Drugs and their Classification — Revision Notes

⚡ 30-Second Revision

Drugs: — Chemical substances interacting with macromolecular targets to produce biological response.
Medicines: — Drugs with therapeutic and desirable effects.
Classification by Pharmacological Effect:

* Antacids: Neutralize stomach acid (e.g., $\text{Mg(OH)}_2$, $\text{Al(OH)}_3$). * Antihistamines: Block histamine receptors (e.g., Cetirizine, Fexofenadine). * Analgesics: Pain relievers (e.

g., Aspirin, Paracetamol). * Antipyretics: Reduce fever (e.g., Aspirin, Paracetamol). * Tranquilizers: Reduce anxiety (e.g., Diazepam, Barbiturates). * Antimicrobials: Kill/inhibit microbes.

* Antibiotics: Target bacteria (e.g., Penicillin - bactericidal; Tetracycline - bacteriostatic). * Antiseptics: For living tissues (e.g., Dettol, Tincture of Iodine). * Disinfectants: For inanimate objects (e.

g., 1% Phenol, Chlorine). * Antifertility Drugs: Prevent conception (e.g., Norethindrone, Ethynylestradiol).

Classification by Molecular Target: — Enzymes, Receptors (Agonists/Antagonists).
Agonist: — Mimics natural messenger, activates receptor.
Antagonist: — Blocks natural messenger, prevents receptor activation.

2-Minute Revision

Drugs are low molecular mass chemicals that interact with biological targets (proteins, nucleic acids, etc.) to produce a response. If beneficial, they are medicines. Drugs are classified in several ways.

By pharmacological effect, we have Antacids (neutralize stomach acid, e.g., Milk of Magnesia), Antihistamines (block histamine, e.g., Cetirizine; first-gen are sedating, second-gen are non-sedating), Analgesics (pain relief, e.

g., Aspirin), Antipyretics (fever reduction, e.g., Paracetamol), and Tranquilizers (reduce anxiety, e.g., Diazepam). Antimicrobials are a broad class: Antibiotics (target bacteria, e.g., Penicillin - bactericidal; Tetracycline - bacteriostatic; can be broad or narrow spectrum), Antiseptics (for living tissues, e.

g., Dettol, Tincture of Iodine), and Disinfectants (for inanimate objects, e.g., 1% Phenol). Antifertility drugs (e.g., Norethindrone) are synthetic hormones preventing conception. Drugs also classify by molecular target: enzymes (inhibitors) or receptors (agonists activate, antagonists block).

5-Minute Revision

Drugs are chemical substances that interact with biological macromolecules (like enzymes, receptors, DNA) in the body to produce a biological response. When this response is therapeutic, they are called medicines. Their classification is vital for understanding their use and mechanism.

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Based on Pharmacological Effect: — This groups drugs by what they do.

* Antacids: Neutralize excess stomach acid. Examples: Magnesium hydroxide ($ext{Mg(OH)}_2$), Aluminium hydroxide ($ext{Al(OH)}_3$). They provide symptomatic relief from acidity. * Antihistamines: Counteract histamine effects, used for allergies.

First-generation (e.g., Diphenhydramine) cause sedation; second-generation (e.g., Fexofenadine, Cetirizine) are non-sedating as they don't cross the blood-brain barrier easily. Note: $ext{H}_2$-receptor antagonists (e.

g., Cimetidine, Ranitidine) reduce stomach acid production, distinct from $ext{H}_1$ antihistamines for allergies. * Analgesics: Reduce pain. Non-narcotic (non-addictive) like Aspirin and Paracetamol.

Narcotic (addictive) like Morphine. * Antipyretics: Reduce fever. Many analgesics (Aspirin, Paracetamol) also act as antipyretics. * Tranquilizers (Neurologically Active Drugs): Relieve stress and anxiety by acting on the CNS.

Examples: Barbiturates (Veronal, Luminal), Benzodiazepines (Diazepam, Chlordiazepoxide). * Antimicrobials: Kill or inhibit microorganisms. * Antibiotics: Specifically target bacteria. Can be bactericidal (kill, e.

g., Penicillin) or bacteriostatic (inhibit growth, e.g., Tetracycline). Also broad-spectrum (wide range) or narrow-spectrum (specific types). * Antiseptics: Applied to living tissues (e.g., Dettol, Tincture of Iodine, dilute Boric acid).

