What medication is recommended for a patient with a positive urine culture for group B strep (GBS) who is allergic to penicillin (PCN)?

Treatment for Group B Strep Urinary Tract Infection in Penicillin-Allergic Patients

For patients with a positive urine culture for Group B Streptococcus (GBS) who are allergic to penicillin, the recommended medication depends on the severity of the penicillin allergy, with cefazolin being the preferred agent for those without a history of severe allergic reactions, and vancomycin or clindamycin (if susceptible) for those with severe penicillin allergy.

Medication Selection Based on Allergy History

For Patients Without Severe Penicillin Allergy:

• Cefazolin is the preferred agent for penicillin-allergic patients who do not have a history of anaphylaxis, angioedema, respiratory distress, or urticaria following administration of penicillin or cephalosporin 1
• Dosing: 2g IV initial dose, then 1g IV every 8 hours until delivery (for pregnant patients) 1
• This recommendation is based on pharmacologic data suggesting cefazolin achieves effective concentrations 1

For Patients With Severe Penicillin Allergy:

Patients with a history of anaphylaxis, angioedema, respiratory distress, or urticaria following penicillin or cephalosporin administration are considered high risk for anaphylaxis and should receive:

• Vancomycin: 1g IV every 12 hours 1

  • Preferred when susceptibility testing is not available or when isolates are resistant to clindamycin 1
  • 100% of GBS isolates are susceptible to vancomycin 2

• Clindamycin: 900mg IV every 8 hours (only if isolate is confirmed susceptible) 1

  • Should only be used if susceptibility testing confirms the isolate is susceptible 1
  • Approximately 91% of GBS isolates are susceptible to clindamycin 2
  • Resistance to clindamycin has been increasing, with recent studies showing concerning resistance patterns 3

Susceptibility Testing Considerations

• Susceptibility testing should be performed on GBS isolates from penicillin-allergic patients at high risk for anaphylaxis 1
• Testing for inducible clindamycin resistance should be performed on isolates that are susceptible to clindamycin but resistant to erythromycin 1
• If an isolate is resistant to erythromycin, it might have inducible resistance to clindamycin, even if it appears susceptible 1
• Erythromycin is not recommended as first-line therapy due to increasing resistance rates (approximately 21% of isolates are resistant) 2, 4

Important Clinical Considerations

• GBS in urine at concentrations of ≥10⁴ colony-forming units/ml should be reported and treated 1
• Antimicrobial agents should not be used before the intrapartum period to treat GBS colonization in pregnant women (except for UTI), as such treatment is not effective in eliminating carriage or preventing neonatal disease 1
• For non-pregnant adults with GBS UTI, the same antibiotic selection principles apply based on allergy history 4
• All GBS isolates remain 100% susceptible to penicillin, ampicillin, cefazolin, and vancomycin, making these reliable options when not contraindicated by allergies 2, 3

Pitfalls and Caveats

• Do not use erythromycin empirically for treatment of GBS in penicillin-allergic patients due to increasing resistance rates 2, 4
• Always verify susceptibility results before using clindamycin, particularly in areas with high resistance rates 1, 3
• The positive predictive value of antenatal GBS cultures is lower than previously reported, which may affect treatment decisions in pregnant women 2
• Resistance to clindamycin and erythromycin among GBS isolates has been increasing, necessitating careful antibiotic selection 1, 3