Penicillinase-Sensitive vs. Penicillinase-Resistant Penicillins

Summary

Penicillinase-sensitive penicillins or PSPs, and Penicillinase-Resistant Penicillins, or PRPs, are both groups of beta-lactam antibiotics in the penicillin family.

Penicillinase-sensitive penicillins, as their name suggests, are penicillins sensitive to cleavage by beta-lactamases, and important drugs of this group include Amoxicillin and Ampicillin. The PSPs have broad-spectrum coverage of both gram-positive and gram-negative organisms and are often combined with beta-lactamase inhibitors to offset their susceptibility to cleavage and inactivation..

Penicillinase-Resistant Penicillins include Nafcillin, Methicillin, and Oxacillin. Since these drugs have bulky chemical structures that block access to their beta-lactam rings, they are resistant to cleavage by penicillinase enzymes. PRPs provide narrow spectrum coverage and are primarily used to treat infections by Staph aureus.

Key Points

• Penicillinase-resistant Penicillins
  • Drug Names
    • Nafcillin
    • Methicillin
    • Oxacillin
    • Dicloxacillin
  • Mechanism
    • Same as Penicillin
  • Clinical Use
    • Narrow-spectrum coverage
      • Usually used for S. aureus (except MRSA)
  • Adverse Effects
    • Same as Penicillin
  • Resistance
    • Resistant to penicillinase (beta-lactamase)
      • This is obvious by the class name
      • Bulky R-group blocks access of beta-lactamase to beta-lactam ring
    • Altered penicillin-binding protein
      • e.g. MRSA
  • Penicillinase-Sensitive Penicillins
    • Also known as the aminopenicillins
    • Drug Names
      • Amoxicillin
        • Has greater oral availability
      • Ampicillin
    • Mechanism
      • Same as Penicillin
    • Clinical Use
      • Broader-spectrum coverage against gram-negative species
        • H. influenzae
        • H. pylori
        • E. Coli
        • Listeria monocytogenes
        • Proteus mirabilis
        • Salmonella
        • Shigella
        • Enterococci
    • Adverse Effects
      • Same as Penicillin
    • Resistance
      • Sensitive to penicillinase (beta-lactamase)
        • Obvious by class name
        • Enzymes produced by bacteria that cleave beta-lactam ring
        • May be administered with beta-lactamase inhibitors (e.g. clavulanic acid, sulbactam, tazobactam) to prevent breakdown