What antibiotics cover Streptococcus agalactiae?

Antibiotics for Streptococcus agalactiae (Group B Streptococcus)

Penicillin G is the first-line antibiotic for treating Streptococcus agalactiae infections due to its narrow spectrum of activity, proven efficacy, and the fact that no resistance has been documented. 1

First-line Treatment Options

For Non-Allergic Patients:

• Penicillin G: 5 million units IV initial dose, then 2.5 million units IV every 4 hours until delivery/resolution (for intrapartum prophylaxis or treatment) 2
• Ampicillin: 2 g IV initial dose, then 1 g IV every 4 hours (alternative to penicillin) 2
• Amoxicillin: 500 mg orally three times daily for 10 days (for less severe infections) 3

For Penicillin-Allergic Patients:

• Non-anaphylactic allergy:

  • Cefazolin: 2 g IV initial dose, then 1 g IV every 8 hours 2

• Anaphylactic allergy (with susceptibility testing available):

  • Clindamycin: 900 mg IV every 8 hours 2, 4
  • Erythromycin: 500 mg IV every 6 hours 2

• Anaphylactic allergy (without susceptibility testing or resistant strains):

  • Vancomycin: 1 g IV every 12 hours 2
  • Linezolid: 600 mg IV/PO twice daily 2

Antimicrobial Resistance Considerations

It's important to note that while S. agalactiae remains universally susceptible to penicillin and other β-lactams, resistance to alternative antibiotics is increasing:

• Recent studies show high resistance rates to erythromycin (29-46%) and clindamycin (47-63%) 5
• A 2023 study from China found that all tested S. agalactiae strains remained susceptible to penicillin, ampicillin, linezolid, vancomycin, tigecycline, and quinupristin-dalfopristin 6

Clinical Scenarios

Invasive Infections (Meningitis, Endocarditis)

For severe invasive infections like meningitis or endocarditis:

• First-line: Penicillin G at high doses 1
• Alternative: Vancomycin 15-20 mg/kg/dose IV every 8-12 hours 2
• Some experts recommend adding rifampin to vancomycin for meningitis cases 2

Intrapartum Prophylaxis

For preventing neonatal GBS disease:

• First-line: Penicillin G 5 million units IV initial dose, then 2.5 million units IV every 4 hours until delivery 2
• Alternative: Ampicillin 2 g IV initial dose, then 1 g IV every 4 hours until delivery 2

Eradication of Carriage

For eradicating GBS colonization in healthcare workers or high-risk individuals:

• Oral penicillin: 500 mg four times daily for 10 days 2
• Amoxicillin: 500 mg three times daily for 10 days 2
• Clindamycin: 300-500 mg four times daily for 10 days 2
• Azithromycin: 500 mg once daily for 3-5 days 2

Important Clinical Pearls

1. Universal susceptibility: S. agalactiae remains universally susceptible to penicillin, making it the drug of choice for all infections 6

2. Resistance testing: For penicillin-allergic patients, susceptibility testing for clindamycin and erythromycin should be performed when possible due to increasing resistance rates 2, 5

3. Combination therapy: For severe invasive infections like meningitis, some experts recommend combination therapy (e.g., vancomycin plus rifampin) 2

4. Duration of therapy: Treatment duration should be based on clinical response and infection site:

   • Uncomplicated infections: 7-14 days
   • Invasive infections (meningitis, endocarditis): 2-4 weeks

5. Common pitfall: Relying on erythromycin or clindamycin empirically without susceptibility testing in penicillin-allergic patients may lead to treatment failure due to increasing resistance rates 5