What oral antibiotics are used to treat group B strep (Streptococcus agalactiae)?

Oral Antibiotics for Group B Streptococcus (Streptococcus agalactiae) Treatment

For Group B Streptococcus (GBS) infections, penicillin and ampicillin remain the first-line oral antibiotic treatments, with clindamycin being the preferred alternative for penicillin-allergic patients due to high rates of erythromycin resistance.

First-Line Treatment Options

• Penicillin V: The gold standard oral treatment for GBS infections

  • Dosage: 500 mg 2-3 times daily for adults
  • Duration: 10 days

• Amoxicillin: An effective alternative to penicillin V

  • Dosage: 500 mg three times daily for adults
  • Duration: 10 days

Both penicillin and ampicillin demonstrate universal susceptibility against GBS, supporting their continued use as first-line agents 1, 2.

Alternative Options for Penicillin-Allergic Patients

For patients with penicillin allergy, treatment options depend on the severity of the allergy:

Non-severe Penicillin Allergy (no anaphylaxis, angioedema, or respiratory distress)

• Cephalexin (first-generation cephalosporin)
  • Dosage: 500 mg four times daily
  • Duration: 10 days
  • Note: Approximately 10% cross-reactivity with penicillin allergy 3

Severe Penicillin Allergy

• Clindamycin

  • Dosage: 300 mg three times daily
  • Duration: 10 days
  • Indicated for treatment of serious infections due to susceptible strains of streptococci 4
  • Resistance rates around 4-15%, which is significantly lower than erythromycin 1, 2

• Vancomycin (typically reserved for severe infections or when other options aren't suitable)

  • Used when GBS is resistant to clindamycin or in severe infections

Antibiotics to Avoid or Use with Caution

• Erythromycin: Not recommended as first-line alternative due to high resistance rates

  • Resistance rates have increased from 15.8% to 32.8% 2
  • Studies show resistance rates of 21-25% 1, 5

• Azithromycin: Similar concerns as erythromycin

  • Resistance rates around 32% 5
  • Only indicated for GBS in specific situations per FDA labeling 6

Important Clinical Considerations

1. Susceptibility Testing:

   • For penicillin-allergic patients, susceptibility testing should be performed before prescribing clindamycin or erythromycin due to increasing resistance 1, 2

2. Regional Variations:

   • Antibiotic resistance patterns vary by geographic region 7
   • Local antibiotic resistance patterns should guide therapy for non-penicillin options

3. Risk of C. difficile:

   • Clindamycin carries a higher risk of Clostridioides difficile infection compared to other antibiotics 4
   • This risk should be considered, especially in vulnerable patients

4. Complete Treatment Course:

   • Patients should complete the full course of antibiotics even if symptoms improve quickly to prevent recurrence and resistance development

Special Situations

Pregnant Women with GBS

• Intravenous antibiotics during labor are the standard for preventing neonatal GBS disease
• Screening is recommended between 36 0/7 and 37 6/7 weeks' gestation 8
• Oral antibiotics are not recommended for GBS colonization during pregnancy as they don't prevent neonatal transmission

Invasive GBS Infections

• Typically require intravenous antibiotics initially
• May transition to oral therapy for completion after clinical improvement
• All invasive GBS strains remain susceptible to penicillin, ampicillin, and cefotaxime 7

Remember that while oral antibiotics may be appropriate for mild to moderate GBS infections, severe or invasive infections typically require initial intravenous therapy before transitioning to oral options.