CLINICAL PHARMACOLOGY
Activated Charcoal
Activated charcoal is produced by pyrolysis of organic
material, such as wood, and an activation process which cleanses and fragments
the charcoal by exposure to an oxidizing gas compound of steam, oxygen, and
acids at high temperatures resulting in increased surface area through the
creation of numerous external and internal pores. These pores serve as
reservoirs to adsorb substances admixed with activated charcoal, making it a
useful adsorbent for specified toxins.
Activated charcoal is pharmacologically inert and is not
absorbed in the gastrointestinal tract. Activated charcoal will adsorb a
variety of organic and inorganic substances, but is especially effective in adsorbing
compounds within a molecular weight range of 100 to 1,000 Daltons (AMU's)1.
Several other physiologic and physicochemical factors influence the adsorptive
capacity of activated charcoal including: pH, charcoal: drug ratio, gastric
contents, and adsorption kinetics.2
Much of the published scientific literature which studied
the adsorptive capacity of activated charcoal was conducted using in vitro models.
A considerable amount of the research may be invalid since the effects of
physiologic pH were not taken into consideration or held constant. Using
research models which simulate the gastric environment, some toxins were not
adsorbed by activated charcoal. This data was inappropriately extended to imply
that activated charcoal did not adsorb a toxin and therefore had no efficacy in
the management of that type of poisoning incident. However, the research failed
to consider that the increased pH of the small intestine provides a receptive
environment for the adsorption of the toxin by activated charcoal. Activated
charcoal will effectively adsorb acidic, alkaline and neutral substances (not
to suggest use of activated charcoal in poisonings caused by corrosive agents2).
The extent of adsorption will be dependent upon the relative solubility of the
drug at a specified pH.
The optimal dosage ratio of activated charcoal to toxin
is described as 10:1. 3,4,17,18 Numerous factors contribute to and
interfere with adsorptive capacity, therefore, the 10:1 ratio may not be valid
in the clinical setting. Furthermore, a primary application of activated
charcoal is in adult patients who have intentionally ingested a toxin for drug
abuse or suicidal purposes. These patients may not freely provide information
about the substance or amount ingested, or have a decreased level of
consciousness. Under these conditions it is difficult to determine the
ingestion history, making it impractical to use the 10:1 ratio. The 10:1 ratio
is also impractical when large amounts of toxin have been ingested (i.e., an overdose
of 50 gm of aspirin would then require 500 gm [1.1 lbs.] of activated
charcoal).
Gastric contents may also compete with ingested toxins
and compromise the adsorption of the toxins by activated charcoal. 2
If activated charcoal is to be administered to a patient known to have ingested
a large meal in close proximity to the time of treatment, a larger dose of
activated charcoal may be appropriate.
Under appropriate physiologic conditions activated
charcoal adsorbs toxins instantaneously. This adsorptive process is reversible
and an equilibrium between free and bound toxin will exist. According to the
law of mass action the amount of free drug decreases as the dose of activated
charcoal increases. Â Therefore, large doses of activated charcoal can favor the
equilibrium toward greater toxin adsorption and efficacy. There is limited
evidence that desorption of a toxin from activated charcoal may occur.19
Therefore, there is a potential for toxin readsorption and enhanced toxicity.
The current standard of care is to administer a cathartic with single doses of
activated charcoal to hasten the elimination of the toxin/activated charcoal
complex from the gastrointestinal tract.5 Cathartics should be used
with extreme care during multiple dose activated charcoal therapy and it is not
recommended to use a cathartic with each dose of activated charcoal.5
Sorbitol
Sorbitol is a hexahydric sugar alcohol which primarily
serves as an osmotic cathartic in Actidose® with Sorbitol.6 A
secondary advantage of using sorbitol is as a palatability enhancer to decrease
the innate gritty texture of activated charcoal and to provide a sweet vehicle
to increase patient compliance. Sorbitol is poorly absorbed during its transit
through the gastrointestinal tract. Absorbed sorbitol is metabolized by the
liver and slowly converted to fructose. Insulin is not necessary for
intracellular transport of sorbitol, therefore customary cathartic doses can be
safely used by patients with diabetes mellitus.
As a hyperosmotic cathartic sorbitol produces a
hygroscopic action resulting in increased water in the large intestine and
increased intraluminal pressure which stimulates catharsis. Studies have been conducted
in healthy adult human volunteers using therapeutic amounts of activated
charcoal and sorbitol.8,9 Catharsis of activated charcoal occurred
in an average of 1.0 - 1.5 hours and persisted for 8 - 12 hours. Fourteen
poisoned patients are reported in one series representing a wide range of
toxins and dosages of sorbitol resulting in the onset of catharsis in an
average of 7.7 hours.10 The onset of action may be expected to be
longer in patients who have ingested toxins which decrease bowel motility, such
as pharmacological agents and plants with anticholinergic properties, and drugs
like narcotics.20
Sorbitol does not compromise the adsorptive capacity of
activated charcoal.11,12
REFERENCES
1. Activated Charcoal, Antidotal and Other Medicinal Us
es , Marcel Dekker, New York, 1980.
2. Clinical Pharmacokinetics . 1982; 7: 465-489.
3. Handbook of Common Pois onings in Children, American
Academy of Pediatrics, Evanston, 1983.
4. Am J Emerg Med. 1985; 3: 280-283.
5. Pois index Information Sys tem, Micromedix, Denver,
1991.
6. J Pediatrics . 1981; 98: 157-158.
8. Clinical Toxicology. 1985; 22: 529-536.
9. Ann. Emerg. Med. 1985; 14: 1152-1155.
10. Clinical Toxicology. 1985; 23: 579-587.
11. J. Pharmacol. Exp. Ther. 1982; 221: 656-663.
12. Am. J. Hos p. Pharm. 1978, 35: 1355-1359.
17. Medical Toxicology. New York, Elsevier, 1988.
18. Clinical Management of Pois oning and Drug Overdos e.
Philadelphia, W.B. Saunders Co., 1990.
19.Arch Intern Med. 1987; 147: 1390-1392.
20. ClinToxicol. 1989; 27: 91-99.