Best Antibiotics for Group B Streptococcus (GBS) Infections
Penicillin G is the first-line antibiotic for treating Group B Streptococcus infections due to its narrow spectrum and effectiveness, with ampicillin being an acceptable alternative. 1
First-Line Treatment Options
For GBS During Pregnancy/Labor
- Penicillin G: 5 million units IV initial dose, followed by 2.5-3.0 million units IV every 4 hours until delivery 1
- Ampicillin: 2 g IV initial dose, then 1 g IV every 4 hours until delivery (acceptable alternative but less preferred due to broader spectrum) 1
For Non-Pregnant Adults with GBS Infections
- Penicillin G: First-line therapy for most GBS infections 2
- For necrotizing fasciitis caused by GBS: Penicillin plus clindamycin (600-900 mg/kg every 8 hours IV) 2
Alternatives for Penicillin-Allergic Patients
Mild Penicillin Allergy (no anaphylaxis history)
- Cefazolin: 2 g IV initial dose, then 1 g IV every 8 hours 1
Severe Penicillin Allergy (history of anaphylaxis)
- Clindamycin: 600-900 mg IV every 8 hours (if isolate is susceptible) 2, 1
- Vancomycin: 15-20 mg/kg IV every 8-12 hours (for resistant strains or when susceptibility unknown) 2, 3
Special Clinical Scenarios
GBS Bacteremia
- Remove infected catheters if present 1
- Obtain follow-up blood cultures to document clearance 1
- Consider combination therapy with gentamicin for severe infections, as this accelerates bacterial killing 4
GBS Skin and Soft Tissue Infections
- For mixed infections including GBS: Combination therapy may be needed
- Options include:
Important Considerations
Antibiotic Resistance Patterns
- GBS remains universally susceptible to penicillins and vancomycin 5, 6
- Resistance rates to other antibiotics:
Treatment Duration
- For invasive infections: Continue antibiotics until clinical improvement is evident and patient has been afebrile for 48-72 hours 2
- For GBS bacteremia: Treat until blood cultures are negative and source control is achieved 1
Pitfalls to Avoid
- Do not use oral antibiotics for GBS colonization during pregnancy - they are ineffective in eliminating carriage or preventing neonatal disease 2
- Do not rely solely on intramuscular penicillin for GBS eradication - studies show it's insufficient as sole therapy 7
- Do not automatically discontinue aminoglycosides when GBS infection is confirmed - combination therapy may provide more rapid killing 4
- Always check antibiotic susceptibility for non-penicillin options - resistance to clindamycin and erythromycin is significant 5, 6
By following these evidence-based recommendations, clinicians can optimize treatment outcomes for patients with GBS infections while minimizing the risk of antibiotic resistance.