Therapeutic Action of Different Classes of Drugs — Revision Notes

⚡ 30-Second Revision

Antacids — Neutralize stomach $HCl$. Ex: $Mg(OH)_2$, $Al(OH)_3$.
Antihistamines — Block histamine receptors. H1 (allergies): Cetirizine. H2 (acidity): Cimetidine.
Tranquilizers — Enhance GABA activity in CNS. Ex: Diazepam.
Analgesics

- Non-narcotic (NSAIDs): Inhibit COX enzymes, reduce prostaglandins. Ex: Aspirin, Ibuprofen. - Narcotic (Opioids): Act on opioid receptors. Ex: Morphine.

Antimicrobials

- Antibiotics: Kill/inhibit microbes selectively. Ex: Penicillin (cell wall), Tetracycline (protein synthesis). - Antiseptics: On living tissues. Ex: Dettol, Iodine. - Disinfectants: On inanimate objects. Ex: Chlorine, Phenol.

Antifertility Drugs — Synthetic hormones, inhibit ovulation. Ex: Norethindrone (progesterone), Ethynylestradiol (estrogen).

2-Minute Revision

The therapeutic action of drugs hinges on their interaction with specific biological targets to produce beneficial effects. Antacids, like magnesium hydroxide, work by direct neutralization of stomach acid, providing symptomatic relief from acidity.

Antihistamines, such as Cimetidine (H2-blocker for acidity) or Cetirizine (H1-blocker for allergies), function by antagonizing histamine receptors, preventing histamine's natural effects. Tranquilizers, exemplified by Diazepam, calm the central nervous system by enhancing the inhibitory action of GABA, leading to reduced anxiety and sedation.

Analgesics alleviate pain; NSAIDs like Aspirin do so by inhibiting COX enzymes and prostaglandin synthesis, while narcotic analgesics like Morphine act on opioid receptors. Antimicrobials are a broad category: antibiotics (e.

g., Penicillin) selectively target bacterial processes like cell wall synthesis; antiseptics (e.g., Dettol) are applied to living tissues to prevent infection; and disinfectants (e.g., Chlorine) are used on inanimate objects to kill microbes.

Antifertility drugs, containing synthetic estrogen and progesterone derivatives like Norethindrone, prevent conception primarily by inhibiting ovulation.

5-Minute Revision

Understanding the therapeutic action of different drug classes is fundamental to NEET Chemistry. Drugs exert their effects by binding to specific biological macromolecules (receptors, enzymes, nucleic acids) – these are their 'targets'. An agonist activates a receptor, mimicking natural messengers, while an antagonist blocks it. Enzyme inhibitors reduce enzyme activity.

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Antacids — These are bases that neutralize excess stomach acid ($HCl$). For example, $Mg(OH)_2 + 2HCl \rightarrow MgCl_2 + 2H_2O$. They provide quick relief but don't stop acid production. Common examples are Milk of Magnesia and Aluminium Hydroxide gel.
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Antihistamines — Histamine causes allergic reactions and stimulates acid secretion. Antihistamines block histamine receptors. H1-antagonists (e.g., Cetirizine, Fexofenadine) treat allergies. H2-antagonists (e.g., Cimetidine, Ranitidine) reduce stomach acid secretion.
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Tranquilizers — These drugs reduce anxiety and induce sleep by enhancing the activity of GABA, an inhibitory neurotransmitter in the CNS. Benzodiazepines (e.g., Diazepam) bind to GABA-A receptors, increasing chloride ion influx and hyperpolarizing neurons.
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Analgesics (Pain Relievers)

* Non-narcotic (NSAIDs): Aspirin, Ibuprofen, Paracetamol. They inhibit cyclooxygenase (COX) enzymes, reducing the synthesis of prostaglandins (which cause pain, inflammation, fever). Aspirin irreversibly inhibits COX. * Narcotic (Opioids): Morphine, Codeine. They bind to opioid receptors in the CNS, mimicking natural endorphins for potent pain relief, but are addictive.

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Antimicrobials — Kill or inhibit microorganisms.

* Antibiotics: Selectively toxic to microbes. Penicillins inhibit bacterial cell wall synthesis. Tetracyclines inhibit bacterial protein synthesis. Effective against bacteria, not viruses. * Antiseptics: Applied to living tissues (e.g., Dettol, Iodine tincture) to prevent infection. * Disinfectants: Applied to inanimate objects (e.g., Chlorine, Phenol) to kill microbes; too toxic for living tissue.

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Antifertility Drugs — Oral contraceptives containing synthetic estrogen (e.g., Ethynylestradiol) and progesterone (e.g., Norethindrone) derivatives. They primarily inhibit ovulation by suppressing gonadotropin release, preventing conception.

