Updated: 2/28/2019

Penicillinase-Resistant Penicillins

Review Topic
  • A 55-year-old man presents to the emergency department with pain in his heel. His symptoms began a few days ago, when he developed heel pain that was unresponsive to acetaminophen and was associated with fever. He also endorses generalized malaise. Medical history is remarkable for diabetes complicated by peripheral neuropathy. Physical examination is notable for an erythematous and ulcerative lesion of the heal. A probe-to-bone test is positive. A bone biopsy is obtained and he is started on an empiric antibiotic. Cultures return positive for methicillin-sensitive Staphylococcus aureus and his antibiotics are narrowed to intravenous oxacillin. (Osteomyelitis)
  • Medications
    • oxacillin
    • nafcillin
    • dicloxacillin
  • 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
    • penicillinase-resistance
      • achieved by its bulky R group
  • Mechanism of resistance
    • altered penicillin-binding protein
      • thus methicillin-resistant Staphylococcus aureus (MRSA)
  • Clinical use
    • S. aureus (except MRSA)
  • Adverse effects
    • hypersensitivity reaction
    • interstitial nephritis

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