A fundamental challenge in estimating the magnitude of poisoning and drug overdose is delineating the types of conditions that should be included under this rubric. It is important to acknowledge that there is no standard definition of poisoning that is universally accepted and applied in clinical practice, in data collection, and in public health policy setting. Even within data collection systems, different definitions of eligibility for the purposes of case reporting may apply in various surveillance schemes (see Chapter 7).
In clinical terms, human poisoning subsumes any toxin-related injury. Such injury can be systemic or organ specific (e.g., neurological injury or hepatotoxicity). As important, the source of the toxin can be a synthetic chemical or a naturally occurring plant, animal, or mineral substance. Thus poisoning can include the toxic effects of a classic toxin (e.g., cyanide), an overdose of a prescription medication (e.g., an antidepressant), or an overdose of an over-the-counter preparation (e.g., headache tablets) or a complementary treatment (such as an herbal medicine or dietary supplement).
Although defining the foregoing events as poisoning is fairly straightforward, other classes of exposure may fall in or out of different classification schemes. “Envenomation” from a rattlesnake or a black widow spider clearly falls within the clinical context of poisoning and, therefore, is covered in depth in standard toxicological texts (Goldfrank et al., 2002; Olson et al., 2003). Envenomation may also overlap in some categorizations, however, with insect stings or “bites” that might not be considered toxic, but may be complicated by allergic responses, including fatal anaphylaxis.
A parallel set of issues is associated with medication responses that may not be dose related, but instead are idiosyncratic, with or without an allergic component. Clinical definitions of poisoning generally take into account unusual toxic responses that may involve susceptible subpopulations (e.g., toxic responses related to alternative metabolic pathways clinically relevant in only a subset of the population). Although this may overlap with the mechanisms of other types of poisoning, many definitional schemes separately tally or exclude altogether illnesses defined as adverse therapeutic events, such as drug toxicity that results from multi-drug interactions, increased susceptibility or true allergic sensitivity, or dosing error, all of which can be classified as “adverse drug effects.”
The toxic effects of ethanol present a specific set of definitional challenges. Acute ethanol toxicity in the context of frank overdose (e.g., rapid ingestion of a large amount of alcohol in a naïve drinker) can be lethal.