* Disinfectants: Applied to inanimate objects (e.g., 1% Phenol, Chlorine). Crucially, some substances like phenol can be antiseptic at low concentrations (0.2%) and disinfectant at high (1%). * Antifertility Drugs: Synthetic hormones (estrogen/progesterone derivatives) used as contraceptives (e.

g., Norethindrone, Ethynylestradiol).

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Based on Molecular Target: — Drugs interact with specific macromolecules.

* Enzymes: Drugs can inhibit enzyme activity (e.g., Sulfa drugs inhibit bacterial folic acid synthesis). * Receptors: Drugs can be agonists (mimic natural messenger, activate receptor) or antagonists (block natural messenger, prevent receptor activation).

Worked Mini-Example: If a question asks, 'Which of the following is a broad-spectrum antibiotic?', and options are Penicillin G, Chloramphenicol, Amoxicillin, and Erythromycin. You should recall that Penicillin G is narrow-spectrum, Amoxicillin and Erythromycin are relatively broad, but Chloramphenicol is known for its very broad spectrum against both Gram-positive and Gram-negative bacteria, and rickettsiae.

So, Chloramphenicol would be the best answer, emphasizing the need for specific examples.

Prelims Revision Notes

For NEET, 'Drugs and their Classification' requires strong factual recall. Focus on these key points:

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Definition: — Drugs are low molecular mass chemicals (100-500 amu) interacting with macromolecular targets (proteins, nucleic acids, lipids, carbohydrates) to produce a biological response. Medicines are therapeutic drugs.
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Classification by Pharmacological Effect (Most Tested):

* Antacids: Neutralize stomach acid. Examples: $\text{Mg(OH)}_2$, $\text{Al(OH)}_3$, $\text{NaHCO}_3$. * Antihistamines: Block histamine receptors. $\text{H}_1$ blockers for allergies (e.g., Cetirizine, Fexofenadine - non-sedating; Diphenhydramine - sedating).

$\text{H}_2$ blockers for stomach acid reduction (e.g., Cimetidine, Ranitidine). * Analgesics: Pain relievers. Non-narcotic (Aspirin, Paracetamol). Narcotic (Morphine, Codeine). * Antipyretics: Reduce fever (Aspirin, Paracetamol).

* Tranquilizers (Neurologically Active): Reduce anxiety/stress. Examples: Barbiturates (Veronal, Luminal), Benzodiazepines (Diazepam, Chlordiazepoxide). * Antimicrobials: Kill/inhibit microbes.

* Antibiotics: Target bacteria. Bactericidal (kills, e.g., Penicillin, Amoxicillin). Bacteriostatic (inhibits growth, e.g., Tetracycline, Chloramphenicol). Broad-spectrum (e.g., Chloramphenicol, Tetracycline).

Narrow-spectrum (e.g., Penicillin G). * Antiseptics: For living tissues. Examples: Dettol (Chloroxylenol + Terpineol), Savlon (Chlorhexidine + Cetrimide), Tincture of Iodine (2-3% $\text{I}_2$ in alcohol-water), dilute Boric acid, 0.

2% Phenol. * Disinfectants: For inanimate objects. Examples: 1% Phenol, Chlorine (0.2-0.4 ppm), $\text{SO}_2$. * Antifertility Drugs: Hormonal contraceptives. Examples: Norethindrone, Ethynylestradiol (Novestrol).

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Classification by Molecular Target:

* Enzymes: Drugs act as inhibitors (competitive/non-competitive). * Receptors: Drugs act as agonists (mimic natural messenger) or antagonists (block natural messenger).

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Key Distinctions: — Antiseptic vs. Disinfectant (application site, toxicity, concentration). Bactericidal vs. Bacteriostatic (kill vs. inhibit growth). Agonist vs. Antagonist (activate vs. block receptor).

Vyyuha Quick Recall

To remember key drug classes and their actions: All Animals Always Try And Make All Friends.

Antacids: Neutralize acid
Antihistamines: Block histamine
Analgesics: Relieve pain
Tranquilizers: Reduce anxiety
Antimicrobials: Fight microbes
Make (Molecular Targets): Enzymes/Receptors
All (Agonists/Antagonists): Receptor activators/blockers
Friends (Antifertility): Prevent conception