Article
Activated charcoal: a spoonful of sugar
- Andrew Dawson
- Aust Prescr 1997;20:14-6
- 1 January 1997
- DOI: 10.18773/austprescr.1997.008
Activated charcoal is the decontamination treatment of choice for most poisonings. The dose is 1 g/kg of body weight. In primary care, it should be mixed with water and given as a slurry. Sorbitol and chilling may improve its palatability. In hospital, the first dose may be given with sorbitol. For a small group of poisonings, repeated doses of activated charcoal are useful in reducing morbidity or the time spent in hospital. Patients with poisonings involving sustained release preparations or drugs which do not bind activated charcoal should be considered for whole bowel irrigation with polyethylene glycol.
Introduction
Self-poisoning
should be considered as a presenting symptom for an
underlying psychosocial disorder which requires
assessment and intervention. When the ingested
amount is sufficient to cause harm, the
self-poisoning can be termed an overdose for which
decontamination may be needed. In this context,
patients may need reassurance that the purpose of
decontamination is therapeutic rather than punitive.
If decontamination is indicated, the treatment of
choice is activated charcoal for the majority of
cases. Giving activated charcoal alone has been
shown to be as efficacious as or superior to induced
emesis or gastric lavage with or without activated
charcoal. There is no longer any place for
ipecacuanha. Activated charcoal is increasingly
being recommended as first-line treatment for
poisonings that occur in the home and should be the
most commonly used method of decontamination for
patients admitted to hospital.
Physical properties
Activated
charcoal is produced from burnt organic matter which
is cooked in a supra-oxygenated atmosphere. This
produces pores within each grain of charcoal. These
pores effectively increase the surface area of
charcoal to 1000 m2/g. Activated charcoal
binds most drugs that are commonly used in
poisonings. The binding utilises weak electrostatic
forces between the activated charcoal's carbon and
the side chains of carbon based molecules. Activated
charcoal does not bind well to non-carbon based
drugs, substances which are strongly ionised or
alcohols (Table 1).
The binding of drugs to
charcoal is a dynamic process with molecules
binding, releasing and rebinding to other sites.
This binding can be affected by changes in pH as the
drug-charcoal complex moves through the
gastrointestinal tract. Although optimal ratios of
charcoal to drug can be established in vitro,
these data are of little help in the treatment of
potentially poisoned patients. In practice, the dose
required for the clinical use of charcoal has to
account for other variables such as stomach
contents, other drugs and the decreased binding
effect due to alcohol. For this reason, the normal
empiric dose of activated charcoal is 1 g/kg of body
weight. In Australia, charcoal is normally dispensed
as a slurry in 50 g bags, the slurry being made with
either sorbitol or water.
Table 1 Substances for which charcoal
is ineffective ethanol ethylene glycol methanol Strong acids or alkalis dishwasher granules 'Metal drugs' gold lithium iron potassium mercury |
Indications for decontamination
Ingestions that could be associated with a
significant risk of toxicity should be considered
for gastrointestinal decontamination. In the absence
of previous experience with the ingested toxin,
advice can be sought from a Poisons Information
Centre (phone 131126). The centre can provide advice
on both immediate and ongoing management and, when
required, connect the treating practitioner to a
consultant toxicologist.
Administration (Fig. 1)
Patients
requiring decontamination who are unconscious or
likely to lose consciousness need to be intubated to
protect their airway. Activated charcoal can then be
given down an orogastric or nasogastric tube. My
preference is to use an orogastric tube and to
aspirate stomach contents before giving activated
charcoal. Comparative studies show that the routine
use of gastrointestinal lavage is rarely indicated.
Fig. 1Administration
|
Conscious patients in whom decontamination is indicated should be offered the option of taking the activated charcoal orally. This route is less traumatic for the patient (and the staff). There are a number of issues which need to be addressed in order to increase the likelihood of the patient drinking the activated charcoal. The important steps are as follows.
1. Make sure decontamination is indicated.
2. Briefly explain to the patient in general terms your concerns about the potential toxicity of the ingested substance and therefore the requirement for the patient to receive decontamination. Point out to the patient that the majority of patients are able to drink the charcoal in preference to receiving it down a nasogastric or orogastric tube.
3. Enter into a time-limited contract with the patient to drink the dose of activated charcoal within 20 minutes. You may proceed with decontamination when medically indicated in intoxicated or suicidal patients without their permission, as you have a duty of care to those patients.
4. When medically indicated gastrointestinal decontamination is refused, the patient should be anaesthetised, intubated and ventilated and then decontaminated. The alternative of forcing a nasogastric or orogastric tube is more traumatic and labour intensive.
The palatability of activated charcoal can be improved if it is chilled. Aesthetically, it may be easier for some patients to take if it is served in a covered container with a large straw or simply if the patients are asked to drink it with their eyes shut. There have been a variety of attempts to improve the palatability of charcoal using the addition of a number of foods or additives. In controlled trials, activated charcoal administered with sorbitol was more palatable than activated charcoal with water. Similar results have been found with a number of other foodstuffs and flavouring agents with variable reduction of the binding capacity of activated charcoal. In a recent study, the addition of gelatin to charcoal to form a charcoal jelly was shown not to alter the binding capacity of activated charcoal. As a result of these studies, the only currently recommended additives in Australia are sorbitol and water.
