Antibiotics are chemical substances that kill bacteria or stop their growth. They are used to treat bacterial infections in humans, animals, and sometimes plants. Antibiotics work by targeting structures or processes that are essential for bacterial survival, making them powerful tools in infectious disease management.
What Are Antibiotics?
Antibiotics may be:
- Natural – produced by microorganisms like fungi or bacteria
- Semi-synthetic – chemically modified natural antibiotics
- Synthetic – completely made in the laboratory
They can have either:
- Bactericidal action – kill bacteria
- Bacteriostatic action – inhibit growth of bacteria
Classification of Antibiotics
1. Based on Chemical Structure
- Penicillins
- Cephalosporins
- Aminoglycosides
- Tetracyclines
- Macrolides
- Quinolones
- Chloramphenicol
- Glycopeptides
2. Based on Mechanism of Action
- Inhibit cell wall synthesis – Penicillins, Cephalosporins, Vancomycin
- Inhibit protein synthesis – Tetracyclines, Aminoglycosides, Macrolides
- Inhibit nucleic acid synthesis – Quinolones, Rifampicin
- Antimetabolites – Sulfonamides
- Inhibit cell membrane function – Polymyxins
Important Antibiotic Groups
1) Penicillins
Penicillins are β-lactam antibiotics.
Mechanism: Inhibit bacterial cell wall synthesis by blocking transpeptidase enzymes.
Examples: Penicillin G, Amoxicillin, Ampicillin.
Uses: Skin infections, respiratory infections, and streptococcal infections.
2) Cephalosporins
Structurally related to penicillins but broader in spectrum.
Generations: 1st to 5th generation, increasing Gram-negative coverage with each generation.
Uses: UTIs, respiratory infections, surgical prophylaxis.
3) Tetracyclines
Mechanism: Inhibit protein synthesis by binding to the 30S ribosomal subunit.
Uses: Acne, cholera, atypical pneumonia.
Example: Doxycycline.
4) Aminoglycosides
Mechanism: Irreversibly inhibit protein synthesis.
Uses: Serious Gram-negative infections.
Examples: Gentamicin, Amikacin.
5) Macrolides
Mechanism: Bind to the 50S ribosomal subunit and block protein synthesis.
Uses: Respiratory infections, skin infections.
Examples: Erythromycin, Azithromycin.
6) Quinolones
Mechanism: Inhibit DNA gyrase and topoisomerase IV.
Uses: UTIs, GI infections.
Examples: Ciprofloxacin, Levofloxacin.
7) Chloramphenicol
Mechanism: Inhibits protein synthesis at 50S ribosome.
Use: Typhoid fever.
Caution: Bone marrow suppression.
8) Glycopeptides
Mechanism: Inhibit cell wall synthesis.
Example: Vancomycin.
Use: MRSA infections.
Antibiotic Resistance
Bacteria can become resistant to antibiotics due to:
- Overuse or misuse of antibiotics
- Incomplete treatment courses
- Genetic mutations
- Transfer of resistance genes between bacteria
Adverse Effects of Antibiotics
- Allergic reactions (rash, anaphylaxis)
- Gastrointestinal upset
- Kidney or liver toxicity (with some drugs)
- Superinfections (e.g., fungal infections)
Detailed Notes:
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