What is the recommended treatment for a patient with a Group B strep (Streptococcus agalactiae) urinary tract infection (UTI) and a penicillin allergy?

Treatment of Group B Streptococcal UTI in Patients with Penicillin Allergy

For patients with Group B streptococcal (GBS) urinary tract infection and penicillin allergy, the recommended treatment depends on the severity of the penicillin allergy, with vancomycin being the preferred agent for those with severe penicillin allergy when susceptibility testing is unavailable or shows resistance to clindamycin.

Assessment of Penicillin Allergy Severity

The first step in management is determining the severity of the penicillin allergy:

• Low-risk for anaphylaxis: No history of immediate hypersensitivity reactions (anaphylaxis, angioedema, respiratory distress, or urticaria)
• High-risk for anaphylaxis: History of immediate hypersensitivity reactions to penicillin or cephalosporins

Treatment Algorithm

For patients with low-risk penicillin allergy:

• First-line: Cefazolin 1-2g IV every 8 hours or appropriate oral cephalosporin 1
  • Cross-reactivity between penicillins and cephalosporins occurs in only about 10% of patients 2
  • First-generation cephalosporins are acceptable for penicillin-allergic patients without immediate hypersensitivity 1

For patients with high-risk penicillin allergy:

1. Obtain susceptibility testing for clindamycin and erythromycin if possible 1
2. If isolate is susceptible to clindamycin:
   • Clindamycin 900mg IV every 8 hours or 300-450mg orally 3-4 times daily 1
   • Important: Test for inducible clindamycin resistance using D-zone test if isolate is erythromycin-resistant but clindamycin-susceptible 1
3. If susceptibility testing unavailable OR isolate resistant to clindamycin OR shows inducible resistance:
   • Vancomycin 1g IV every 12 hours 1

Important Considerations

• Rising resistance rates: Recent studies show increasing resistance to macrolides and clindamycin among GBS isolates:

  • Erythromycin resistance has increased from 15.8% to 32.8% 3
  • Clindamycin resistance has increased from 10.5% to 15.0% 3
  • In some studies, erythromycin resistance was found in 21% of isolates 4

• Susceptibility testing is crucial: Only 11% of penicillin-allergic patients with GBS had appropriate antimicrobial sensitivity testing in one study 5, highlighting the importance of obtaining susceptibility results

• Avoid erythromycin: Despite being mentioned in older guidelines, erythromycin should not be used empirically due to high resistance rates 2, 3

• All GBS isolates remain susceptible to penicillin: No resistance to penicillin, ampicillin, cefazolin, cefotaxime, or vancomycin has been documented in GBS 6, 3, 4

Monitoring and Follow-up

• Obtain urine culture after treatment completion to confirm eradication
• For pregnant women with GBS bacteriuria, follow CDC guidelines for intrapartum prophylaxis regardless of whether they received treatment earlier in pregnancy 1
• Monitor for clinical response within 48-72 hours of initiating therapy

Pitfalls to Avoid

• Don't use erythromycin empirically due to high resistance rates
• Don't use clindamycin without susceptibility testing as approximately 20% of GBS isolates are resistant 2
• Don't forget to test for inducible clindamycin resistance when considering clindamycin for treatment 1, 2
• Don't assume all cephalosporins are safe in patients with severe penicillin allergy; avoid them in patients with history of anaphylaxis to penicillin 2

By following this evidence-based approach, clinicians can effectively treat GBS UTI in penicillin-allergic patients while minimizing the risk of treatment failure due to antimicrobial resistance.