17.1: Drug Toxicity: Overview

Drug toxicity quantifies the harm a compound causes to an organism, varying by dose and potentially impacting whole systems or specific organs like the liver. Toxic reactions may arise from venomous insect or spider bites, with effects ranging from mild symptoms to severe outcomes such as brain damage or death. Common forms of acute poisoning include ethanol intoxication and overdose of pain or fever medications, with substances like GHB and heroin being particularly lethal at doses close to their effective amounts. The toxicity of substances depends on multiple factors, including dose, exposure duration, chemical structure, and individual factors, with environmental toxins and mycotoxins posing significant risks through various mechanisms.

Adverse Drug Reactions (ADRs) are harmful and unintended responses to medications, beyond their therapeutic effects, and can result from prescribed, over-the-counter, or illicit drugs. Type A ADRs are dose-related and predictable, often resulting from the drug's pharmacological action, with common examples including hypoglycemia from diabetes medication or tachycardia from asthma drugs. Type B ADRs are not dose-related, unpredictable, and often severe, affecting organs like the liver or skin; they include idiosyncratic or allergy-like reactions and are influenced by genetic and environmental factors. Additional classifications (C, D, E, F) cover a range of reactions from dose- and time-dependent effects (C), delayed reactions like carcinogenesis (D), withdrawal symptoms (E), to unexpected therapy failure (F). ADRs can be acute, subacute, or chronic based on onset, with severity ranging from mild to life-threatening, with severe cases requiring significant medical intervention or leading to permanent damage.

Drug toxicity, often resulting from an overdose, refers to the harmful effects that a chemical substance can have on an organism. These effects may target specific organs, such as the liver, or impact the CNS.

For instance, an over-the-counter painkiller overdose can cause adverse reactions, such as liver damage, stomach bleeding, and kidney disease.

On the other hand, an adverse drug reaction, or ADR, is a harmful and unintended response to a drug when used within its therapeutic window.

They can be acute, starting within 1 hour; subacute, happening within 24 hours; or latent reactions, appearing weeks to months post-exposure.

For example, antihypertensive drugs may cause hypotension, leading to dizziness or light-headedness.

ADRs can be classified into six types, labeled A through F.