Toxicology

Musings On Charcoal

By Dr. Bram Dolcourt

Recently I’ve gotten a few “Huh?” thrown my way when I tell people that…

I am actively discouraging the routine use of charcoal for acute overdoses.

The teaching has generally been to give charcoal in the face of an overdose. To many, what I’m saying is a bit surprising. Believe it or not, the American Academy of Clinical Toxicology recommends against routine charcoal use. I thought I’d write a few musings about how and why we recommend using it when we do.

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The theory: Activated charcoal has a very high surface area. It will bind and hold a drug (xenobioic), preventing absorption. This will reduce the delivered dose to the patient and reduce toxicity.

Reality: There is very little evidence for the use of activated charcoal. It is occasionally useful and has potential for morbidity. Few patients who claim to have overdosed on a xenobiotic benefit from charcoal.

Who should get it?

For the undifferentiated intoxicated patient, charcoal should only be considered early in the ingestion. Generally, charcoal needs to make physical contact with the xenobiotic in order to absorb it. Once past the pylorus, the chance that charcoal will mix with the xenobiotic is fairly low. The stomach usually empties within 1 hour, although it may be as long as 2. Liquid preparations are absorbed too quickly for charcoal to have significant absorption.stomach

Some xenobiotics may reduce GI motility and prolong the useful window for charcoal. A few authors recommend giving charcoal up to 4 hours post-ingestion. While there is no specific evidence, what is clear is that to have a beneficial effect, charcoal needs to be given early in the ingestion for a non-liquid preparation, generally within 1-2 hours and certainly not beyond 4 hours.

That time frame is for the general case.  There are two other mechanisms of action that allow for alternate dosing for charcoal. First, some xenobiotics are reabsorbed and excreted into the bile (enterohepatic recirculation) or into the stomach (enterogastic recirculation). Charcoal can interrupt this recirculation and reduce the elimination half-life. Secondly, just as dialysis uses a membrane to separate substances from blood, the gut lumen can be used as a membrane to separate substances from blood. Amenable xenobiotics will cross from the blood, across the gut, into charcoal on the enteric side.

There is good evidence for using charcoal for 5 drugs: phenobarbital, carbamzepine, theophyllne, dapsone and qunine (quinidine). These are “Category A drugs.” For these xenobiotics the elimination half-life is reduced when charcoal is given.  Multiple doses of charcoal can further increase the elimination rate for these drugs.

Multidose charcoal works for other xenobiotics, although the evidence is not as good (these are not called Category B drugs, BTW). Phenytoin, glipizide, aspirin (in high concentration), valproic acid, cyclosporine, amitriptyline, and colchicine are all potentially amenable to multidose charcoal.

How much should I give?

Several authors recommend giving 1 g per kg of charcoal, orally. Following this recommendation means that a child who ingests grams of a potentially lethal xenobiotic will receive less charcoal than an adult who eats a few milligrams of something moderately toxic. When placed in that context, it becomes clear the appropriate dose of charcoal should be in relation to the amount of the xenobiotic ingested, with the gram per kilogram being a ceiling dose.

Realistically, you want a 10:1 ratio, gram per gram, of charcoal to xenobiotic for optimal absorption. More is not helpful. Many patients only need a few mouthfuls of charcoal, as opposed to 50 or 100 grams. Consider a digoxin overdose; even for a massive ingestion of 100 tablets, one would likely only need to give 1.25 g of charcaol, which translates to about 6 ml. For a similar ingestion of amlodipine, one would only need to give approximately 50 ml of charcoal, or about 1/5 of the standard dose. It is very clear that we are giving most patients far too much charcoal.

For multidose charcoal, the dosage is less clear. Typically we recommend ½ gram per kg, up to 25 grams, ever 4 hours. This recommendation goes against what I said above. This is probably more than is necessary, however as the indications for multidose charcoal are quite different, we can get away with it.

Why wouldn’t I give charcoal?

All people aspirate to some degree, every day. Usually this isn’t a big deal as it is a small amount. However, in the face an altered mental status or vomiting, people aspirate more. A nasogastric tube also may worsen the risk, as the lower esophageal sphincter is held open. An endotracheal tube may reduce, but does not eliminate, aspiration. The sepsis literature is quite clear that intubated patients still aspirate and I can certain attest to suctioning charcoal out of the ET of many intubated patients.

Charcoal is mostly benign, however it may cause a pneumonitis when aspirated. The additional of sorbitol may worsen the pneumonitis. Charcoal comes in a significant volume; 50 grams of charcoal is usually in 240 ml of total volume. Rapidly instilling this volume can trigger vomiting due to stomach distention. While you want the charcoal to go in as early as possible, rapidly squirting it down an NG tube, can be counter productive and result in respiratory compromise.

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A second and unusual complication may result from too much or two frequent multidose charcoal. In the setting of an ileus, multidose charcoal has resulted in charcoal bezoars. The charcoal was, effectively, compressed into briquettes, inside the gut lumen, resulting in obstruction.

The last complication comes from the sorbitol that is packaged with some charcoal. As there is little evidence for the benefits of using charcoal, there is even less for adding sorbitol (or any cathartic). The idea is that sorbitol increases transit time, removing the xenobiotic more quickly. Sorbitol also increases the total water content of the charcoal stool and may reduce the already small risk of a charcoal bezoar, but is of unproven benefit.

