What antibiotics cover Streptococcus agalactiae (Group B strep) in patients allergic to Penicillin (PCN)?

Antibiotic Options for Group B Streptococcus in Penicillin-Allergic Patients

For patients with penicillin allergy, cefazolin is the preferred antibiotic for Group B Streptococcus (GBS) coverage if the patient is not at high risk for anaphylaxis, while vancomycin should be used for those at high risk for anaphylaxis when susceptibility testing is unavailable or shows resistance to clindamycin. 1

Antibiotic Selection Algorithm Based on Penicillin Allergy Risk

Low Risk for Anaphylaxis

Patients with penicillin allergy but without history of:

• Anaphylaxis
• Angioedema
• Respiratory distress
• Urticaria following penicillin or cephalosporin administration

Recommended Treatment:

• Cefazolin 2g IV initial dose, then 1g IV every 8 hours until delivery 1
  • Cefazolin achieves effective intraamniotic concentrations
  • GBS isolates remain highly susceptible to cefazolin
  • Cross-reactivity between penicillins and cephalosporins occurs in only about 10% of patients 1

High Risk for Anaphylaxis

Patients with penicillin allergy with history of:

• Anaphylaxis
• Angioedema
• Respiratory distress
• Urticaria following penicillin or cephalosporin administration

Recommended Treatment:

1. If GBS isolate susceptibility testing is available:

   • Use clindamycin 900mg IV every 8 hours if the isolate is:
     • Susceptible to clindamycin AND
     • Either susceptible to erythromycin OR
     • If resistant to erythromycin, testing for inducible clindamycin resistance is negative 1

2. Use vancomycin 1g IV every 12 hours until delivery if:

   • Susceptibility testing is not available
   • GBS isolate is resistant to clindamycin
   • GBS isolate shows inducible resistance to clindamycin 1

Important Considerations

Rising Antibiotic Resistance

• Clindamycin resistance rates range from 17.2% to 28% in recent studies 2, 3
• Erythromycin resistance rates range from 21.1% to 32.9% 2, 4
• Resistance to erythromycin is frequently associated with clindamycin resistance (92% co-resistance in some studies) 2
• All GBS isolates remain susceptible to penicillin, ampicillin, and vancomycin 3, 5

Susceptibility Testing

• Susceptibility testing should be performed on prenatal GBS isolates from penicillin-allergic women at high risk for anaphylaxis 1
• Testing for inducible clindamycin resistance (D-zone test) is crucial when considering clindamycin for treatment 1

Common Pitfalls to Avoid

1. Never use erythromycin for GBS prophylaxis - it is no longer recommended due to high resistance rates 1
2. Don't use clindamycin empirically without susceptibility testing - approximately 20% of GBS isolates are resistant 6
3. Don't assume clindamycin susceptibility based on erythromycin susceptibility - inducible resistance may be present 1
4. Don't use cephalosporins in patients with high risk for anaphylaxis to penicillin due to potential cross-reactivity 1

Special Situations

Chorioamnionitis

• For penicillin-allergic patients with chorioamnionitis, broader spectrum agents may be necessary 6
• Consider adding gentamicin for gram-negative coverage in addition to GBS-active agents 6

Neonatal Implications

• Neonates born to mothers with inadequate GBS prophylaxis may require additional monitoring or empiric treatment 1
• Limited evaluation including blood culture and CBC with differential may be indicated 1

By following this algorithm, clinicians can provide effective coverage against Group B Streptococcus while minimizing risk in penicillin-allergic patients.