Treatment of Group B Streptococcal Urinary Tract Infection
Penicillin G or ampicillin is the first-line treatment for GBS UTI in non-pregnant adults, with a typical regimen of ampicillin 500 mg orally every 6 hours for 7-10 days, or penicillin V 500 mg orally every 6-8 hours for 7-10 days. 1, 2, 3
First-Line Antibiotic Selection
Penicillin G remains the preferred agent due to its narrow spectrum of activity and high efficacy against GBS, which continues to show universal susceptibility to penicillin. 1, 2
Ampicillin is an acceptable alternative to penicillin G, with FDA-approved dosing for genitourinary infections of 500 mg orally four times daily in equally spaced doses. 3
Complete the full prescribed course (typically 7-10 days) to ensure complete eradication and prevent recurrence—premature discontinuation is a common pitfall leading to treatment failure. 1, 2
Management in Pregnant Women: Critical Distinction
Any concentration of GBS bacteriuria during pregnancy—regardless of colony count—mandates intrapartum antibiotic prophylaxis during labor, not immediate treatment of the UTI itself. 2
GBS bacteriuria at any point in pregnancy serves as a marker for heavy genital tract colonization and significantly increases risk for early-onset neonatal disease. 2
Intrapartum prophylaxis should be administered for ≥4 hours before delivery, which is 78% effective in preventing early-onset GBS disease. 2
Do not treat asymptomatic GBS bacteriuria before the intrapartum period—antimicrobial agents should not be used to treat asymptomatic colonization outside of labor. 1
The recommended intrapartum regimen is penicillin G 5 million units IV initially, then 2.5-3.0 million units IV every 4 hours until delivery, or ampicillin 2 g IV initially, then 1 g IV every 4 hours until delivery. 4
Penicillin-Allergic Patients: Risk-Stratified Approach
Low Risk for Anaphylaxis
Cefazolin or cephalexin is the preferred alternative for patients with penicillin allergy who do not have a history of anaphylaxis, angioedema, respiratory distress, or urticaria. 1, 2
Cefazolin dosing: 2 g IV initial dose, then 1 g IV every 8 hours (for intrapartum prophylaxis). 4
High Risk for Anaphylaxis
Clindamycin is preferred if the GBS isolate is confirmed susceptible (900 mg IV every 8 hours for intrapartum prophylaxis, or 300-450 mg orally every 6 hours for UTI treatment). 4, 1, 5
Vancomycin should be used for severe infections or when susceptibility results are unavailable (1 g IV every 12 hours). 4, 1
Critical pitfall: Approximately 20% of GBS isolates are resistant to clindamycin—susceptibility testing is mandatory before using this antibiotic. 1, 6, 2
Essential Susceptibility Testing
Always perform susceptibility testing on GBS isolates from penicillin-allergic patients at high risk for anaphylaxis before selecting alternative therapy. 1
Test for inducible clindamycin resistance for isolates that are susceptible to clindamycin but resistant to erythromycin—resistance to erythromycin is often but not always associated with clindamycin resistance. 4, 1
Erythromycin is not recommended due to increasing GBS resistance to macrolide antibiotics. 4
Common Clinical Pitfalls
Underdosing or premature discontinuation leads to treatment failure and recurrence—ensure full course completion. 1, 2
Using clindamycin without susceptibility testing risks treatment failure due to the 20% resistance rate. 1, 2
Treating asymptomatic GBS bacteriuria in non-pregnant patients is unnecessary and promotes antibiotic resistance—only treat symptomatic UTI. 2
Failing to provide intrapartum prophylaxis to pregnant women with any GBS bacteriuria increases neonatal mortality risk—this is the single most important intervention in pregnancy. 2
Failure to consider local resistance patterns when selecting empiric therapy could lead to treatment failure, though GBS resistance to penicillin remains virtually nonexistent. 1