Activated Charcoal

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What is activated charcoal and how is it meant to work?

Form of carbon processed and treated chemically to create a large number of small pores which increase available surface area for binding to other substances, i.e. microporosity increases adsorptive capacity.
Adsorbent, i.e. poison molecules adhere to its surface
Not absorption whereby the poison molecules would dissolve into and permeate the activated charcoal

Activated charcoal fed to animals that have ingested poisons; not absorbed or metabolised itself, instead binds to some/most of the poison still in the gastrointestinal tract
Charcoal-poison mixture then excreted in faeces
Gastrointestinal decontamination minimises systemic toxin absorption
Considered core part of management of small animal poisoning

Which poisons does activated charcoal adsorb well?

What sorts of substances does activated charcoal bind most avidly to?
From a clinical point of view, are there poisons for which we should be using it versus ones for which we shouldn’t?
Is there any evidence about the relative adsorbent capacity of activated charcoal for different small animal poisons?

Adsorptive capacity likely dependent on/influenced by poison-specific factors, e.g. size and polarity of molecules, degree of ionisation etc.

Bates N, Rawson-Harris P, Edwards N. Common questions in veterinary toxicology. J Sm Anim Pract 2015. 56:298-306:

“The binding of activated charcoal has not been tested against all (or even many) drugs and chemicals, but is known not to significantly adsorb a number of substances such as acids and alkalis, alcohols and glycols (ethylene glycol), metals (e.g. iron, lead), oils and petroleum distillates (e.g. white spirit) and detergents.”

However no references cited.

Use of activated charcoal generally not recommended for caustic or corrosive substances due to apparent lack of efficacy; however unable to find good quality evidence.

Should we be using activated charcoal at all?

Some debate!
  
[Human medicine] The American Academy of Clinical Toxicology (AACT) and the European Association of Poisons Centres and Clinical Toxicologists (EAPCCT) position paper:

"Single-dose activated charcoal should not be administered routinely in the management of poisoned patients...[as]... there is no evidence that administration of activated charcoal improves clinical outcome."

But…a lack of evidence of a beneficial effect on clinical outcome is not the same thing as evidence of a lack of beneficial effect on clinical outcome.

Veterinary patients?

“What you can know for sure – unless I failed to find them – is that there are no good quality prospective randomised controlled trials in clinical canine and feline patients evaluating the impact of activated charcoal on clinical outcome.” (Shailen Jasani)

Multiple variables to be studied, e.g.

  • Individual poisons
  • Different doses of the same poison
  • Whether or not emesis was induced
  • Time from exposure to administration of activated charcoal
  • Etc.

Risk/Cost-benefit assessment: general perception is low risk and cheap with potential for some/considerable/life-saving benefit.

Relative lack of antidotes and other treatment modalities (e.g. haemodialysis, plasma exchange) in veterinary versus human medicine

Contraindications and potential adverse effects

Not risk free albeit clinically significant adverse effects considered very uncommon/rare
Use common sense – e.g. do not administer orally to patients at increased risk of aspiration due to neurological compromise

Clinically significant acute hypernatraemia:

Most commonly cited mechanism is that activated charcoal draws water osmotically into the GI tract; this is then voided causing volume depletion.
Patients may have other co-existing causes of water loss plus reduced water intake
More likely with concurrent cathartic administration – but anecdotally reported with use of activated charcoal alone

Minimising the risk:

  • Ensure patient is adequately (re)hydrated beforehand
  • Tailor approach with respect to blood testing of hydration parameters and use of fluid therapy to individual patient based on risk assessment (e.g. very young or very old patients, existing vomiting, etc.)
  • Patients discharged on multidose activated charcoal following successful induction of emesis: advise clients to ensure free access to water and to contact clinic if any ongoing vomiting or clinical concern; liberal approach to administering antiemetic/antinausea agent before discharge.  
  • Avoid activated charcoal if ingested poison is known/suspected to be one that (potentially) causes hypernatraemia (e.g. homemade play dough); use cautiously for poisons which may induce diuresis (e.g. theobromine (chocolate)).

Pay attention to dose being dispensed:

  • Recommended dose range 0.5-8 g/kg depending on resource consulted
  • Less precise/more liberal empirical dosing may be acceptable for bigger and asymptomatic patients
  • Calculate and measure out doses in patients where there is clinical/hydration status concern; use low end doses and well-spaced dosing intervals for multidose therapy.

Avoid activated charcoal if possibility of gastrointestinal perforation, obstruction or ileus
Some debate about need to avoid if oral medications or antidotes needed
Avoid if gastrointestinal endoscopy or surgery is likely in the near future
Constipation may occur with multiple dose therapy

Timing of administration

Ideally administer as soon as possible after toxin ingestion; efficacy decreases the more time passes.
Many resources suggest not to administer activated charcoal if more than 2 hours have elapsed; this author typically suggests a longer more liberal time frame.
In reality likely to depend on multiple factors, e.g.

  • Rate of toxin absorption from gastrointestinal tract
  • Presence of food
  • Type of preparation e.g. delayed or sustained release?
  • Whether enterohepatic circulation occurs
  • Other factors influencing gastrointestinal motility and function

Paper mentioned in this episode:

Bates N, Rawson-Harris P, Edwards N. Common questions in veterinary toxicology. J Sm Anim Pract 2015. 56:298-306.

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