How should I treat a urinary tract infection caused by Group B Streptococcus in a patient with a true allergy to penicillins and cephalosporins?

Treatment of Group B Streptococcus UTI in Penicillin and Cephalosporin-Allergic Patients

For patients with true allergy to both penicillins and cephalosporins, vancomycin 1g IV every 12 hours is the recommended treatment for Group B Streptococcus urinary tract infection, with clindamycin 900mg IV every 8 hours as an alternative only if susceptibility testing confirms the isolate is susceptible to both clindamycin and erythromycin. 1, 2

Immediate Action Required

Order susceptibility testing for clindamycin and erythromycin immediately upon isolating GBS from a penicillin-allergic patient. 3, 1 This is critical because clindamycin resistance ranges from 3-15% among GBS isolates, and you cannot safely use clindamycin without confirmed susceptibility. 1, 4

D-Zone Testing Is Mandatory

If the isolate is erythromycin-resistant but appears clindamycin-susceptible, demand D-zone testing to detect inducible clindamycin resistance. 3, 1, 2 Isolates with inducible resistance will fail clindamycin therapy despite appearing susceptible on standard testing. 1

Treatment Algorithm Based on Susceptibility Results

If Susceptibility Results Are Available:

• Use clindamycin 900mg IV every 8 hours if the isolate is susceptible to both clindamycin AND erythromycin, with no inducible resistance detected. 1, 2
• Use vancomycin 1g IV every 12 hours if the isolate shows any resistance to clindamycin or erythromycin, demonstrates inducible clindamycin resistance, or if susceptibility is unknown. 1, 2

If Susceptibility Results Are Not Yet Available:

Start vancomycin 1g IV every 12 hours empirically while awaiting susceptibility results. 1 This is the safest approach given the 3-15% clindamycin resistance rate and the potential for inducible resistance. 1, 4

Critical Allergy Clarification

Before accepting the allergy label at face value, verify the patient truly has a high-risk allergy. High-risk penicillin allergy is defined as a history of anaphylaxis, angioedema, respiratory distress, or urticaria following penicillin or cephalosporin administration. 3, 1

If the Patient Does NOT Have High-Risk Allergy Features:

Consider cefazolin 2g IV initially, then 1g IV every 8 hours, as cross-reactivity between penicillins and cephalosporins is only approximately 10%. 1, 5 However, since your question specifies allergy to both classes, this option is not applicable in your case.

Alternative Beta-Lactam Considerations:

Aztreonam can be used in patients with penicillin and cephalosporin allergy, as there is little to no immunologic cross-reactivity between penicillins and monobactams. 3, 5 However, aztreonam is not typically first-line for GBS UTI and should be reserved for situations where vancomycin and clindamycin are not options.

Carbapenems can also be safely used in patients with confirmed penicillin allergy, as cross-reactivity is minimal. 3, 5 Ertapenem 1g IV daily would provide adequate GBS coverage, though this is not standard first-line therapy.

Special Considerations for Pregnancy

If the patient is pregnant, any GBS detected in urine at ≥10⁴ CFU/mL mandates immediate treatment AND requires intrapartum IV antibiotic prophylaxis during labor, regardless of whether the UTI was treated. 1, 2 The prenatal treatment does not eliminate the need for intrapartum prophylaxis. 2

Do not use oral antibiotics before labor to eradicate GBS colonization—this approach is ineffective and should never be employed. 1, 2

Resistance Patterns and Reassurance

All GBS isolates worldwide remain 100% susceptible to penicillin—no confirmed penicillin resistance has ever been documented. 1, 4, 6 This makes the allergy particularly unfortunate, as penicillin G or ampicillin would otherwise be ideal therapy.

Fluoroquinolone resistance is increasing (12.8% in some studies), particularly in men and non-pregnant women, making fluoroquinolones unreliable for empiric GBS UTI treatment. 6 Do not use ciprofloxacin or levofloxacin for GBS UTI.

Nitrofurantoin shows excellent activity against GBS (98% susceptibility) and can be considered for uncomplicated lower UTI in non-pregnant patients, though it is not appropriate for pyelonephritis or bacteremia. 7 However, given your patient's dual allergy requiring IV therapy, nitrofurantoin is likely not the optimal choice unless this is a simple cystitis in a non-pregnant patient.

Common Pitfalls to Avoid

• Never assume clindamycin will work without susceptibility testing—resistance is too common. 1, 4
• Never skip D-zone testing on erythromycin-resistant, clindamycin-susceptible isolates—inducible resistance will cause treatment failure. 3, 1
• Never use oral antibiotics for GBS eradication in pregnancy—only intrapartum IV prophylaxis is effective. 1, 2
• Never use fluoroquinolones empirically for GBS—resistance rates are too high. 6