Antibiotic mechanisms of action Flashcards
Penicillins
Examples, mechanism
End in -cillin
- Intact beta-lactam ring is essential for activity
- **Time-dependent bacteriacidal action **
- Affect cell wall synthesis by binding to active serine site on penicillin binding protein -> irreversible de-activation of transpeptidase enzyme responsible for forming peptidoglycan cross-links.
Cephalosporins
Examples, mechanism
Ceflaclor (first gen), cefuroxime (2nd gen), cefotaxime, ceftriaxone (3rd gen), cefepime, cefpirome (4th gen), ceftaroline, ceftobripole (5th gen)
Beta-lactam ring is fused with a dihydrothiazine ring to produce the cephem nucleus
Bacteriacidal
Affect cell wall synthesis by disrupting peptidoglycan cell wall integrity
Carbapenems
Examples, mechanism
Imipenem, meropenem, ertapenem
- Beta-lactam.
- Due to subtle modification of beta-lactam ring some groups are changed and ring is fused - significant resistant to most beta-lactamases.
- Bactericidal - disrupt cell wall synthesis
Glycopeptides
Examples, structure, mechanism
Vancomycin, teicoplanin, semi-synthetic analogues (2nd gen): dalbavancin, telavancin
- Glycosylated non-ribosomal heptapeptides that do not contain a beta-lactam ring
- Time-dependent bactericidal action.
- Inhibit cell wall synthesis by binding to subunits of the peptidoglycan: preventing addition of new molecules and cell wall synthesis. Similar mechanism to beta-lactams but no competition between peniciilins and glycopeptides for the active binding site.
Aminoglycosides
Examples, structure, mechanism
Gentamicin, amikacin, neomycin, streptomycin, tobramycin
- **Concentration-dependent bactericidal **
- Inhibit protein synthesis by binding irreversibly to bacterial 30S ribosomal subunit.
Chloramphenicol
Family, mechanism
An amphenicol
- Bacteriostatic
- Inhibits protein synthesis.
- Binds to residues of the 50S ribosomal subinit by preventing peptide bond formation and subsequent protein synthesis.
Tetracyclines
Examples, structure, mechanism
Doxycycline, tetracycline, lymecycline, tigecycline, demeclocycline
- Lienar fused tetracyclic nucleus with differing side chains
- Bacteriostatic
- Inhibit protein synthesis
Macrolides
Examples, structure, mechanism
Erythryomycin, clarithromycin, azithromycin
- Lactone ring at centre
- Bacteriostatic (may be bacteriocidal depending on concentration and bacterial species)
- Inhibit protein synthesis
Clindamycin
Family, mechanism
A licosamide.
- Inhibits protein synthesis
- May be bacteriostatic or bactericidal
Linezolid
Family, mechanism
A oxazololidinone, also tedizolid
- Inhibits protein synthesis
- Bacteriostatic vs enterococci and staphylococci
- Bactericidal vs streptococci
Metronidazole
Family, mechanism
Nitroimidazole (also tinidazole)
- Concentration-dependent bactericidal action
- Inhibits normal nucleic acid replication
Co-trimoxazole
Sulfamethoxazole (sulphonamide) + trimethoprim
- Sulfamethoxazole alone is bacteriostatic
- Co-trimoxazole is bacteriocidal and inhibits normal nucleic acid replication
Fluoroquinolones
Examples, mechanism
Ciprofloxacin, moxifloxacin
- Concentration dependent bactericidal action
- Inhibit normal nucleic acid replication
Rifampicin
Family, mechanism
A rifamycin (also rifabutin, rifamixin)
- Bacteriacidal
- Inhibit normal nucleic acid replication
Time-dependent bactericidal action
Mechanism, dosing, post antibiotic effects, examples (3)
- Slow bactericidal drugs, need drug concentration to be >MIC for at least 50% of the dosing interval. Magnitude of concentration above MIC has little relevance (more killing does not occur at higher concentrations)
- Minimum bactericidal concentration similar to minimum inhibitory concentration
- Often given in multiple daily doses, Amenable to continuous infusions following loading dose: aim to keep trough serum levels of free drug >MIC. Larger doses work by increasing duration of time drug concentration is above MIC
- Minimal post-antibiotic effects.
Penicillins, vancomycin, teicoplanin