The administration of activated charcoal with sorbitol in certain situations decreases bowel transit time; however, the results in terms of increasing the efficacy of decontamination are variable. Sorbitol is a hyperosmolar solution which acts as an osmotic cathartic by causing a shift of fluid from the vascular space into the gut lumen. Clearly, such volume shifts can potentially exacerbate the clinical condition of haemodynamically unstable patients. For this reason, most patients who receive activated charcoal with sorbitol require significant volume loading. In adults, the volume loading required is in the order of 1-2 L of intravenous normal saline. The addition of sorbitol to activated charcoal probably increases morbidity associated with pulmonary aspirations because of osmotically induced non-cardiac pulmonary oedema. For these reasons, I believe that activated charcoal in the home or primary care situation should be used with water alone.
Repeat dose activated charcoal
Following the initial decontamination, you
should consider whether repeated doses of activated
charcoal are indicated. Repeated doses are effective
in increasing the elimination of many drugs, either
by interrupting enterohepatic circulation or by
direct dialysis of the drug from gut
microvasculature into the intestinal lumen. Although
the list of drugs is extensive, this manoeuvre is
clinically useful for a relatively small number of
drugs (Fig. 1).
The other indication for this technique is for those medications which may form concretions in the stomach or have significant amounts left in the stomach because of delayed emptying (mostly drugs with anticholinergic adverse effects such as phenothiazines and tricyclic antidepressants). In these situations, the absorption of the drug is prolonged.
The repeated doses of charcoal are generally 50 g every 4 hours or 10 g/hour. The smaller dose given every hour is often better tolerated by patients. When using this technique, the patient and staff need a clear explanation of the goals and purpose of the treatment. Antiemetics may be required to control nausea.
Complications of therapy
Aspiration of activated charcoal with or
without sorbitol is well documented in the
literature. Conscious patients who have taken CNS
depressant drugs, but have been given activated
charcoal, require careful observation as a
deteriorating level of consciousness may be an
indication for intubation.
Concretions of activated charcoal have been reported to cause bowel obstruction. This is a very rare complication.
Patients given activated charcoal with sorbitol will have a significant fluid shift and generally require intravenous fluids. Colicky abdominal pain and diarrhoea are common and generally resolve within 6 hours. The patient's stool may remain black for a number of days.
Any patient who has received activated charcoal should be advised that this may absorb other medications normally taken in therapy. The implications of this need to be discussed with their doctor. Where possible, medications required during the period of decontamination should be given parenterally or sublingually. Women taking oral contraceptives should be advised to use an alternative method of contraception until the beginning of the next menstrual cycle.
Whole bowel lavage
The
medications listed under 'metal drugs' in Table 1
are not adsorbed onto activated charcoal. For this
group, and poisonings involving sustained release
preparations, polyethylene glycol is considered the
treatment of choice. Unlike sorbitol, polyethylene
glycol is iso-osmolar and is not dependent on fluid
shifts across the intestine to produce diarrhoea.
Studies in volunteers have shown at least equivalent
efficacy between the use of activated charcoal and
polyethylene glycol for most drug models.
Polyethylene glycol had a higher acceptance rate and
less associated gastrointestinal symptoms. The
patient is given 15-25 mL/kg/hour of polyethylene
glycol either orally or by nasogastric tube. The
endpoint for treatment is a clear rectal effluent.
Emesis may need to be controlled by altering the
administration rate and/or giving antiemetics. The
average duration of treatment is 4 hours.
Conclusion
The preferred method
of gastrointestinal decontamination for the majority
of patients is activated charcoal. Activated
charcoal should be the primary decontamination
choice for both pre-hospital and hospital treatment.
Successful oral administration is dependent on both
patient and staff education and motivation. When
clinically indicated, patient consent for
decontamination is preferred, but is not a
prerequisite for treatment.
Buckley NA, Dawson AH, Reith DA. Controlled release drugs in overdose. Clinical considerations. Drug Saf 1995;12:73-84.
Shihata N, Bakalova M, Finnin B, Meagher D, Corallo C. The relative adsorption properties of charcoal gel in comparison to charcoal suspension [poster abstract]. The proceedings of the 22nd Federal Conference of the Society of Hospital Pharmacists of Australia. Aust J Pharmacy 1996;26:182.
Pond SM, Lewis-Driver DJ, Williams GM, Green AC, Stevenson NW. Gastric emptying in acute overdose: a prospective randomised controlled trial [see comments]. Med J Aust 1995;163:345-9. Comment in: Med J Aust 1995;163:340-1.
Department of Clinical Toxicology and Pharmacology, Newcastle Mater Hospital, Newcastle, N.S.W.