What is the appropriate treatment for a Group B Streptococcus (GBS) urinary tract infection (UTI) in a patient with an anaphylactic reaction to penicillin?

Treatment of GBS UTI in Patients with Anaphylaxis to Penicillin

For patients with anaphylactic penicillin allergy and GBS UTI, vancomycin 1g IV every 12 hours is the recommended treatment when susceptibility testing is unavailable or pending, while clindamycin 900 mg IV every 8 hours should be used if the isolate is confirmed susceptible to both clindamycin and erythromycin. 1

Defining Anaphylactic Penicillin Allergy

Before selecting alternative antibiotics, confirm the patient has true anaphylaxis, characterized by: 2, 1

• History of anaphylaxis following penicillin or cephalosporin administration
• Angioedema after penicillin or cephalosporin exposure
• Respiratory distress following penicillin or cephalosporin administration
• Urticaria after penicillin or cephalosporin exposure

Critical caveat: Cefazolin should NOT be used in patients with anaphylactic penicillin allergy due to cross-reactivity risk, despite its excellent activity against GBS. 1 Approximately 10% of patients with penicillin allergy have immediate hypersensitivity reactions to cephalosporins. 2

Treatment Algorithm for GBS UTI with Anaphylactic Penicillin Allergy

Step 1: Obtain Susceptibility Testing

Always obtain antimicrobial susceptibility testing for clindamycin and erythromycin on the GBS isolate. 2, 1 This is mandatory according to CDC guidelines for penicillin-allergic patients at high risk for anaphylaxis. 2

Step 2: Select Antibiotic Based on Susceptibility Results

If susceptibility testing shows the isolate is susceptible to both clindamycin AND erythromycin:

• Use clindamycin 900 mg IV every 8 hours 2, 1
• Continue treatment for at least 10 days for beta-hemolytic streptococcal infections 3

If susceptibility testing is unavailable, pending, or shows resistance to clindamycin or erythromycin:

• Use vancomycin 1g IV every 12 hours 2, 1
• Vancomycin should be reserved for cases where no other options exist due to antimicrobial resistance concerns 2

Step 3: Special Considerations for Resistance Detection

Perform D-zone testing on isolates that are erythromycin-resistant but clindamycin-susceptible to detect inducible clindamycin resistance. 2 This is critical because resistance to erythromycin is frequently but not always associated with clindamycin resistance. 4

Understanding GBS Resistance Patterns

The resistance landscape for GBS has evolved significantly:

Clindamycin and erythromycin resistance is increasingly common: 4

• Resistance to erythromycin ranges from 7-25% among invasive GBS isolates
• Resistance to clindamycin ranges from 3-15% among invasive GBS isolates
• Recent data from Polish adults with GBS UTI showed 22% erythromycin resistance and 18% clindamycin resistance 5
• The cMLSB phenotype (constitutive macrolide-lincosamide-streptogramin B resistance) was present in 76% of resistant strains 5

Penicillin resistance remains absent: All GBS isolates worldwide remain susceptible to penicillin, with no confirmed resistance to penicillin or ampicillin observed to date. 4

Clinical Pitfalls and Monitoring

Monitor for Clostridioides difficile-associated diarrhea (CDAD) when using clindamycin, as it has been reported with nearly all antibacterial agents and may range from mild diarrhea to fatal colitis. 3 If significant diarrhea occurs during therapy, discontinue the antibiotic. 3

Consider monitoring renal function when using vancomycin, particularly in patients with pre-existing renal dysfunction or those taking concomitant nephrotoxic drugs, as clindamycin is potentially nephrotoxic. 3

Consider infectious disease consultation for complicated cases or when limited treatment options are available. 1 This is particularly important given the high rates of multidrug resistance (33.6%) observed in GBS UTI isolates, with particularly high resistance to tetracycline (81.5%), azithromycin (44.5%), erythromycin (36.3%), and clindamycin (26%). 6