Toxicology and its branches. Classification of poisons based on actions and lethal doses, types of antidotes.

Toxicology is the branch of science that deals with the harmful effects of chemical, physical and biological agents on living organisms. In simple terms, it is the study of poisons, their toxic effects, mechanisms of action, detection, prevention and treatment. The subject is closely associated with pharmacology because the difference between a medicine and a poison often depends on the dose. This fundamental principle was given by Paracelsus, popularly known as the Father of Toxicology, who stated that “the dose makes the poison.”

Toxicology has several important branches, each dealing with a specific aspect of toxic substances. Clinical toxicology focuses on the diagnosis and treatment of poisoning in patients, whereas forensic toxicology deals with the detection and interpretation of poisons in medico-legal investigations. Environmental toxicology studies the harmful effects of pollutants present in air, water and soil, while occupational toxicology is concerned with exposure to toxic substances in workplaces. Other important areas include analytical, regulatory and experimental toxicology.

Poisons may be classified according to their action on the body, such as corrosive, irritant, neurotoxic, asphyxiant and systemic poisons. Understanding the mechanism and site of action of a poison is important for predicting its toxic effects and selecting appropriate treatment. Another important concept is the lethal dose, particularly LD₅₀, which is commonly used as an indicator of acute toxicity. Generally, a lower LD₅₀ value indicates greater acute toxicity.

The management of poisoning also involves the use of antidotes, which may act by physical, chemical or physiological mechanisms. Important examples include activated charcoal, naloxone, atropine, pralidoxime, N-acetylcysteine and various chelating agents.

The following easy-to-revise notes and MCQs will help pharmacy students understand these fundamental concepts and prepare for competitive examinations such as GPAT, NIPER, UPSC Drug Inspector, AIIMS Pharmacist, Railway Pharmacist, SSC, ESIC and State Pharmacist examinations.

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