Use of Activated Charcoal in Toxicology
Of the past paper questions, Question 29 from the second paper of 2010 asked for the greatest amount detail about the appropriate use of activated charcoal, and Question 15.4 from the second paper of 2012 expects the candidates to identify a bowel obstruction caused by a charcoal bezoar. The broad topic of post-overdose decontamination is discussed in another chapter, and is the subject of Question 1b from the second paper of 2004 and Question 5 from the first paper of 2002.
Rationale for the use of activated charcoal
- Activated charcoal is the product of the pyrolysis (i.e. decomposition by heat and in the absence of oxygen ) of organic matter. It is "activated" by a series of processes, among them heating it in steam or CO2 at a temperature of 600 Cº, washing with organic acids and drying with hot air. The activation process produces a highly porous substance with a massive surface area, up to 2000m2/g (LITFL quotes 3000 m2/g)
- Once activated, charcoal can act as a broad-spectrum gastrointestinal adsorbent (Andersen, 1948)
- Its highest affinity is for compounds with a molecular weight of 100–1000 Da (Krenzelok, 2002)
- Many pharmacologically active substances fall within this range.
- Most lifethreatening overdoses are by ingestion.
- Many such overdoses may present early.
- Gastric emptying rate may be affected (slowed) by the toxin itself.
- Ergo, giving charcoal early may reduce the absorption of the drug.
Single-dose activated charcoal
- Time is the most important factor determining efficacy.
- If the poison is not in the stomach, single-dose activated charcoal will be useless.
- Otherwise, activated charcoal should probably be given soon after most significant ingestions:
- The frequency of serious complications is low
- The worst thing that would usually happen is that it simply does not work
- After a drug is absorbed, there are few effective techniques to enhance its elimination
- Efficacy is inversely related to the time elapsed after the ingestion. The longer you deliberate about the usefullness of charcoal, the more useless the charcoal becomes. Stop wasting time and just give it
- This pragmatic why-not-have-a-go approach was championed by Isbister and Kumar in their 2011 recommendation paper for Current Opinion in Critical Care.
- At least one RCT did not demonstrate any benefit (Eddleston, 2002)
- In fact, the ED stay was longer, and there was more vomiting.
- Several similar studies have confirmed a relative lack of benefit in unselected patients
- On this basis of this, the AACT/EAPCCT recommendation in 2004 was not to give single dose charcoal unless it is clearly within 1 hour of the overdose, and unless the drug is well known to adsorb onto charcoal. In short, they were against the random use of charcoal for the undifferentiated overdose.
- This recommendation cannot be generalised to the severely intoxicated ICU population, as the major risk from charcoal is aspiration, and if your airway is protected with a big tube, that risk is minimal.
Multiple doses of activated charcoal
The rationale for multiple-dose charcoal is slightly different. It's not a matter of "just give more of it for more effect".
- Many drugs are excreted via the bile, and undergo extensive enterohepatic recirculation.
- Multiple dose choarcoal ensures that the cycle of recirculation is interrupted (i.e. the excreted drug is bound by charcoal instead of beaing reabsorbed).
- In this manner, it is a method of enhanced elimination.
The following is a list of well-accepted indications for multiple dose activated charcoal (from Pierre Gaudrealt, 2005)
Substances for which activated charcoal is known to be ineffective
Drugs which are absorbed too rapidly
Drugs which do not adsorb on to charcoal
- Corrosive substances, eg. strong acids and alkalis,
Complications of charcoal administration
- Its gross. Patients complain. However, actual vomiting appears to be rare (Isbister et al, 2011)
- It may absorb usueful medications as well as the toxin.
- It may increase the risk of aspiration (but if it does, then not y much)
- Aspirated, it may be more harmful than sterile gastric contents (but if it is, then not by much). In their answer to Question 29 from the second paper of 2010, the college lists direct administration of charcoal into the lung as a valid concern.
- It may cause bowel obstruction; this is rare, and usually associated with multiple dose charcoal in patients who are poisoned with an agent which affects gut motility.
Contraindications to charcoal administration
- Uncooperation. The use of physical restraint and a nasogastric tube may be viewed as unethical and/or illegal.
- Poor airway protection. The semicomatose overdose patient should probably be intubated for this.