Activated charcoal: a spoonful of sugar

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 Alcohols 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. 1 Administration

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.