What antibiotics are recommended for Group B streptococcus (GBS) colonization in pregnant women?

Recommended Antibiotics for Group B Streptococcus in Pregnancy

For pregnant women colonized with Group B streptococcus (GBS), intravenous penicillin G is the first-line antibiotic for intrapartum prophylaxis, with specific alternatives for women with penicillin allergies based on their risk of anaphylaxis. 1

First-Line Antibiotic Regimens

Non-Allergic Patients

• Penicillin G: 5 million units IV initial dose, then 2.5-3.0 million units IV every 4 hours until delivery 1
  • Preferred due to narrow spectrum (less likely to select for resistant organisms)
• Alternative: Ampicillin, 2 g IV initial dose, then 1 g IV every 4 hours until delivery 1

Management of Penicillin-Allergic Patients

Low Risk for Anaphylaxis

• Cefazolin: 2 g IV initial dose, then 1 g IV every 8 hours until delivery 1
  • For patients without history of anaphylaxis, angioedema, respiratory distress, or urticaria following penicillin/cephalosporin administration

High Risk for Anaphylaxis

Patients with history of anaphylaxis, angioedema, respiratory distress, or urticaria following penicillin/cephalosporin administration:

1. If GBS isolate is susceptible to clindamycin and erythromycin:

   • Clindamycin: 900 mg IV every 8 hours until delivery 1

2. If GBS isolate is resistant to erythromycin but susceptible to clindamycin:

   • Clindamycin may be used only if testing for inducible clindamycin resistance is negative 1

3. If GBS isolate is resistant to clindamycin, shows inducible resistance, or susceptibility is unknown:

   • Vancomycin: 1 g IV every 12 hours until delivery 1

Important Clinical Considerations

Antimicrobial Susceptibility Testing

• For penicillin-allergic women at high risk for anaphylaxis, antimicrobial susceptibility testing of GBS isolates is essential 1
• Clinicians must specifically request this testing when submitting specimens 1

Key Changes from Previous Guidelines

• Erythromycin is no longer an acceptable alternative for GBS prophylaxis in penicillin-allergic women 1
• The definition of high risk for anaphylaxis has been clarified as history of anaphylaxis, angioedema, respiratory distress, or urticaria following administration of penicillin/cephalosporin 1

Timing of Antibiotic Administration

• Intrapartum antibiotic prophylaxis is optimal if administered for at least 4 hours before delivery 1
• Obstetric procedures should be timed accordingly when possible, but medically necessary procedures should not be delayed solely to achieve 4 hours of prophylaxis 1

Pitfalls to Avoid

• Do not use oral antibiotics to treat GBS colonization during pregnancy as this is ineffective in eliminating carriage or preventing neonatal disease 1
• Do not delay medically necessary obstetric procedures solely to achieve 4 hours of GBS prophylaxis 1
• Do not use erythromycin for GBS prophylaxis as it is no longer considered acceptable 1
• Do not administer vancomycin as first-line therapy; reserve it for penicillin-allergic women at high risk for anaphylaxis when clindamycin cannot be used 1
• Do not forget to request antimicrobial susceptibility testing when collecting specimens from penicillin-allergic patients 1

Special Considerations

• Vancomycin should be used with caution in patients with renal impairment and when administered with other potentially nephrotoxic drugs 2
• For women receiving antibiotics for suspected chorioamnionitis, additional GBS-specific prophylaxis is not needed if the regimen includes agents active against streptococci 1

By following these evidence-based recommendations, the risk of early-onset GBS disease in newborns can be significantly reduced while minimizing adverse effects of antibiotic therapy.