The issue comes about from inducing diarrhea and causing depletion in total body water and electrolytes. One of the ways a xenobiotic kills is by causing cardiovascular collapse. Inducing volume depletion, by osmotically drawing water into the gut, may worsen an already sick patient’s cardiovascular status. Electrolytes travel with water, resulting in an electolyte disturbance. Pediatric patient have developing severe metabolic disturbances from multiple doses of charcoal with sorbitol. Other decontamination strategies, such as urine alkalinization rely on a normal electrolyte profile, and charcoal with sorbitol may actually be counter-productive.

Tell me when I should use charcoal!

Like any drug, the astute clinician must weigh the risks and benefits of charcoal. First and foremost, a clinician needs to consider the lethality and potential morbidity associated with an overdose. Good supportive care has saved more lives than charcoal ever will. I may be so bold as to say that no one has every lived or died purely because of the prompt or lack of application of charcoal. What charcoal may do is moderate toxicity. For a non-lethal or unlikely to be lethal overdose, charcoal may not be needed. For a very lethal overdose, charcoal may reduce the toxicity so that very aggressive and attentive care could save the patient’s life.

Second, the clinician needs to examine the alternate therapies available. If there is a very good antidote or treatment available, charcoal is unlikely to add any benefits; the patient is going to fine either way.

Third, the clinician needs to consider how well the xenobiotic binds to charcoal. For any of the Category A drugs or the other listed medications, charcoal should be strongly considered as toxicity can be reasonably modulated. For metals, such as iron, or electrolytes, such as lithium, there is no potential benefit. For all others, the benefit is questionable.

Finally, patient factors need to be considered. A patient who is unconscious with a tenuous airway, there is a significant risk of charcoal aspiration; especially as an NG tube is needed. An aspiration and charcoal pneumonitis may be worse than the effects of the xenobiotic. Other patient factors to keep in mind: GI anatomy (bariatic surgery), age, co-operation (restraining and forcing down an NG tube on an agitated patient can be problematic), etc.

Can you give me some examples of what you would do?

Keep in mind that these are made up examples and may not encompass all issues, but here goes:

1)            A young patient presenting 1-hour post ingestion of 10-20 tablets of extra strength acetaminophen.

This patient is a possible candidate for activated charcoal. The patient is presenting early and doesn’t have any obvious contraindications.  This would be a 10 gram ingestion, thus using the 10:1 ratio, you would like to give 100 grams of charcoal, but probably can’t due to patient weight. The charcoal may prevent the patient from crossing the “possible toxicity” line on the Rumack-Matthew’s Nomogram, thus you may be able to prevent an admission. This ingestion is unlikely to be lethal and there is a very good antidote, so charcoal is probably not going to reduce morbidity or mortality.

2)            A young patient with a large ingestion of carbamazepine. The patient is sleepy.

I would give this patient charcoal at any point during the ingestion and I would repeat doses every 4 hours. Carbamazepine is a Category A drug and very amenable to charcoal. It is also cardiotoxic, with significant risk for lethality. On the minus side, carbamazepine decreases mental status. The patient’s airway will need to be watched, but this patient will likely benefit from multidose activated charcoal.

3)            A patient presents 1 hour after taking 10-20 risperidone tablets

This patient is not likely to benefit from charcoal and there is potential risk for harm. This is not likely to be lethal ingestion, and if it is, it will be from respiratory compromise or aspiration. Abnormal vitals and other derangements respond well to supportive care. Risperidone is a respiratory depressant, thus this patient may lose the airway with a full stomach, risking aspiration.

4)             A patient who was found down after binging on diazepam and alcohol.

Charcoal is probably not indicated for this patient. This patient is not presenting early and will likely get very little, if any, benefit from charcoal. The patient has a decreased mental status with significant risk of vomiting and aspiration. As long as the patient is breathing, and the airway protected, s/he is at little risk of morbidity or mortality. Endotracheal intubation would likely be the optimal strategy for a patient presenting like this, who needs intervention.

Final thoughts…

Charcoal can be beneficial, but is not the end all treatment for the intoxicated patient. It should be given, not as a reflex, but after careful thought, articulating the expected benefit. The dose should be 10:1 ratio of charcoal to xenobiotic. Charcoal should be avoided when the ingested xenobiotic is not expected to cause morbidity or mortality after other care. The risk/benefit ratio of charcoal needs to be assessed in the context of patients with factors that may predispose to aspiration.

Dr Bram Dolcourt is an Assistant Professor in the Department of Emergency Medicine at Wayne State University in Detroit, MI.  He completed a fellowship in Toxicology in 2009

2 Responses

  1. Always good incite from a Bram. Thanks. Cheers!

  2. Good insight into the use of Activated Charcoal. A lot of clinicians do see charcoal as an antidote and will give it regardless of the ingestion and regardless of the time of ingestion. That’s why it’s important to contact your local Poison Information Center early. These folks have the training and experience to know when it’s likely to be of good benefit and when it’s not. These folks are the experts in the ever changing world of toxicology.
    Thanks again for a magnificent article!

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