This is a common technique of enhancing elimination of drugs and has been demonstrated to increase the clearance of a substantial number of drugs in experimental situations. Demonstrable clinical efficacy, however, is restricted to only a very few drugs e.g. theophylline.

The use of repeated activated charcoal is likely to produce a meaningful clinical outcome for the following drugs

• Carbamazepine
• Clonidine
• Colchicine
• Dapsone
• Digitoxin
• Oral contraceptives!!!
• Phenobarbitone
• Phenytoin
• Quinidine
• Salicylate
• Tricyclic antidepressants
• Theophylline
• Verapamil
• Warfarin

Repeated doses of activated charcoal can increase the clearance of drugs by interrupting enterohepatic circulation. The other putative mechanism is by 'gastrointestinal dialysis'. Lipid soluble drugs of relatively low molecular weight are able to move from the gut capillaries back into the lumen (if there is a diffusion gradient) and be bound to charcoal (which maintains the gradient). The relative importance of these two mechanisms is largely unknown and of theoretical interest only.

A number of dosing strategies have been suggested:

• 25-50 g (0.5 g/kg) every 4 hours
• 25 g every 2 hours
• 10-15 g every hour
• or continuously down a nasogastric tube

There are little data to justify making a definite choice between these options. We would generally use 25 g every 2 hours as a compromise between practical considerations and the theoretical advantages of more frequent administration.

There are also little data to make firm recommendations on the time over which this strategy should be followed. A practical solution is to continue until there is a sustained improvement in the patient's clinical condition or until drug concentrations (if available) are below the concentration at which major complications are likely to occur. In all but the most serious cases this is usually less than 12 hours after treatment commences.

Position statement and practice guidelines on the use of multi-dose activated charcoal in the treatment of acute poisoning. American Academy of Clinical Toxicology; European Association of Poisons Centres and Clinical Toxicologists. J Toxicol Clin Toxicol 1999;37(6):731-51