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15th March 2024
An overview of the main antibiotic classes
| Antibiotic Classes | Examples | Mechanism | Spectrum | Notes |
|---|---|---|---|---|
| Penicillins | Amoxicillin, benzylpenicillin, flucloxacillin | Binds to transpeptidases, in turn disrupting the cell wall | Older penicillins (penicillin V) only gram +ve
Otherwise broad gram +ve/-ve and certain anaerobes |
Piperacillin / tazobactam has enhanced coverage of gram negatives including antipseudomonal activity |
| Cephalosporins
(5 generations) |
Cefpirome (4ᵗʰ), ceftriaxone (3ʳᵈ), cefalexin (1ˢᵗ) | Binds to transpeptidases, in turn disrupting the peptidoglycan cell wall | Broad
gram +ve/-ve As the generations increase wider gram -ve cover (up until 4ᵗʰ) |
|
| Glycopeptides | Vancomycin, teicoplanin | Binds to transpeptidases (d-alanyl-d-alanine) affecting cross-linking the cell wall | Gram +ve
Vancomycin for C. difficile |
Associated with an infusion reaction termed vancomycin flushing syndrome |
| Macrolides | Azithromycin, clarithromycin, erythromycin | Binds to the 50S ribosomal subunit interfering with protein synthesis | Broad
Gram +ve/-ve |
|
| Chloramphenicol | Chloramphenicol | Binds to 50S ribosomal subunit interfering with protein synthesis | Broad
Gram +ve/-ve and anaerobes |
If given premature babies or those < 2 weeks of age, risk of grey baby syndrome |
| Tetracyclines | Doxycycline, lymecycline | Binds to 30S ribosomal subunit interfering with protein synthesis | Broad
Gram +ve/-ve and atypicals |
Covers many protozoal infections |
| Aminoglycosides | Gentamicin, tobramycin | Binds to 30S ribosomal subunit interfering with protein synthesis | Mainly gram -ve | |
| Trimethoprim | Trimethoprim | Dihydrofolate reductase inhibitor halting bacterial folate synthesis | Broad
Gram +ve/-ve |
Combined with sulfamethoxazole to make co-trimoxazole used to treat PCP |
| Quinolones/Fluoroquinolones | Ciprofloxacin, ofloxacin | Inhibit nucleic acid synthesis by inhibiting DNA gyrase and topoisomerase IV | Mainly gram -ve and certain gram +ve | Ciprofloxacin is the only oral antibiotic that has antipseudomonal activity
Treatment for C. difficile |
| Metronidazole | Metronidazole | Inhibits bacterial DNA, causing breakage and destabilisation | Mainly used for anaerobes | Covers certain protozoal infections
Treatment for C. difficile |
| Oxazolidinones | Linezolid and tedizolid | Binds to the 23S of the 50S ribosomal subunit inhibiting protein synthesis | Mainly gram +ve activity |
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