What is the recommended dose of amoxicillin (amoxicillin) for a Group B strep (Streptococcus agalactiae) urinary tract infection (UTI)?

Amoxicillin Dosing for Group B Streptococcus Urinary Tract Infection

For uncomplicated Group B Streptococcus (GBS) urinary tract infections, amoxicillin 500 mg orally every 8 hours for 7-10 days is the recommended treatment regimen. 1

First-Line Treatment Options for GBS UTI

GBS (Streptococcus agalactiae) remains highly susceptible to beta-lactam antibiotics, making amoxicillin an excellent first-line choice:

• Amoxicillin: 500 mg PO every 8 hours for 7-10 days 1
• Ampicillin: 2 g IV initial dose, then 1 g IV every 4-6 hours (for severe infections requiring hospitalization) 2

Special Considerations

Severity-Based Approach

1. Uncomplicated cystitis:

   • Amoxicillin 500 mg PO every 8 hours for 7-10 days 1
   • Alternative: Nitrofurantoin 100 mg PO every 6 hours 1

2. Complicated UTI/Pyelonephritis:

   • Consider initial IV therapy with ampicillin 2 g IV, followed by oral amoxicillin 2
   • Duration: 10-14 days total therapy

Penicillin Allergy

For patients with penicillin allergy:

• Non-severe allergy: Cefazolin 1-2 g IV every 8 hours or oral cephalexin 500 mg every 6 hours 1
• Severe allergy: Clindamycin 600 mg IV/PO every 8 hours (if susceptible) or vancomycin 15-20 mg/kg IV every 12 hours 2

Pregnancy Considerations

GBS bacteriuria during pregnancy requires special attention:

• Treat symptomatic or asymptomatic bacteriuria with colony counts ≥100,000 CFU/mL 3
• Women with documented GBS bacteriuria during pregnancy (regardless of colony count) should receive intrapartum antibiotic prophylaxis during labor 2, 3
• No re-screening is needed for women with documented GBS bacteriuria as they are presumed to remain colonized 3

Antibiotic Susceptibility

GBS remains highly susceptible to beta-lactam antibiotics. A comprehensive study of clinical GBS isolates showed:

• Nearly universal susceptibility to penicillins and amoxicillin 4
• Rare resistance to macrolides (1.4-3.5%) 4
• High resistance to tetracyclines (>70%) 4

Treatment Failure Considerations

If treatment fails:

1. Obtain urine culture with susceptibility testing
2. Consider structural abnormalities or complicated infection
3. Consider alternative regimens based on susceptibility:
   • Fosfomycin 3 g PO single dose (for uncomplicated cases) 1
   • Fluoroquinolones (if susceptible) 1

Common Pitfalls to Avoid

1. Undertreating: Short courses (<7 days) may lead to treatment failure with GBS UTI
2. Ignoring pregnancy status: GBS bacteriuria in pregnancy requires specific management and follow-up
3. Missing susceptibility testing: While resistance to beta-lactams is rare in GBS, always confirm susceptibility in treatment failures
4. Overlooking asymptomatic bacteriuria in pregnancy: This requires treatment when GBS is identified, regardless of colony count

Amoxicillin remains highly effective against GBS, with minimal resistance reported in clinical studies, making it an excellent first-line choice for uncomplicated GBS UTIs when used at appropriate dosing.