Activated charcoal (AC) is an excellent nonspecific adsorbent. The current debate regarding the role of AC in poison management relies on reconciling evidence-based studies in volunteers and heterogeneous poisoned and overdosed patients with clinical experience.4 AC should be considered for administration to a poisoned or overdosed patient after a risk-to-benefit assessment for the substance presumably ingested and ideally also for the circumstances of the exposure for a particular patient.13 The benefits include inactivating a potentially toxic xenobiotic; the risks include vomiting and subsequent aspiration pneumonia. The merits of AC as a decontamination strategy are discussed in detail in Chap. 7.
Activated charcoal, a fine, black, odorless powder, has been recognized for almost two centuries as an effective adsorbent of many substances. In 1930, the French pharmacist Touery demonstrated the powerful adsorbent qualities of AC by ingesting several lethal doses of strychnine mixed with AC in front of colleagues; he suffered no ill effects.6 An American physician, Holt, first used AC to save a patient from mercury bichloride poisoning in 1934.6 However, it was not until the 1940s that Anderson began to systematically investigate the adsorbency of AC and unquestionably demonstrated that AC is an excellent broad-spectrum gastrointestinal (GI) adsorbent.6-8
AC is produced in a two-step process, beginning with the pyrolysis of various carbonaceous materials such as wood, coconut, petroleum, or peat. This processing is followed by treatment at high temperatures with a variety of oxidizing (activating) agents such as steam or carbon dioxide to increase adsorptive capacity through formation of an internal maze of pores with a huge surface area.31,58,109,134 The rate of adsorption depends on external surface area, and the adsorptive capacity depends on the far larger internal surface area.31,102,108 The adsorptive capacity may be modified by altering the size of the pores. Current AC products have pore sizes that range from 10 to 1000 angstroms (Å), with most of the internal surface area created by 10- to 20-Å-sized pores.27,29,31 Most xenobiotics are of moderate molecular weight (100–800 daltons) and adsorb well to pores in the range of 10 to 20 Å. Mesoporous charcoals with a pore size of 20 to 200 Å have a greater capacity to adsorb larger xenobiotics as well as those in their larger hydrated forms.82
The relationship between AC surface area and adsorptive capacity was studied in vitro and in vivo in animals and in humans. When the surface area is large, the adsorptive capacity is increased, but affinity is decreased because van der Waals forces and hydrophobic forces are diminished.136 The actual adsorption of a xenobiotic by AC is believed to rely on hydrogen bonding, ion–ion, dipole, and van der Waals forces, suggesting that most xenobiotics are best adsorbed by AC in their dissolved, nonionized form.31 A superactivated charcoal with a surface area approximately double the current AC formulations demonstrated in both ...