USMLE

Penicillinase-Sensitive vs. Penicillinase-Resistant Penicillins

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Antibiotics / Antiparasitics
  1. Penicillin Overview
  2. Penicillinase-Sensitive vs. Penicillinase-Resistant Penicillins
  3. Anti-Pseudomonal Penicillins
  4. Cephalosporins Overview
  5. 1st Generation Cephalosporins
  6. 2nd Generation Cephalosporins
  7. 3rd Generation Cephalosporins
  8. 4th Generation Cephalosporins
  9. 5th Generation Cephalosporins
  10. Carbapenems
  11. Monobactams (Aztreonam)
  12. Vancomycin
  13. Aminoglycosides
  14. Tetracyclines
  15. Tigecycline
  16. Chloramphenicol
  17. Clindamycin
  18. Linezolid
  19. Macrolides
  20. Polymyxins
  21. Sulfonamides
  22. Dapsone
  23. Trimethoprim
  24. Fluoroquinolones
  25. Daptomycin
  26. Metronidazole
  27. Rifamycins (Rifampin, Rifabutin)
  28. Isoniazid
  29. Pyrazinamide
  30. Ethambutol
  31. Chloroquine

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