USMLE

Cephalosporins Overview

1,926 views
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

Cephalosporins are a class of antibiotics ‘used to treat a variety of bacterial infections. Like penicillins, these drugs are beta-lactam antibiotics; they are D-Ala-D-Ala analogs that bind to and block the bacterial transpeptidase, thereby preventing the cross-linking of the bacterial cell wall. Cephalosporins are also resistant to penicillinase, a bacterial enzyme that can deactivate penicillins by cleaving the beta-lactam ring. Because of this, many cephalosporins can be used to treat penicillin-resistant bacteria. However, cephalosporins also have a host of their own side effects. Firstly, patients may develop an allergic reaction after taking cephalosporins, which usually manifests as a rash. Taking cephalosporins can also lead to creation of auto-antibodies that cause hemolytic anemia. Finally, a disulfiram-like reaction to alcohol and vitamin K deficiency are important side effects seen with taking cephalosporins. 

Key Points

  • Cephalosporins
    • Mechanism
      • Beta-lactam antibiotics
        • Works in a similar fashion to penicillin to bind to penicillin-binding proteins (transpeptidases) and prevent cell wall cross-linking
          • In penicillins, beta-lactam is bonded to a penam (thiazolidine) ring, and a side chain
          • In cephalosporins, beta-lactam is bonded to a cepham dihydrothiazine ring
      • Bactericidal
    • Clinical Use
      • Different bacterial coverage dependent on generation of drug
    • Adverse Effects
      • Hypersensitivity (allergy)
        • Most commonly seen with cefazolin administered pre-op
        • Low rate of cross-allergenicity with penicillin-allergic patients
      • Autoimmune hemolytic anemia
      • Disulfiram-like reaction to alcohol
      • Vitamin K deficiency
        • May cause bleeding
      • Increases nephrotoxicity of aminoglycosides
    • Resistance
      • Resistant to penicillinase (beta-lactamase)
        • Esp. later generation (e.g. 3rd generation), explains why they have more gram-negative activity
      • Resistance develops by
        • Structural change in penicillin-binding proteins (transpeptidases)
        • Production of cephalosporinases