Cephalosporins

Cephalosporins - Wall-Wrecking Wonders

• Identity: Bactericidal β-lactam antibiotics, structural analogs of D-Ala-D-Ala.
• Mechanism: Inhibit cell wall synthesis by covalently binding to Penicillin-Binding Proteins (PBPs).
• Action: This binding blocks the transpeptidation reaction, preventing peptidoglycan cross-linking. The result is a weakened cell wall, leading to osmotic lysis and cell death. 📌 Cephalosporins Clobber Cell wall Synthesis.

⭐ Cephalosporins are structurally similar to penicillins but are generally more resistant to bacterial β-lactamases, which often contributes to a broader spectrum of activity against various pathogens.

The Generations - A Spectrum Story

Spectrum shifts from primarily Gram-positive to broad Gram-negative coverage with each successive generation.

• 1st Gen (e.g., Cefazolin, Cephalexin):
  • Excellent Gram-positive (Staph/Strep) coverage. PEcK: Proteus, E. coli, Klebsiella.
  • Minimal Gram-negative activity.
• 2nd Gen (e.g., Cefoxitin, Cefuroxime):
  • Retains Gram-positive activity; adds more Gram-negative coverage. HEN-PEcK: H. influenzae, Enterobacter, Neisseria.
• 3rd Gen (e.g., Ceftriaxone, Ceftazidime):
  • Broad Gram-negative coverage. Some lose potent Gram-positive activity.
  • Ceftazidime covers Pseudomonas.
• 4th Gen (e.g., Cefepime):
  • Broadest spectrum; strong Gram-positive and Gram-negative activity, including Pseudomonas.
• 5th Gen (e.g., Ceftaroline):
  • Similar to 3rd Gen but uniquely covers MRSA.

⭐ While Gram-negative coverage increases with generation, 1st generation agents like Cefazolin remain superior for methicillin-sensitive Staphylococcus aureus (MSSA).

📌 LAME: Organisms not covered by most cephalosporins: Listeria, Atypicals (Chlamydia, Mycoplasma), MRSA (except Ceftaroline), and Enterococci.

Clinical Action - Hits and Hazards

Clinical Uses (Hits)

• Surgical prophylaxis: Cefazolin (1st gen)
• Meningitis & Community-Acquired Pneumonia (CAP): Ceftriaxone (3rd gen)
• Gonorrhea: Ceftriaxone (3rd gen)

Adverse Effects (Hazards)

• Hypersensitivity: Cross-reactivity with penicillin is low (<10%).
• ⚠️ Disulfiram-like reaction: With alcohol. (e.g., Cefotetan).
  • 📌 Mnemonic: "Don't drink Te-quila with Cefotetan".
• Bleeding: Can cause vitamin K deficiency.
• Biliary sludging: With Ceftriaxone.

⭐ Exam Favorite: Ceftriaxone is mainly eliminated via bile, making it useful in renal failure. However, it's contraindicated in neonates due to the risk of biliary sludging and kernicterus.

High‑Yield Points - ⚡ Biggest Takeaways

• All are β-lactam antibiotics that inhibit cell wall synthesis; generally ineffective against LAME organisms (Listeria, Atypicals, MRSA, Enterococci).
• 1st-gen (e.g., Cefazolin) are workhorses for surgical prophylaxis.
• 3rd-gen (e.g., Ceftriaxone, Cefotaxime) achieve good CNS penetration, making them key for treating meningitis.
• Ceftriaxone is unique for its biliary excretion.
• 4th-gen (Cefepime) provides broad-spectrum coverage, including Pseudomonas aeruginosa.
• 5th-gen (Ceftaroline) is the only one with activity against MRSA.