Remember to differentiate between antiseptics and disinfectants based on their application site and toxicity. Also, distinguish between H1 and H2 antihistamines based on their target receptors and uses.

Prelims Revision Notes

Therapeutic Action of Different Classes of Drugs - NEET Revision Notes

I. Drug-Target Interaction Basics:

Drugs interact with biological macromolecules (receptors, enzymes, nucleic acids) called drug targets.
Agonist — Binds to receptor, activates it, mimics natural messenger (e.g., Morphine on opioid receptors).
Antagonist — Binds to receptor, blocks natural messenger, inhibits response (e.g., Antihistamines).
Enzyme Inhibitors — Block active site or alter enzyme conformation to reduce activity.

II. Key Drug Classes and Their Actions:

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Antacids:

* Action: Neutralize excess $HCl$ in stomach. * Mechanism: Acid-base reaction. $Mg(OH)_2 + 2HCl \rightarrow MgCl_2 + 2H_2O$. * Examples: Magnesium hydroxide ($Mg(OH)_2$), Aluminium hydroxide ($Al(OH)_3$), Sodium bicarbonate ($NaHCO_3$). * Note: $Mg(OH)_2$ is a laxative, $Al(OH)_3$ causes constipation; often used in combination.

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Antihistamines:

* Action: Block histamine receptors. * Histamine: Potent vasodilator, involved in allergies and $HCl$ secretion. * H1-Antagonists: Treat allergies (runny nose, itching). * Examples: Cetirizine, Fexofenadine, Diphenhydramine. * H2-Antagonists: Reduce stomach acid secretion. * Examples: Cimetidine, Ranitidine (now largely replaced).

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Tranquilizers (Anxiolytics/Sedatives/Hypnotics):

* Action: Reduce anxiety, induce calmness, promote sleep. * Mechanism: Enhance activity of GABA (gamma-aminobutyric acid), an inhibitory neurotransmitter in CNS. * Examples: Benzodiazepines (Diazepam, Alprazolam), Barbiturates.

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Analgesics (Pain Relievers):

* Non-narcotic (Non-addictive): * Action: Relieve pain, reduce fever (antipyretic), reduce inflammation (anti-inflammatory). * Mechanism: Inhibit cyclooxygenase (COX) enzymes, reducing prostaglandin synthesis. * Examples: Aspirin (irreversible COX inhibitor), Ibuprofen, Paracetamol (Acetaminophen). * Narcotic (Addictive): * Action: Potent pain relief. * Mechanism: Bind to opioid receptors in CNS. * Examples: Morphine, Codeine, Heroin (diacetylmorphine).

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Antimicrobials:

* Antibiotics: Kill or inhibit growth of microorganisms (bacteria, fungi). * Selective Toxicity: Target microbial structures/processes unique to them. * Examples: Penicillins (inhibit bacterial cell wall synthesis), Tetracyclines (inhibit bacterial protein synthesis), Fluoroquinolones (inhibit bacterial DNA replication).

* Note: Ineffective against viruses. * Antiseptics: Applied to living tissues (skin, wounds) to prevent infection. * Examples: Dettol (Chloroxylenol + Terpineol), Savlon (Chlorhexidine + Cetrimide), Iodine tincture, Boric acid.

* Disinfectants: Applied to inanimate objects (floors, instruments) to kill microbes; too toxic for living tissues. * Examples: Chlorine, Phenol, Formaldehyde.

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Antifertility Drugs (Oral Contraceptives):

* Action: Prevent conception. * Mechanism: Primarily inhibit ovulation by suppressing gonadotropin (LH, FSH) release. * Components: Synthetic derivatives of estrogen and progesterone. * Examples: Norethindrone (synthetic progesterone), Ethynylestradiol (synthetic estrogen).

III. Key Distinctions:

Antiseptic vs. Disinfectant — Living tissue vs. inanimate objects; lower vs. higher toxicity.
H1 vs. H2 Antihistamines — Allergy vs. acidity treatment.
Agonist vs. Antagonist — Activates vs. blocks receptor.

IV. NEET Focus:

Memorize specific examples for each class.
Understand the primary mechanism of action for each class/drug.
Be able to differentiate between similar-sounding terms.

Vyyuha Quick Recall

All Animals Try Always And Always For Food.

Antacids: Acid neutralization
Antihistamines: Allergy/Acidity (H1/H2 receptor block)
Tranquilizers: Tranquility (GABA enhancement)
Analgesics: Allay pain (COX inhibition/Opioid receptors)
Antimicrobials: Against microbes (various mechanisms)
Antifertility: Avoid fertility (Hormonal control)
For Food: (Just a filler to make it catchy and complete the sentence!)