What oral antibiotics cover Group B strep (Streptococcus agalactiae)?

Oral Antibiotics for Group B Streptococcus (Streptococcus agalactiae)

Penicillin and amoxicillin are the first-line oral antibiotics for treating Group B Streptococcus (GBS) infections, with clindamycin as the primary alternative for penicillin-allergic patients, provided susceptibility testing confirms effectiveness. 1

First-Line Oral Antibiotics

• Penicillin V: First choice due to its narrow spectrum of activity, which minimizes disruption to normal flora and reduces risk of developing antibiotic resistance 2

  • Adult dosing: 250 mg four times daily or 500 mg twice daily for 10 days
  • Pediatric dosing: 250 mg two to three times daily for 10 days

• Amoxicillin: Effective alternative to penicillin with similar efficacy 2

  • Adult dosing: 500 mg three times daily for 10 days
  • Pediatric dosing: 50 mg/kg once daily (maximum 1000 mg) or 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days

Alternatives for Penicillin-Allergic Patients

For Non-Anaphylactic Penicillin Allergy:

• Cefazolin (oral cephalosporin alternatives like cephalexin or cefuroxime may be used) 2
  • Note: About 10% of patients with penicillin allergy may also have hypersensitivity reactions to cephalosporins 2

For Anaphylactic Penicillin Allergy:

• Clindamycin: 300-450 mg orally three times daily for 10 days 3, 1

  • Important: Susceptibility testing is essential as resistance rates are increasing 4, 5
  • FDA-approved for treating infections caused by Streptococcus agalactiae (GBS) 1

• Azithromycin: 500 mg once daily for 5 days 3

  • Resistance rates are high (31% in some studies) 5
  • Should only be used when susceptibility is confirmed

• Vancomycin: Reserved for severe infections when other options aren't viable 2

  • Typically administered intravenously rather than orally

Antibiotic Resistance Considerations

• GBS remains largely susceptible to penicillins, though there have been reports of reduced susceptibility in some regions 4
• Resistance to second-line antibiotics is increasing:
  • Up to 31% resistance to azithromycin 5
  • Up to 19% resistance to clindamycin 5
• Susceptibility testing is crucial before using non-beta-lactam antibiotics 2, 4

Clinical Pearls and Pitfalls

• Pitfall: Oral antibiotics given before labor do not effectively eliminate GBS colonization and should not be used for this purpose 6
• Pitfall: Using broad-spectrum antibiotics unnecessarily can promote resistance development 4
• Pitfall: Assuming all GBS isolates are susceptible to clindamycin or erythromycin without testing 2, 5
• Pearl: A full 10-day course of antibiotics is essential for complete eradication, except for azithromycin which is given for 5 days due to its prolonged tissue persistence 3

Special Populations

• Pregnancy: For GBS prophylaxis during labor, intravenous antibiotics are preferred over oral options 7
• Renal Impairment: No dosage adjustment needed for clindamycin 1
• Elderly: Clindamycin elimination half-life increases to approximately 4 hours in elderly patients compared to 3.2 hours in younger adults, but dosage adjustment is not necessary with normal hepatic and age-adjusted renal function 1

Remember that antibiotic selection should be guided by susceptibility testing whenever possible, especially for non-penicillin options, as resistance patterns continue to evolve.