1000 square meters of surface area. Activated charcoal is produced by heating wood pulp to 900° C and, then washing it with inorganic acids and drying it. The resulting small charcoal particles are “activated” with steam or strong acids. The final adsorptive surface contains several carbon moieties that adsorb compounds with varying degrees of affinity. In vitro adsorption to activated charcoal in aqueous solutions is a nonspecific process that reaches equilibrium in less than 30 minutes. Once equilibrium is reached, some desorption can occur. For this reason, some individuals advocate using activated charcoal in conjunction with a cathartic, most commonly sorbitol, to speed gastrointestinal transit and thereby decrease the time available for desorption to occur.

Activated charcoal has an undisputed role in the treatment of acutely poisoned patients. The earlier it is administered after toxin ingestion, the more effective it is. Activated charcoal is particularly effective against large nonpolar compounds. Neutral molecules are more adsorptive than ionized toxins. Activated charcoal interferes with endoscopic visualization. In human volunteers an average of 62 hours elapsed after administration before stools were no longer black.21

The dosage of activated charcoal to be used varies with the individual product and other contributing factors, such as the amount of food present in the gastrointestinal tract. However, the dose-response curve indicates that higher doses are more effective. If the volume of toxicant is known, the general rule is to administer the activated charcoal in a dose of 10 times the dose of toxicant. Activated charcoal tablets and capsules are not as effective as activated charcoal slurries.22,23

For animals, the recommended dose of powdered activated charcoal and water is 2 to 5 g/kg of body weight (1 g activated charcoal in 5 mL water). If sorbitol is added as a cathartic, it is given at a dose of 3 mg/kg and mixed with the activated charcoal. If the intoxicant is subject to significant enterohepatic recirculation, repeat administration of activated charcoal every 4 to 6 hours for 2 to 3 days may be indicated. When multiple doses of activated charcoal are used, it is important that the patient be adequately hydrated to prevent constipation (kaolin-containing products can enhance the probability of causing constipation). Additionally, repeat dosing with sorbitol may cause significant hypotension or hypovolemic shock, particularly in small patients or those with underlying cardiovascular instability.

As mentioned, cathartic use in conjunction with activated charcoal has been advocated. Several cathartics have been used; however, sorbitol seems to have the fewest drawbacks and enhances the flavor of the suspension. Other cathartics used are sodium sulfate (Glauber’s salts) and magnesium sulfate (Epsom salts). Magnesium sulfate is not recommended in patients exhibiting CNS depression. Mineral oil should not be used in conjunction with activated charcoal because it coats the activated charcoal, blocking its ability to adsorb gastrointestinal toxicants.

Activated charcoal is contraindicated in patients with a compromised airway (without intubation), with hydrocarbon ingestion (because of an increased risk of aspiration), or with a gastrointestinal tract that is not anatomically intact. Activated charcoal should not be used in patients that have ingested caustic substances nor in those that are vomiting, having seizures, or are comatose unless endotracheal intubation has been accomplished to protect the compromised airway. The major complication of activated charcoal administration is emesis. Those patients receiving concurrent sorbitol cathartics are at higher risk of vomiting. In dogs administration of a sorbitol-containing solution in concentrations greater than 30% sorbitol frequently induces emesis.19

Care should be taken when using activated charcoal as it is very osmotically active and the potential exists to induce a clinically significant hypernatremia that might be difficult to control (more commonly seen in small breed animals, less than 30 lb). If possible a baseline sodium level should be obtained, and if the toxicant is known its ingredients should be reviewed. Hypernatremia can occur in patients with preexisting hypernatremia (e.g., dehydrated) or if the toxicant has excess sodium chloride (e.g., sodium bicarbonate, modeling clay, play dough) or osmotically active substances (e.g., gummy candies, sugar-free candies, sorbitol, paintballs, glycerol, bulk artificial sweeteners).