4 Nov 2019
Stephanie Phillips explains, with the help of TVM UK, how activated charcoal can be used to treat and range of poison cases.
Stephanie Phillips
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Image: Love the wind / Adobe Stock
The first reported use of activated charcoal (AC) was in 1811, and it has subsequently been widely used in the human and veterinary medicinal fields as a method of gastrointestinal decontamination.
AC is a carbon-based compound activated with gases at high temperatures, therefore removing previously adsorbed substances.
The activation process also reduces particle size, creating an exceptionally porous product with a vast surface area of 950m2/g to 2,000m2/g, capable of adsorbing organic compounds, such as drugs and toxins. Adsorption occurs by intermolecular forces (Van der Waals, or London dispersion forces), resulting in a bond with no chemical change to either the AC or the adsorbate.
A basic dose of 0.5g/kg to 4g/kg is advised (or 5ml/kg to 12ml/kg of liquid suspension), although some texts recommend the AC dose should exceed 10 times the ingested toxin.
AC can be administered in food for palatability, but studies have proven increased volumes of food will decrease the adsorptive efficacy of the AC. Consideration should also be given to enterohepatic recirculation, thereby necessitating repeated doses of oral AC with some toxins (such as theobromine and cannabis). Decreased efficacy of AC is directly associated with delayed administration.
Studies have been carried out in humans using AC to adsorb a range of drugs, assessing systemic absorption of the toxin. AC was administered at varied time intervals, with systemic toxin levels assessed depending on AC administration time. They found a mean reduction in absorption of 74% at 5 minutes and 16.5% at 120 minutes after ingestion of the toxin.
Many household items and foods exist that are toxic to dogs and cats, and are commonly ingested.
Some common poisons that are adsorbed by AC are:
Cathartic agents are recommended to improve gut transit time, and reduce the probability of release and reabsorption of the compound from the AC within the gastrointestinal tract. This can occur after just 30 minutes. Several types are available, such as bulking, osmotic and lubricant. Sorbitol is a saccharide osmotic cathartic, which is most commonly used.
Cathartics work by pulling water into the gut, increasing fluid volume – therefore stimulating gut transit. These should only be used for the initial dose, not for any repeated doses as this may exacerbate electrolyte derangements, specifically hypernatraemia. However, hypernatraemia has been reported in cases where no cathartic was used, due to the high osmotic activity of AC, therefore electrolytes and hydration status should be monitored regardless of cathartic use.
Sorbitol is recommended for use at 1ml/kg to 2ml/kg of the 70% solution.
Aspiration of AC carries a very poor prognosis, therefore careful consideration should be given to the appropriate route of administration. Reduced levels of consciousness may indicate administration by stomach tube. This should only ever be done with the patient intubated and the cuff inflated. AC should also be avoided if a suspicion exists of gastrointestinal perforation or ilius.
A 29kg Labrador retriever was reported to have eaten a 90g chocolate bar, with 70% cocoa. She was bright, but restless and tachycardic (140bpm), with a history of vomiting.
The lethal dose of theobromine is 250mg/kg to 500mg/kg, although 20mg/kg can cause symptoms such as tachycardia and diuresis.1,600 x percentage cocoa = theobromine in mg/100gThe patient was treated with emesis induction, fluid therapy and activated charcoal (AC) administered in a small amount of food. The AC doses were repeated at six-hour intervals for two days and her clinical signs resolved.
TVM UK offers a guide for calculating the dose of theobromine ingested, following the formula:
1,600 x percentage cocoa = theobromine in mg/100g
1,600 x 0.7 = 1,120mg/100g
90g bar = 1,120mg/100g x 90g = 1,008mg
1,008mg/29kg = 35mg/kg
The patient was treated with emesis induction, fluid therapy and activated charcoal (AC) administered in a small amount of food. The AC doses were repeated at six-hour intervals for two days and her clinical signs resolved.
