08/07/2025
Penicillins โ Brief Notes
Definition:
Penicillins are ฮฒ-lactam antibiotics originally derived from Penicillium mold. They are widely used to treat bacterial infections, especially those caused by Gram-positive organisms.
๐ฌ Mechanism of Action (General for Penicillins):
Penicillins inhibit bacterial cell wall synthesis.
They bind to Penicillin-Binding Proteins (PBPs) (especially transpeptidase).
This blocks peptidoglycan cross-linking, weakening the cell wall.
Leads to cell lysis and death (bactericidal effect).
๐ Categories of Penicillins & Their Mechanism of Action
Category Examples Mechanism of Action Coverage
1. Natural Penicillins Penicillin G (IV), Penicillin V (oral) Bind to PBPs โ inhibit peptidoglycan synthesis โ cell wall disruption Gram-positive cocci (Strep), Gram-negative cocci (Neisseria), Treponema pallidum (syphilis)
2. Penicillinase-Resistant Penicillins (Anti-staphylococcal) Methicillin (not used clinically), Oxacillin, Cloxacillin, Dicloxacillin Same as above, but resistant to ฮฒ-lactamase (penicillinase) enzyme Used for ฮฒ-lactamase-producing Staphylococcus aureus (non-MRSA)
3. Aminopenicillins (Extended-spectrum) Amoxicillin, Ampicillin Same as above, but broader spectrum due to better pe*******on into Gram-negative bacteria Gram-positive + some Gram-negatives (E. coli, H. influenzae)
4. Extended-Spectrum Penicillins (Anti-pseudomonal) Piperacillin, Ticarcillin Same basic mechanism, also effective against Pseudomonas and other resistant Gram-negative rods Gram-positive + strong Gram-negative including Pseudomonas
5. Penicillins + ฮฒ-lactamase Inhibitors Amoxicillin + Clavulanic acid, Piperacillin + Tazobactam Clavulanate or tazobactam inhibit ฮฒ-lactamase, allowing penicillin to act effectively Broad spectrum, including ฮฒ-lactamase producing organisms
๐ Clinical Uses:
Penicillin G/V: Strep infections, syphilis
Oxacillin/Cloxacillin: Staph infections (MSSA)
Amoxicillin: Ear infections, sinusitis, bronchitis
Ampicil
