Drugs and their Classification — Core Principles

Core Principles

Drugs are chemical substances, typically of low molecular mass, that interact with biological macromolecules in the body to produce a biological response. When these responses are therapeutic, the drugs are termed medicines.

Drug classification is essential for understanding their action and use. Key classification methods include: by pharmacological effect (what they do, e.g., antacids, analgesics, antihistamines), by drug action or molecular target (how they work, e.

g., enzyme inhibitors, receptor agonists/antagonists), by chemical structure (common structural features, e.g., sulphonamides), and by molecular target (the specific macromolecule they bind to, e.g., proteins, nucleic acids).

Examples of drug classes include antacids (neutralize stomach acid), antihistamines (block histamine receptors), neurologically active drugs (affect CNS, e.g., tranquilizers), antimicrobials (kill/inhibit microbes, including antibiotics, antiseptics, disinfectants), and antifertility drugs (hormonal contraceptives).

Understanding these classifications and specific examples is crucial for NEET.

Important Differences

vs Antiseptics and Disinfectants

Aspect	This Topic	Antiseptics and Disinfectants
Application Site	Antiseptics: Applied to living tissues (skin, wounds, mucous membranes).	Disinfectants: Applied to inanimate objects (floors, instruments, surfaces).
Toxicity to Living Cells	Antiseptics: Relatively mild, safe for topical application on living tissues, minimal harm to host cells.	Disinfectants: Highly toxic to living cells, not safe for internal use or application on skin.
Purpose	Antiseptics: Prevent or inhibit the growth of microorganisms on living surfaces to reduce infection risk.	Disinfectants: Kill or destroy all microorganisms (except spores) on inanimate surfaces to sterilize or sanitize.
Concentration	Antiseptics: Used in lower, less concentrated forms.	Disinfectants: Often used in higher, more concentrated forms.
Examples	Antiseptics: Dettol, Savlon, Tincture of Iodine, Boric acid (dilute solution).	Disinfectants: 1% Phenol solution, Chlorine (0.2-0.4 ppm), Sulphur dioxide.

Antiseptics and disinfectants both aim to control microbial growth, but their fundamental difference lies in their application. Antiseptics are formulated to be safe for use on living tissues, inhibiting microbial growth without causing significant harm to host cells. Disinfectants, conversely, are much harsher chemicals designed to kill microorganisms on non-living surfaces and are toxic to living tissues. It's crucial to note that some substances, like phenol, can function as an antiseptic at low concentrations and a disinfectant at higher concentrations, highlighting the importance of concentration in determining their specific use.