Activated charcoal uses in accidental poisoning

I will be using materials from StatPearls to throw more light on poisoning (Silberman et al. Activated Charcoal. 26 April 2023. https://www.ncbi.nlm.nih).

An oral suspension of activated charcoal (AC) is considered in poisonings when there is an indication for gastrointestinal decontamination of an ingested toxin, and where the activated charcoal can be administered within an hour of ingestion taking note of contra-indications.

Activated charcoal has been shown to significantly reduce the absorption of many ingested toxins when given within the first hour post-ingestion. Single-dose activated charcoal (SDAC) is given to significantly reduce drug absorption and bioavailability in the following circumstances:

• In anticipation of serious toxicity
• When the toxin ingestion occurs within 1 hour of administration, the decrease in absorption of the ingested toxin after 1 hour post-ingestion is unlikely to have clinical efficacy.
• Activated charcoal administration may be beneficial if administered up to four hours after large ingestions, ingestions of delayed-release drugs and ingesting substances with anticholinergic or opioid properties that decrease intestinal motility. 
• In alert and cooperative patients
• When airway reflexes are intact, or there is airway protection by an endotracheal tube
• Ingestions of toxins without specific antidotes
• The ingested toxin is known to be adsorbed by charcoal.  

Multiple-dose activated charcoal (MDAC) is often a consideration in cases of life-threatening ingestions of carbamazepine, dapsone, phenobarbital, quinine and theophylline. 

Mechanism of action

Activated charcoal adsorbs ingested toxins within the gastrointestinal tract preventing the systemic absorption of that toxin. Activated charcoal only absorbs toxins that are in the dissolved liquid phase via direct contact.

Orally administered activated charcoal does not get absorbed through the gastrointestinal lumen and acts within the gastrointestinal (GI) tract in its unchanged form. Ingested toxins come in contact with activated charcoal if the drug has not yet been absorbed from the gastrointestinal lumen or via recirculation of the toxin into the gut lumen by either enterohepatic recirculation, or entero-enteric recirculation through active secretion, or passive diffusion.

Activated charcoal adsorption of toxins is based on the equilibrium between the free toxin and the activated charcoal/toxin complex. Desorption of the toxin from activated charcoal may occur.

However, in the presence of adequate doses of activated charcoal, the equilibrium is shifted towards the activated charcoal/toxin complex. This attempt to shift the equilibrium in favour of activated charcoal/toxin complexes is the rationale for dosing activated charcoal to activated charcoal: toxin ratio of 10 to 1.

So a two-year-old boy weighing for instance 12kg, who has drank about 60ml of Paracetamol, each 5ml has 120mg of Paracetamol, and therefore the total taken by the boy will be 1440mg (1.44g). If the mother gave 15g of a slurry of Activated Charcoal mixed with water, it is within limits.

The optimal dosing for children (one month to 12 years) is 15mg per kg, which can be given every four to six hours as required with no more than four doses in 24 hours.

Activated charcoal best adsorbs toxins in their nonionised forms. Polar, water-soluble molecules are less likely to be adsorbed. Due to the pharmacodynamics of activated charcoal, it best absorbs nonpolar, poorly water-soluble organic toxins. 

Most ingested toxins will have decreased systemic absorption in the presence of activated charcoal, including acetaminophen (paracetamol), aspirin, barbiturates, tricyclic antidepressants, theophylline, phenytoin, and a majority of inorganic and organic materials.

It is important to note that activated charcoal does not effectively adsorb alcohols, metals such as iron and lithium, electrolytes such as magnesium, potassium, or sodium, and acids or alkalis due to the polarity of these substances.

Administration

Activated charcoal is given when it is certain that the ingested toxin is still in the gastrointestinal tract and when the benefits of preventing the absorption of the toxin are assumed to outweigh the risks posed by administering activated charcoal.

Activated charcoal administration can be oral or via nasogastric and orogastric tubes. When the dose of the ingested toxin is known, it is recommended that activated charcoal is given at a 10 to 1 ratio to the ingested toxin.

This ratio may be impractical when the patient has ingested large doses of a toxin. When the amount of toxin ingested is unknown, or it is impractical to achieve a 10-to-one ratio in large-dose toxic ingestions, SDAC should be administered at a dose of 1 g/kg of body weight or using a simplified age-based dosing scheme:

• SDAC dosing adult: 50 to 100 g
• SDAC dosing infants younger than one year: 10 to 25 g
• SDAC children two to 12 years: 25 to 50 g
• SDAC children older than 12 years: follow adult dosing

Multiple doses

Multiple-dose activated charcoal (MDAC) refers to the administration of two or more sequential doses of activated charcoal for enhanced elimination of the ingested toxin. MDAC appears to prevent ongoing absorption of drugs remaining within the GI tract and enhance elimination via enterohepatic or entero-enteric recirculation.

This is useful in “potentially life-threatening” ingestions of medications such as carbamazepine, dapsone, phenobarbital, quinine and theophylline. The dosing strategies of MDAC vary.

The initial dosing is either a 10 to 1 ratio of activated charcoal to the toxin or 1 g/kg of body weight. Interval MDAC doses range from 0.25 to 0.5 g/kg of body weight every one to six hours in adults. Some cases have employed the continuous administration of activated charcoal through an NG tube.

A simplified MDAC approach for adult patients:

• A loading dose of 25 to 100 g
• Repeat doses of 10 to 25 g of activated charcoal every two to four hours

Adverse effects

Pulmonary aspiration and resulting aspiration pneumonitis are the most concerning risks of the administration of activated charcoal. Aspiration from emesis and misplaced nasogastric tubes for activated charcoal administration can lead to severe respiratory compromise and even death.

Therefore, an adequate airway assessment must occur before activated charcoal administration.  In patients with a depressed level of consciousness, providers must consider the risk-to-benefit ratio of intubation for airway protection and the therapeutic benefits of activated charcoal.

Emesis occurs more often with rapid administration of activated charcoal and the risk of emesis increases when the activated charcoal has sorbitol added. Patients should be monitored for mental status changes and continued airway protection if emesis occurs.

While emesis is a common adverse effect, more significant gastrointestinal complications such as bowel obstructions have been reported after the administration of activated charcoal.

Patients with pre-existing motility disorders, those receiving opioids or antimuscarinic drugs and those treated with MDAC might be at greater risk. The likelihood of a more significant gastrointestinal complication following SDAC therapy is low. 

Contraindications

A position statement from the American Academy of Clinical Toxicology (AACT) in 2005 lists the following as contraindications and relative contraindications for activated charcoal use:

• Patients with an unprotected airway ( a depressed level of consciousness) without endotracheal intubation
• If activated charcoal use is likely to increase the risk and severity of aspiration of a toxin (hydrocarbons with high aspiration potentials)
• When the threat of GI perforation or haemorrhage is high secondary to medical conditions or recent surgery
• When endoscopy is likely to be attempted as activated charcoal may obscure endoscopic visualisation
• In the presence of an intestinal obstruction
• When activated charcoal is known to not meaningfully adsorb the ingested toxin such as metals, acids, alkalis, electrolytes or alcohols

MDAC is relatively contraindicated if decreased peristalsis is likely to occur from the substance ingested (opioids or anticholinergics). If these patients receive MDAC, they should be monitored closely for the development of obstruction or potential aspiration.

Despite the usefulness of activated charcoal in some cases of accidental poisoning, it is very important to rush the person affected to the nearest healthcare facility. 

Chief Pharmacist, 
Cocoa Clinic.