Question
Classify drugs based on their therapeutic action — analgesics, antibiotics, antiseptics, antacids, antihistamines, and tranquilizers. Give examples and mechanisms.
(NEET and CBSE 12 — drug classification is a direct-recall scoring topic)
Solution — Step by Step
Non-narcotic analgesics: Aspirin, ibuprofen, paracetamol. They inhibit prostaglandin synthesis (by blocking COX enzymes). Reduce pain and inflammation without causing addiction.
Narcotic analgesics: Morphine, codeine, heroin. They bind to opioid receptors in the CNS. Very effective for severe pain but highly addictive.
Antibiotics: Kill or inhibit bacteria. Two types:
- Bactericidal: Kill bacteria (penicillin, aminoglycosides)
- Bacteriostatic: Inhibit growth (erythromycin, tetracycline, chloramphenicol)
Broad-spectrum antibiotics work against many bacterial types (ampicillin). Narrow-spectrum target specific groups (penicillin G).
Antiseptics: Applied on living tissue (wounds, skin). Examples: Dettol (chloroxylenol), tincture of iodine, boric acid.
Disinfectants: Applied on non-living surfaces (floors, instruments). Examples: phenol (1%), chlorine, SO2 in water supplies.
Same chemical at different concentrations: 0.2% phenol = antiseptic, 1% phenol = disinfectant.
| Category | Action | Examples |
|---|---|---|
| Antacids | Neutralise excess stomach acid | Ranitidine, cimetidine, aluminium hydroxide |
| Antihistamines | Block histamine receptors (reduce allergy) | Brompheniramine, terfenadine |
| Tranquilizers | Reduce anxiety, calm the mind | Valium (diazepam), chlordiazepoxide |
| Antifertility drugs | Prevent conception | Norethindrone, ethynylestradiol |
| Antimicrobials | Broad term for anti-infection drugs | Sulphonamides, ciprofloxacin |
graph TD
A[Drug Classification] --> B["Analgesics: Pain"]
A --> C["Antibiotics: Bacteria"]
A --> D["Antiseptics: Living tissue"]
A --> E["Antacids: Stomach acid"]
A --> F["Antihistamines: Allergy"]
A --> G["Tranquilizers: Anxiety"]
B --> H["Non-narcotic: Aspirin"]
B --> I["Narcotic: Morphine"]
C --> J["Bactericidal: Penicillin"]
C --> K["Bacteriostatic: Tetracycline"]Why This Works
Drug classification by therapeutic action is how pharmacology organises thousands of drugs into manageable categories. Each category targets a specific physiological problem — pain (analgesics), infection (antibiotics), excess acid (antacids), immune overreaction (antihistamines).
The mechanism matters: antacids work in two ways. Sodium bicarbonate directly neutralises HCl. Ranitidine and cimetidine are H2-receptor blockers — they prevent acid secretion. The second approach is more effective for chronic conditions because it addresses the cause, not just the symptom.
Alternative Method
For NEET, the most-tested matchings:
- Aspirin = analgesic + antipyretic + anti-inflammatory (blocks COX)
- Penicillin = antibiotic (discovered by Alexander Fleming)
- Chloramphenicol = broad-spectrum, bacteriostatic antibiotic
- Equanil = tranquilizer
- Bithionol = antiseptic in soaps
Know these five cold — they appear almost every year.
Common Mistake
Students confuse antiseptics and disinfectants. The key difference is the surface of application: antiseptics go on living tissue (skin, wounds), disinfectants go on non-living surfaces (floors, instruments, toilets). The same chemical (like phenol) can serve as both — it depends on concentration. Dilute phenol (0.2%) is safe for skin; concentrated phenol (1%) would damage tissue and is used on floors.
Also, aspirin is NOT a narcotic analgesic. Aspirin is a non-narcotic analgesic (no addiction risk). Narcotics (morphine, heroin) work on brain opioid receptors and cause addiction. NEET tests this classification frequently.