Penicillins

1. Natural Penicillins   (quick reference table)

• Examples: Penicillin G (IV,IM), Penicillin V po
• Spectrum:
  • Gram-positive: Effective against Streptococcus species, Enterococcus (limited)
  • Gram-negative: Limited (mainly Neisseria species)
  • Anaerobes: Limited anaerobic coverage
• Key Notes:
  • First-line treatment for syphilis.
  • No MSSA coverage.
  • Good for streptococcal infections.

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2. Aminopenicillins

• Examples: Ampicillin IV, Amoxicillin po
• Spectrum:
  • Gram-positive: Streptococcus, Enterococcus faecalis, Listeria
  • Gram-negative: Limited, covers some H. influenzae and E. coli
  • Anaerobes: Limited anaerobic activity
• Key Notes:
  • Listeria coverage makes it a drug of choice for Listeria infections.
  • Commonly used in respiratory and urinary tract infections.

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3. Anti-Staphylococcal Penicillins

• Examples: Nafcillin, Oxacillin
• Spectrum:
  • Gram-positive: Effective against MSSA, Streptococcus
  • Gram-negative: No coverage
  • Anaerobes: No coverage
• Key Notes:
  • First-line treatment for MSSA infections.
  • No activity against MRSA, Gram-negative, or anaerobes.

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4. Penicillins with β-lactamase Inhibitors

• Examples: Amoxicillin/Clavulanate (po Augmentin), Ampicillin/Sulbactam ( IV Unasyn)
• Spectrum:
  • Gram-positive: MSSA, Streptococcus, Enterococcus
  • Gram-negative: Extended coverage for H. influenzae, E. coli, Klebsiella, Acinetobacter (Sulbactam)
  • Anaerobes: Good anaerobic coverage
• Key Notes:
  • The β-lactamase inhibitors expand coverage to resistant Gram-negative and anaerobic organisms.
  • Used for mixed infections (e.g., respiratory, intra-abdominal).

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5. Anti-Pseudomonal Penicillins with β-lactamase Inhibitors

• Examples: Piperacillin/Tazobactam (Zosyn IV)
• Spectrum:
  • Gram-positive: MSSA, Streptococcus, Enterococcus
  • Gram-negative: Broad, including Pseudomonas, Enterobacteriaceae
  • Anaerobes: Good anaerobic coverage
• Key Notes:
  • Used in severe infections, especially where Pseudomonas and mixed infections are suspected.

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Summary

• Natural Penicillins: Great for Streptococcus, syphilis, but no MSSA coverage.
• Aminopenicillins: Broader Gram-positive coverage with Listeria activity, used in respiratory and urinary tract infections.
• Anti-Staphylococcal Penicillins: Best for severe MSSA infections but limited in other coverage.
• Penicillins with β-lactamase Inhibitors: Expands to MSSA, Gram-negative and anaerobic coverage, used in mixed infections.
• Anti-Pseudomonal Penicillins: Broad-spectrum, including Pseudomonas and anaerobic coverage, used in severe infections.