Benzylpenicillin (Pen G)

• Intrapartum GBS prophylaxis
• Maternal sepsis (with broader cover)
• Congenital syphilis prevention (benzathine form)

Binds penicillin-binding proteins → inhibits peptidoglycan cross-linking → bactericidal.

• 3 g IV loading
• 1.5 g IV q4h until delivery
• Target ≥4 h before birth for full effect

GBS prophylaxis

3 g IV loading, then 1.5 g q4h until birth

Penicillin allergy (low risk)

Cefazolin 2 g IV → 1 g q8h

Severe penicillin allergy

Vancomycin 20 mg/kg IV q8h

• AbsolutePrevious anaphylaxis to penicillins

• Rash, anaphylaxis
• Jarisch-Herxheimer (syphilis)
• C. difficile (rare)

• • Safe across pregnancy & lactation.
• • Crosses placenta — therapeutic fetal levels achieved.

• Methotrexate

  Caution

  ↑ MTX toxicity

• 💡 Always document allergy details — many "penicillin allergies" are intolerance.
• 💡 GBS prophylaxis effective from 4 h before delivery.