What are the alternative antibiotics for Group B strep (Group B streptococcus) prophylaxis in patients allergic to penicillin?

Alternative Antibiotics for Group B Streptococcus in Penicillin-Allergic Patients

For patients allergic to penicillin, the recommended alternative antibiotics for Group B streptococcus (GBS) prophylaxis depend on the severity of the allergic reaction, with cefazolin being preferred for non-severe allergies and vancomycin or clindamycin (if susceptible) for severe allergies. 1

Assessment of Penicillin Allergy Severity

• Determine if the patient has a high risk for anaphylaxis, defined as a history of anaphylaxis, angioedema, respiratory distress, or urticaria following administration of penicillin or cephalosporin 1
• For patients without these severe reactions, cefazolin is the recommended alternative, as true penicillin allergy occurs in a smaller percentage of patients than reported 2, 3
• Approximately 10% of persons with penicillin allergy have cross-reactivity with cephalosporins, making allergy history verification important 3

Treatment Algorithm Based on Allergy Severity

For Non-Severe Penicillin Allergy:

• Cefazolin: 2g IV initial dose, then 1g IV every 8 hours until delivery 1
• Cefazolin is preferred because pharmacologic data suggest it achieves effective intraamniotic concentrations 1
• GBS isolates remain highly susceptible to cefazolin, with minimum inhibitory concentrations consistently low 3, 4

For Severe Penicillin Allergy (history of anaphylaxis, angioedema, respiratory distress, or urticaria):

• Obtain antimicrobial susceptibility testing for clindamycin and erythromycin if possible 1
• If the isolate is susceptible to clindamycin:
  • Clindamycin: 900 mg IV every 8 hours until delivery 1
• If susceptibility testing is not performed, results are not available, or isolate is resistant:
  • Vancomycin: 1g IV every 12 hours until delivery 1

Important Considerations

• Resistance to erythromycin (21%) is more common than resistance to clindamycin (4%), making clindamycin generally preferred when susceptible 4
• If an isolate is resistant to erythromycin but susceptible to clindamycin, testing for inducible clindamycin resistance should be performed 1
• Erythromycin is no longer recommended for GBS infections due to increasing resistance 2, 5
• All GBS isolates remain susceptible to penicillin worldwide, making it the first choice when not contraindicated 2
• Vancomycin should be reserved for cases where no other options exist, due to concerns about promoting antimicrobial resistance 3

Clinical Pearls and Pitfalls

• Always obtain susceptibility testing when treating GBS infections in penicillin-allergic patients 2, 3
• The CDC recommends against using cefazolin in patients with severe penicillin allergy due to risk of cross-reactivity 2
• Consider penicillin allergy testing during pregnancy, as confirmation or delabeling from a penicillin allergy can provide both short- and long-term health benefits 6
• A recent study found that antibiotic susceptibility testing was performed on GBS isolates in only 74.2% of penicillin-allergic patients, indicating room for improvement in following guidelines 7
• Intrapartum antibiotic prophylaxis is optimal if administered for at least 4 hours before delivery 1