Penicillin group

Types of penicillins

• Narrow spectrum penicillins
  * Benzylpencillin (Penicillin G)
  * Phenoxymethylpencillin (Penicillin V)
  * Benzathine penicillin
  * Procaine penicillin
• Narrow spectrum penicillins resistant to staphylococcal beta-lactamase (flucloxacillin)
  * Dicloxacillin
  * Flucloxacillin
• Moderate spectrum penicillins
  * Amoxycillin
  * Ampicillin
• Broad spectrum penicillin
  * Amoxycillin with clavulanic acid
• Broad spectrum penicillins with anti-pseudomonal activities
  * Piperacillin
  * Piperacillin with tazobactam
  * Ticarcillin with clavulanic acid

Group characteristics

• All have fused beta-lactam/thiazolidine ring
• Side chains determine antibacterial, pharmacological, and pharmacokinetic properties

Actions

Bactericidal, by interfere with bacterial cell wall (peptidoglycan) synthesis

Mechanism of action

Intact beta-lactam ring binds to various proteins
--> Binds to transpeptidase and carboxypeptidase
--> Prevents cross-linkage of peptidoglycan
--> Bacterial cell wall weakened

Antibacterial spectrum

Gram-positive cocci has thick peptidoglycan cell wall

When exposed to beta-lactam
--> Growth continue at normal rate (but with reduced cross-linkage)
--> Cell wall becomes weakened
--> Lysis

Release of bacterial cellular component (lipoteichoic acid, a bacterial sugar alcohol phosphate)
--> Accelerate peptidoglycan breakdown
--> Cell death

Rarely results in bacterial killing to the point of extinction

Some sensitive cells (the persistors) will remain dormant until the antibiotic is removed

Extinction is achieved by the addition of a synergistic antibiotics, e.g. aminoglycoside
* Gentamicin can penetrate the cell walls better due to peptidoglycan damage

Gram-negative bacilli