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Q.How are drugs classified ?

Tamil Nadu DgeTamil Nadu HSC (DGE) Board 2025Subjective· 2mImportance★★★★★
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Since a single drug can be described in several different useful ways, drugs are classified on the basis of at least four criteria: the effect they produce, how they act at the molecular level, their chemical structure, and the specific biological target they bind to.

Drugs (chemicals of low molecular mass, 100100–500 u500\ u, that interact with macromolecular targets to produce a biological response) are classified in several complementary ways:

  1. On the basis of pharmacological effect: classified according to the physiological effect they produce, e.g. analgesics (relieve pain), antipyretics (reduce fever), antiseptics, antibiotics. This classification is useful for medical practitioners as it suggests the drug to use for a particular ailment/symptom.
  2. On the basis of drug action: classified according to the specific biochemical mechanism by which they produce their effect, e.g. all antihistamines that inhibit the action of histamine are grouped together, regardless of their differing chemical structures.
  3. On the basis of chemical structure: classified according to a common structural feature/skeleton they share, e.g. sulphonamides (containing the sulphonamide group) share similar properties and side effects. …

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