Mechanism
Cell wall synthesis inhibition
Class
Penicillins
Key Examples
Penicillin G, Amoxicillin, Ampicillin, Piperacillin
Bactericidal / Bacteriostatic
Bactericidal
NotesAll Years (1st-Final)All UniversitiesAntibiotic
Antibiotic Classification Chart for MBBS
Antibiotics are one of the highest-yield topics in Pharmacology and Microbiology, appearing across MBBS Phase 2 and Final Year university papers. This chart organises all major antibiotic classes by mechanism of action, the format most commonly tested in Indian university exams. SME-reviewed. Updated 2026.
Open in GeckoMed appAntibiotic Classification Chart
Classification by Mechanism of Action
| Mechanism | Class | Key Examples | Bactericidal / Bacteriostatic |
|---|---|---|---|
| Cell wall synthesis inhibition | Penicillins | Penicillin G, Amoxicillin, Ampicillin, Piperacillin | Bactericidal |
| Cell wall synthesis inhibition | Cephalosporins (Generation 1 to 5) | Gen 1: Cephalexin; Gen 2: Cefuroxime; Gen 3: Ceftriaxone, Cefotaxime; Gen 4: Cefepime; Gen 5: Ceftaroline | Bactericidal |
| Cell wall synthesis inhibition | Carbapenems | Imipenem, Meropenem, Ertapenem | Bactericidal |
| Cell wall synthesis inhibition | Monobactams | Aztreonam | Bactericidal |
| Cell wall synthesis inhibition (D-Ala-D-Ala binding) | Glycopeptides | Vancomycin, Teicoplanin | Bactericidal |
| 30S ribosomal subunit inhibition (irreversible) | Aminoglycosides | Gentamicin, Streptomycin, Amikacin, Tobramycin | Bactericidal |
| 30S ribosomal subunit inhibition (reversible) | Tetracyclines | Tetracycline, Doxycycline, Minocycline | Bacteriostatic |
| 50S ribosomal subunit inhibition | Macrolides | Erythromycin, Azithromycin, Clarithromycin | Bacteriostatic |
| 50S ribosomal subunit inhibition | Chloramphenicol | Chloramphenicol | Bacteriostatic |
| 50S ribosomal subunit inhibition | Lincosamides | Clindamycin | Bacteriostatic |
| 50S ribosomal subunit inhibition | Oxazolidinones | Linezolid | Bacteriostatic |
| DNA gyrase / Topoisomerase IV inhibition | Fluoroquinolones | Ciprofloxacin, Norfloxacin, Levofloxacin, Moxifloxacin | Bactericidal |
| RNA polymerase inhibition | Rifamycins | Rifampicin | Bactericidal |
| Folate synthesis inhibition (DHPS) | Sulfonamides | Sulfamethoxazole, Co-trimoxazole(Bactericidal) | Bacteriostatic |
| Folate synthesis inhibition (DHFR) | Diaminopyrimidines | Trimethoprim | Bacteriostatic |
| Anaerobic DNA strand disruption | Nitroimidazoles | Metronidazole, Tinidazole | Bactericidal |
| Cell membrane disruption | Polymyxins | Polymyxin B, Colistin | Bactericidal |
Mechanism
Cell wall synthesis inhibition
Class
Cephalosporins (Generation 1 to 5)
Key Examples
Gen 1: Cephalexin; Gen 2: Cefuroxime; Gen 3: Ceftriaxone, Cefotaxime; Gen 4: Cefepime; Gen 5: Ceftaroline
Bactericidal / Bacteriostatic
Bactericidal
Mechanism
Cell wall synthesis inhibition
Class
Carbapenems
Key Examples
Imipenem, Meropenem, Ertapenem
Bactericidal / Bacteriostatic
Bactericidal
Mechanism
Cell wall synthesis inhibition
Class
Monobactams
Key Examples
Aztreonam
Bactericidal / Bacteriostatic
Bactericidal
Mechanism
Cell wall synthesis inhibition (D-Ala-D-Ala binding)
Class
Glycopeptides
Key Examples
Vancomycin, Teicoplanin
Bactericidal / Bacteriostatic
Bactericidal
Mechanism
30S ribosomal subunit inhibition (irreversible)
Class
Aminoglycosides
Key Examples
Gentamicin, Streptomycin, Amikacin, Tobramycin
Bactericidal / Bacteriostatic
Bactericidal
Mechanism
30S ribosomal subunit inhibition (reversible)
Class
Tetracyclines
Key Examples
Tetracycline, Doxycycline, Minocycline
Bactericidal / Bacteriostatic
Bacteriostatic
Mechanism
50S ribosomal subunit inhibition
Class
Macrolides
Key Examples
Erythromycin, Azithromycin, Clarithromycin
Bactericidal / Bacteriostatic
Bacteriostatic
Mechanism
50S ribosomal subunit inhibition
Class
Chloramphenicol
Key Examples
Chloramphenicol
Bactericidal / Bacteriostatic
Bacteriostatic
Mechanism
50S ribosomal subunit inhibition
Class
Lincosamides
Key Examples
Clindamycin
Bactericidal / Bacteriostatic
Bacteriostatic
Mechanism
50S ribosomal subunit inhibition
Class
Oxazolidinones
Key Examples
Linezolid
Bactericidal / Bacteriostatic
Bacteriostatic
Mechanism
DNA gyrase / Topoisomerase IV inhibition
Class
Fluoroquinolones
Key Examples
Ciprofloxacin, Norfloxacin, Levofloxacin, Moxifloxacin
Bactericidal / Bacteriostatic
Bactericidal
Mechanism
RNA polymerase inhibition
Class
Rifamycins
Key Examples
Rifampicin
