Activated charcoal (AC) is a highly effective, widely used adsorbent in clinical toxicology for the treatment of poisoning and drug overdose. It works by binding toxins in the gastrointestinal (GI) tract, preventing their systemic absorption.
Activated charcoal is an inert, tasteless, and odorless powder with a large surface area due to its porous nature. It is derived from organic materials like wood, coconut shells, or coal, processed at high temperatures to increase its adsorptive capacity.
Mechanism of Action
Activated charcoal exerts its detoxifying effect through adsorption, a process where molecules adhere to the surface of a solid rather than being absorbed into it.
Physical Adsorption: The porous surface of AC provides a large surface area (500–1500 m²/g) for binding toxic substances.
Van der Waals Forces: Weak attractive forces between charcoal and toxins help in trapping them.
Hydrophobic Interactions: Nonpolar toxins (e.g., benzodiazepines, phenobarbital) bind strongly to charcoal.
Ion Exchange: Some toxins, including weak acids and weak bases, can be bound by charge interactions.
Once toxins are adsorbed, they are excreted in feces without being absorbed into the bloodstream.
Indications: When is Activated Charcoal Used?
Activated charcoal is used in poisoning cases where the toxin is known to be adsorbable. It is effective in preventing the absorption of many drugs and chemicals.
Drug Overdose
Acetaminophen (Paracetamol) overdose
Salicylates (Aspirin poisoning)
Benzodiazepines (e.g., diazepam, alprazolam, lorazepam)
Barbiturates (e.g., phenobarbital, secobarbital)
Tricyclic antidepressants (e.g., amitriptyline, nortriptyline)
Opioids (e.g., morphine, codeine, tramadol)
Theophylline toxicity
Toxic Substance Ingestion
Pesticides and insecticides (e.g., organophosphates, carbamates)
Herbicides (e.g., paraquat, diquat) – effectiveness varies
Toxic alkaloids (e.g., strychnine, nicotine)
Cyanogenic glycosides (e.g., amygdalin from bitter almonds, cherry pits)
Gastrointestinal Decontamination
Activated charcoal is used to decontaminate the stomach and intestines after ingestion of toxic substances. It may be combined with a cathartic agent (such as sorbitol or magnesium citrate) to enhance elimination.
Contraindications: When Not to Use Activated Charcoal
Activated charcoal is not effective for certain poisons and should not be used in specific cases.
Poisons Not Adsorbed by Activated Charcoal
Corrosive substances (strong acids or alkalis such as sulfuric acid, hydrochloric acid, sodium hydroxide)
Heavy metals (iron, lead, mercury, arsenic)
Alcohols (ethanol, methanol, isopropanol, ethylene glycol)
Cyanide (does not bind effectively)
Lithium and potassium salts (e.g., lithium carbonate, potassium chloride)
Petroleum products (kerosene, gasoline) – high risk of aspiration
Medical Conditions Preventing Use of Activated Charcoal
Unconscious patients without a protected airway – High risk of aspiration into the lungs
Severe gastrointestinal motility disorders – Risk of charcoal bezoars (intestinal blockage)
Perforation of the gastrointestinal tract – Charcoal may cause complications
Dosage and Administration
The dosage of activated charcoal depends on the patient’s age, weight, and severity of poisoning.
Single-Dose Activated Charcoal (SDAC)
Used for acute poisoning, ideally within 1 hour of ingestion.
Adults: 25–100 g orally or via a nasogastric tube
Children (<12 years): 0.5–1 g/kg body weight (typically 10–25 g)
Multiple-Dose Activated Charcoal (MDAC)
Used for substances that undergo enterohepatic recirculation (drugs that re-enter the intestines after liver metabolism). It enhances elimination by intestinal dialysis.
Examples: Carbamazepine, theophylline, phenobarbital, dapsone
Dosage: 25–50 g every 4 hours (given for 24–48 hours)
Administration Methods
Oral Suspension: Mixed with water or juice to create a slurry
Nasogastric Tube (NGT): Used in unconscious or uncooperative patients
Side Effects and Complications
While generally safe, activated charcoal has some adverse effects:
Common Side Effects
Black stools (harmless but common)
Constipation or diarrhea
Nausea and vomiting
Serious Complications
Aspiration pneumonia – If charcoal enters the lungs, it can cause severe lung damage
Intestinal obstruction (charcoal bezoar) – Rare but occurs with multiple doses
Electrolyte imbalance – If given with sorbitol
Role of Activated Charcoal in Poisoning Management
Activated charcoal is often used alongside other treatments in poisoning cases:
| Step | Treatment |
| Step 1 | Airway, breathing, and circulation (ABCs) stabilization |
| Step 2 | Gastric decontamination with activated charcoal |
| Step 3 | Consider cathartics (e.g., sorbitol) for faster elimination |
| Step 4 | Administer specific antidotes if available (e.g., N-acetylcysteine for paracetamol) |
| Step 5 | Supportive care (hydration, oxygen, dialysis if needed) |
Alternative Treatments When Activated Charcoal is Ineffective
If activated charcoal cannot be used, other methods may be necessary:
Gastric lavage (stomach pumping) – Used in severe cases, within 30–60 minutes
Whole bowel irrigation – Used for iron, lithium, and sustained-release tablets
Hemodialysis – Used for methanol, ethylene glycol, and salicylates
Summary: Key Points About Activated Charcoal
Best used within 1 hour of toxin ingestion
Adsorbs many drugs and poisons, preventing systemic absorption
Not effective for alcohols, heavy metals, corrosives, or hydrocarbons
Dosage varies by age and poisoning severity
Multiple doses can enhance elimination of certain drugs
Complications include aspiration and intestinal obstruction
Conclusion
Activated charcoal remains an essential first-line antidote for many poisoning cases. Its effectiveness depends on timing, toxin type, and proper administration. However, careful patient assessment is necessary to avoid complications, and other decontamination methods should be considered when charcoal is ineffective.
