What is the recommended treatment for Group B Streptococcus (GBS) bacteriuria in pregnancy for a patient allergic to amoxicillin?

Treatment for Group B Streptococcus Bacteriuria in Pregnancy with Amoxicillin Allergy

For pregnant women with GBS bacteriuria who are allergic to amoxicillin, cefazolin is the recommended first-line treatment if the patient is not at high risk for anaphylaxis, while clindamycin (if the isolate is susceptible) or vancomycin (if susceptibility is unknown or shows resistance) should be used in patients with high risk for anaphylaxis.

Assessment of Penicillin Allergy

Before selecting an antibiotic regimen, it's crucial to assess the severity of the penicillin allergy:

• Low risk for anaphylaxis: Patients without history of anaphylaxis, angioedema, respiratory distress, or urticaria following administration of penicillin or cephalosporin
• High risk for anaphylaxis: Patients with history of anaphylaxis, angioedema, respiratory distress, or urticaria following administration of penicillin or cephalosporin 1

Treatment Algorithm for GBS Bacteriuria in Pregnancy with Amoxicillin Allergy

For patients NOT at high risk for anaphylaxis:

• Cefazolin: 2 g IV initial dose, then 1 g IV every 8 hours until delivery 1
  • Cefazolin is preferred because pharmacologic data suggest it achieves effective intraamniotic concentrations 1

For patients at high risk for anaphylaxis:

1. Obtain susceptibility testing for clindamycin and erythromycin on GBS isolates 1
2. Based on susceptibility results:
   • If isolate is susceptible to clindamycin: Clindamycin 900 mg IV every 8 hours until delivery 1
   • If isolate is resistant to clindamycin OR susceptibility testing is not available: Vancomycin 1 g IV every 12 hours until delivery 1
   • If isolate is susceptible to clindamycin but resistant to erythromycin: Test for inducible clindamycin resistance
     • If negative for inducible resistance: Use clindamycin
     • If positive for inducible resistance: Use vancomycin 1

Important Considerations

• Susceptibility testing is crucial: Resistance to clindamycin has been reported in 5-19% of GBS isolates 2, 3, and resistance to erythromycin can be as high as 31% 2
• Clearly label specimens: When collecting samples for culture, clearly identify the patient as penicillin allergic and specify that if GBS is isolated, it should be tested for susceptibility to clindamycin and erythromycin 1
• Avoid antepartum treatment: In the absence of GBS urinary tract infection, antimicrobial agents should not be used before the intrapartum period to treat GBS colonization as such treatment is not effective in eliminating carriage or preventing neonatal disease 1
• Duration of prophylaxis: For maximum effectiveness, antibiotics should be administered at least four hours before delivery 4
• Rising resistance concerns: Recent studies indicate increasing resistance to second-line antibiotics such as erythromycin and clindamycin, with several countries noting increased resistance rates in recent years 5

Pitfalls to Avoid

• Don't assume cross-reactivity: Not all patients allergic to amoxicillin will react to cephalosporins. Only those with history of severe reactions should avoid cephalosporins.
• Don't skip susceptibility testing: For patients at high risk for anaphylaxis, susceptibility testing is essential to guide appropriate antibiotic selection.
• Don't use erythromycin: The 2010 CDC guidelines no longer recommend erythromycin due to high rates of resistance and poor transplacental passage 1.
• Don't use oral antibiotics: Intravenous administration is required for adequate maternal and fetal levels.
• Don't assume all GBS isolates are susceptible to clindamycin: Always perform susceptibility testing when possible.

By following this evidence-based approach, the risk of early-onset GBS disease in neonates can be reduced by 80-95% 4.