Penicillin

Snapshot

• A 25-year-old man presents to his primary care physician for a penile lesion that he noticed earlier in the day. He reports that the lesion is not associated with pain, and he endorses to being sexually active with multiple women without the use of barrier contraception. Physical examination is notable for an indurated and painless lesion on the penis with superficial ulcerations. He also has local adenopathy. A fluorescent treponemal antibody absorption and rapid plasma reagin test are positive. He is started on benzathine penicillin G. (Primary syphilis)

Introduction

• Mechanism of action
  • impairs bacterial cell wall synthesis
    • penicillin is a D-Ala-D-Ala analog that binds to penicillin-binding proteins (transpeptidases), impairing peptidoglycan cross-linking  
• Mechanism of resistance
  • altered penicillin-binding proteins
  • production of β-lactamases
    • penicillin has a β-lactam ring
• Clinical use
  • gram-positive cocci
    • except for penicillinase-producing staphylococci, penicillin-resistant pneumococci, enterococci, and oxacillin-resistant staphylococci)
  • Listeria
  • Neisseria spp.
    • except for penicillinase-producing Neisseria
  • most anaerobes
    • with certain important exceptions, including Bacteroides
• Adverse reactions
  • direct Coombs-positive hemolytic anemia
  • drug-induced interstitial nephritis
  • hypersensitivity reactions