Bactericidal / Bacteriostatic
Bactericidal
Mechanism
Folate synthesis inhibition (DHPS)
Class
Sulfonamides
Key Examples
Sulfamethoxazole, Co-trimoxazole(Bactericidal)
Bactericidal / Bacteriostatic
Bacteriostatic
Mechanism
Folate synthesis inhibition (DHFR)
Class
Diaminopyrimidines
Key Examples
Trimethoprim
Bactericidal / Bacteriostatic
Bacteriostatic
Mechanism
Anaerobic DNA strand disruption
Class
Nitroimidazoles
Key Examples
Metronidazole, Tinidazole
Bactericidal / Bacteriostatic
Bactericidal
Mechanism
Cell membrane disruption
Class
Polymyxins
Key Examples
Polymyxin B, Colistin
Bactericidal / Bacteriostatic
Bactericidal
Quick Reference: Bacteriostatic vs Bactericidal
| Bactericidal | Bacteriostatic |
|---|---|
| Penicillins, Cephalosporins, Carbapenems | Tetracyclines, Macrolides |
| Aminoglycosides, Fluoroquinolones | Chloramphenicol, Clindamycin |
| Vancomycin, Rifampicin | Sulfonamides, Trimethoprim |
| Metronidazole, Polymyxins | Linezolid |
Bactericidal
Penicillins, Cephalosporins, Carbapenems
Bacteriostatic
Tetracyclines, Macrolides
Bactericidal
Aminoglycosides, Fluoroquinolones
Bacteriostatic
Chloramphenicol, Clindamycin
Bactericidal
Vancomycin, Rifampicin
Bacteriostatic
Sulfonamides, Trimethoprim
Bactericidal
Metronidazole, Polymyxins
Bacteriostatic
Linezolid
Exam Tip: Bactericidal antibiotics are preferred in immunocompromised patients and in conditions such as meningitis, endocarditis, and septicaemia.
How to Use This Chart for Exams
1. Learn mechanism first, names second. University examiners ask "classify antibiotics with examples" far more often than they ask about individual drugs. Knowing which class each drug belongs to lets you answer any classification question without memorising a separate list for each question type.
2. Group beta-lactams together. Penicillins, cephalosporins, carbapenems, and monobactams all share the beta-lactam ring and act by inhibiting cell wall synthesis via penicillin-binding proteins (PBPs). Treat them as one family in your answer, then distinguish by spectrum and generation.
3. Pair the chart with the bactericidal vs bacteriostatic table. Many five-mark questions ask for this distinction specifically. The quick reference table above is the fastest way to revise this point before an exam.
4. Cross-reference with Microbiology for clinical application. Knowing which antibiotic is used for which organism (e.g., Vancomycin for methicillin-resistant Staphylococcus aureus, Metronidazole for anaerobes and protozoa) earns marks in both Pharmacology and Microbiology papers. See the Antibiotic Sensitivity Chart for organism-to-drug pairing.
How This Topic Appears in University Papers
Antibiotic classification is a recurring question across Pharmacology and Microbiology papers in all seven GeckoMed target universities.
- "Classify beta lactam antibiotics. Enumerate the mechanism of action, adverse
- effects and therapeutic uses of penicillins." (10 marks)
- "Write a short note on beta-lactam antibiotics." (5 marks)
- "Enumerate bactericidal and bacteriostatic antibiotics." (5 marks)
- "Write a short note on aminoglycosides." (5 marks)
- "Discuss the mechanism of action of penicillin." (5 marks)
Practice with past papers on GeckoMed: RGUHS Pharmacology Question Papers | KNRUHS Pharmacology Question Papers | TNMGRMU Pharmacology Question Papers
Frequently Asked Questions
What is the most important antibiotic classification for MBBS exams?
Classification by mechanism of action is the most commonly tested format in Indian university Pharmacology and Microbiology papers. The chart above covers all major classes and is structured to match the way examiners expect answers to be written.
Which MBBS year is antibiotic classification covered in?
Antibiotics are covered primarily in Phase 2 (2nd Year) in both Pharmacology and Microbiology. However, clinical application questions appear in Final Year General Medicine and General Surgery papers as well, making this topic relevant across all four years.
How do I distinguish bactericidal from bacteriostatic antibiotics quickly?
Use the quick reference table in this chart. A practical rule to remember: aminoglycosides, beta-lactams, fluoroquinolones, vancomycin, rifampicin, metronidazole, and polymyxins are bactericidal. Tetracyclines, macrolides, chloramphenicol, clindamycin, sulfonamides, and linezolid are bacteriostatic.
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