What antibiotic is prescribed for a patient with Group B streptococcus (GBS) beta-hemolytic infection who has an allergy to penicillin?

Antibiotic Treatment for Group B Streptococcus in Penicillin-Allergic Patients

For patients with Group B streptococcus (GBS) infection who are allergic to penicillin, cefazolin is the recommended first-line alternative for those without history of anaphylaxis, while clindamycin (if susceptible) or vancomycin should be used for those with high risk of anaphylaxis. 1

Antibiotic Selection Algorithm Based on Allergy History

1. Assess Penicillin Allergy Severity

• Low risk for anaphylaxis: History without anaphylaxis, angioedema, respiratory distress, or urticaria
• High risk for anaphylaxis: History of anaphylaxis, angioedema, respiratory distress, or urticaria following penicillin or cephalosporin administration

2. Antibiotic Selection

For Patients with Low Risk of Anaphylaxis:

• First choice: Cefazolin 1, 2
  • Dosage: 2 g IV initial dose, then 1 g IV every 8 hours until delivery (for pregnant women) 2
  • For non-pregnant adults with GBS infection: 1-2 g IV every 8 hours 2

For Patients with High Risk of Anaphylaxis:

• Perform antimicrobial susceptibility testing on the GBS isolate 1
• If susceptible to clindamycin and erythromycin: Use clindamycin
  • Clindamycin is preferred over erythromycin due to lower resistance rates 3, 4
• If resistant to erythromycin but susceptible to clindamycin: Use clindamycin only if testing for inducible clindamycin resistance is negative 1
• If resistant to clindamycin or susceptibility unknown: Use vancomycin 1, 2

Important Considerations

Resistance Patterns

• GBS remains universally susceptible to penicillin and cephalosporins 4
• Resistance to clindamycin has been reported in 3-15% of isolates 1, 3, 4
• Resistance to erythromycin is higher (7-25%) 1, 3
• Erythromycin is no longer an acceptable alternative for intrapartum GBS prophylaxis 1

Susceptibility Testing

• Antimicrobial susceptibility testing should be performed on all GBS isolates from penicillin-allergic patients at high risk for anaphylaxis 1, 5
• Testing should include assessment for inducible clindamycin resistance using the D-zone test for isolates that are erythromycin-resistant but clindamycin-susceptible 1

Special Populations

• For pregnant women requiring intrapartum prophylaxis, the same principles apply, with specific dosing regimens for labor and delivery 1, 2
• For urinary tract infections caused by GBS in penicillin-allergic patients, oral options include cephalexin (for non-severe allergy) or fluoroquinolones (if susceptible) 2

Common Pitfalls to Avoid

1. Failing to verify penicillin allergy history - Many reported penicillin allergies are not true allergies
2. Not performing susceptibility testing - Essential for high-risk anaphylaxis patients to guide appropriate antibiotic selection
3. Using erythromycin - No longer recommended due to high resistance rates
4. Not testing for inducible clindamycin resistance - Critical when considering clindamycin in erythromycin-resistant isolates
5. Unnecessary use of vancomycin - Should be reserved for cases where clindamycin cannot be used due to resistance or unknown susceptibility

By following this evidence-based approach to antibiotic selection for GBS infections in penicillin-allergic patients, clinicians can provide effective treatment while minimizing the risk of allergic reactions and antimicrobial resistance.