Tuesday, November 20, 2012

Charcoal: Reserved For Grilling?

The Gist:  Use of activated charcoal (AC) for toxic ingestion is controversial and has been a polarizing topic at times, but most people agree that its utility is limited and should be individual and situation dependent.  The research and evidence base in toxicology is different than much of medicine due to the variable, unpredictable nature of exposures and the reporting bias of these cases.  Weigh the benefits (toxicity of the substance, time of ingestion..the sooner the better, availability of an antidote) with the risks (mentation, airway status) in each situation.  If in doubt, ask a toxicologist/call the poison center.

I just completed a toxicology rotation and sometimes it felt like I was cheating as a result of my prior interactions with toxicology via FOAM.  A bread and butter topic that arose frequently at the poison center and hospital was the use of activated charcoal and many practitioners calling in weren't sure of the role of charcoal.  I realized I, too, needed a review on the topic.  I found good reviews in the Freeemergencytalks.net talk 'Is Charcoal Obsolete?' and a debate, "Activated Charcoal is Obsolete" and the excellent toxicologists and reading filled in the rest.  The AACT position statement on activated charcoal summarizes the data on specific drug recommendations and continues to recommend individual consideration of whether charcoal would benefit a patient when given within an hour of ingestion.

Review of AC 
Predominantly from Goldfrank's Toxicologic Emergencies 
 "Antidotes in Depth - Activated Charcoal" by Hammond
Composition - the process generates an absorptive material due to massive surface area
  • Carbonaceous materials heated to decomposition and treated with oxidizing agents at high temperatures to create pores.  
    • Size of these pores dictates the surface area of the material (which affects toxin adsorption)
Adsorption - binding of the xenobiotic to the charcoal.  This may reduce blood levels of drugs between 24-47%, depending on the time frame of administration but does not necessarily translate into a clinically significant outcome.
  • Various forces at play.  Typically adsorbed in dissolved, non-ionized form
  • Adsorptive capacity directly related to surface area (higher surface area = greater adsorptive capacity)
  • pH dependent
    • Weak bases adsorbed better at higher pH, weak acids at lower pH
  • May desorb
    • pH dependent process (weak acids may desorb from AC as the complex passes from the acidic stomach to the small intestine, freeing up toxins later)
Adverse effects
  • Aspiration - incidence has varied from 4-25%, some association with altered mental status.  
    • Debatable about how much this matters.  Some claim that we all aspirate but charcoal is the “bad guy” because it’s very clearly noticeable in the endotracheal tube but may not be clinically relevant. For example, this article by Moll et al demonstrates a low incidence of new infiltrate after AC administration.  There are reported cases of long term sequelae from charcoal aspiration such as this one in Pediatrics, but in this case the problem actual resulted from accidental placement of the nasogastric tube into the trachea (thus directly filling the lungs with charcoal).
  • Peritonitis (if perforated GI tract)
  • GI:  Emesis, Constipation, Diarrhea
  • Corneal abrasions 
Administration - recommendations are on an individual basis with attention to risk versus benefit
  • In favor of administration
    • Xenobiotic available for adsorption in the GI tract
      • Early presentation after ingestion
    • Substance is toxic (removal from system very beneficial to patient) and no antidote available
  • Opposing administration
    • Tenuous airway status/high aspiration risk
    • Suspected or known GI perforation or need for endoscopy (caustic ingestions)
    • Abnormal GI exam, impaired motility
  • Co-therapies
    • Not recommended in conjunction with whole bowel irrigation or cathartics
  • Not very palatable
    • Tip from PharmD at the poison center - administer in chocolate syrup
Home and Prehospital
  • Studies demonstrate variable success in administration and airway/mental status is a concern.  According to a 2007 report in the Journal of Medical Toxicology, prehospital administration is often not in accordance with the AACT position statement (ie charcoal was administered at greater than one hour after ingestion). This paper did not delve into clinical significance of these deviations.  Also, many efforts in toxicology are "last ditch" efforts due to the often severe, novel nature of these exposures.
Dosing
  • 1 g/kg of body weight
  • Attempt at a 10:1 ratio of AC to xenobiotic to tie up the toxin
  • Usually ~ 50-100 g in an adult (10-25 g in children <1 year old, 25-50 in children 1-10 years old)
Multiple-dose AC (MDAC) - Mostly out of favor.
  • Consider In:
    • Delayed/prolonged release (bezoars, enteric coating, extended release formulations)
    • Prevent reabsorption (activated metabolites/xenobiotics)
    • Drugs that undergo enterohepatic circulation (dapsone, quinine, theophylline). 
    • Drugs with toxicokinetics similar to hemodialysis: low volume of distribution, low protein binding.
  • Dosing - depends on the individual and the specifics of the ingestion
    • Load with standard dose of AC
    • Repeat at 0.25-0.5 g/kg body weight every 1-6 hours.

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