A1: Antidotes in Depth

INTRODUCTION

Activated charcoal (AC) is an excellent nonspecific adsorbent. Understanding AC's role in poison management is established by the integration of pharmacologic data, controlled volunteer trials, studies in heterogeneous patients with overdose or poisoning, and clinical experience.²⁴ AC should be considered for a poisoned or overdosed patient after a risk-to-benefit assessment of the presumed ingested substance and patient-specific factors and circumstances.¹¹ Benefits include preventing absorption or enterohepatic recirculation of a potentially toxic xenobiotic; risks include vomiting and subsequent aspiration pneumonitis. A detailed discussion of the merits of AC as a decontamination strategy is presented in Chap. 8.

HISTORY

Activated charcoal, a fine, black, odorless powder, has been recognized for more than two centuries as an effective adsorbent of many substances. Organic chemist Scheele's first use of charcoal to absorb gases in 1773 was followed by Lowitz's use of charcoal with colored liquids in 1791.^6,84 In 1830, the French pharmacist Touery demonstrated AC's powerful adsorbent qualities by ingesting several lethal doses of strychnine mixed with AC in front of colleagues, suffering no ill effects.⁶ An American physician, Holt, first used AC to save a patient from mercury bichloride poisoning in 1834.^6,84 However, it was not until the 1940s that Andersen began to systematically investigate the adsorbency of AC and unquestionably demonstrate that AC is an excellent, broad-spectrum gastrointestinal (GI) adsorbent.^{6,7, and 8}

PHARMACOLOGY

Chemistry and Preparation

Activated charcoal 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 (600°–900°C) with a variety of oxidizing (activating) agents such as steam, carbon dioxide, or acids to increase adsorptive capacity through formation of an internal maze of pores.^26,56,112 Typical AC surface areas average 800 to 1200 m²/g.¹¹⁰

Mechanism of Action

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.²⁶

Pharmacokinetics

Activated charcoal is pharmacologically inert and unabsorbed. Its GI transit time is influenced by the type and quantity of an ingested xenobiotic, fasting and hydration status, muscarinic and opioid receptor xenobiotic properties, perfusion, and the use of associated cathartics or evacuants, among other factors. In six volunteers acting as their own controls, AC alone or administered with sodium chloride, sodium sulfate, magnesium sulfate, or a proprietary cathartic "salt" (36.7% anhydrous citric acid, 17.65% magnesium sulfate, and 45.6% sodium bicarbonate), the GI transit times to fecal evacuation were 29.3 ± 1.2 hours, 24.4 ± 1.2 hours, 15.4 ± 3.0 hours, ...