What antibiotic is used to treat group B strep (Streptococcus agalactiae) urinary tract infection (UTI)?

Treatment of Group B Streptococcus Urinary Tract Infection

For Group B Streptococcus (GBS) urinary tract infections, penicillin G or ampicillin should be used as first-line therapy, with penicillin G being preferred due to its narrower spectrum of activity and lower likelihood of selecting for resistant organisms. 1

First-Line Treatment Options

Preferred Agents:

• Penicillin G: 5 million units IV initially, then 2.5-3.0 million units IV every 4 hours 1, 2
• Ampicillin: 2 g IV initially, then 1 g IV every 4 hours 1

Treatment Duration:

• Uncomplicated UTI: 7-10 days
• Complicated UTI or pyelonephritis: 10-14 days
• Continue treatment for at least 48-72 hours after symptom resolution 1

Alternative Options for Penicillin-Allergic Patients

For patients with non-severe penicillin allergy:

• Cefazolin: 2 g IV initial dose, then 1 g IV every 8 hours 1

For patients with high risk of anaphylaxis:

• Clindamycin: 900 mg IV every 8 hours (only if susceptibility testing confirms sensitivity) 1, 2
• Vancomycin: 1 g IV every 12 hours (for clindamycin-resistant strains) 1, 3

For uncomplicated lower UTIs:

• Nitrofurantoin: Can be effective for uncomplicated lower UTIs 1, 4

Antibiotic Resistance Considerations

All GBS isolates remain susceptible to penicillin, ampicillin, cefazolin, and vancomycin 5. However, resistance to alternative agents is increasing:

• Clindamycin resistance: Increased from 10.5% to 15.0% 5
• Erythromycin resistance: Increased from 15.8% to 32.8% 5

Therefore, susceptibility testing is essential when using non-beta-lactam antibiotics, particularly for penicillin-allergic patients 1.

Special Considerations

Pregnant Patients

• Any amount of GBS in urine during pregnancy indicates heavy colonization
• Requires both immediate treatment of the current infection and intrapartum prophylaxis during labor 1
• Obtain urine culture after completion of treatment to confirm eradication 1
• Intrapartum prophylaxis is required regardless of whether the patient received treatment earlier in pregnancy 1

Antibiotic Selection Rationale

Penicillin G is preferred over ampicillin because:

• It has a narrower spectrum of antimicrobial activity
• Less likely to select for resistant organisms 6
• Both achieve adequate levels in the fetal circulation and amniotic fluid 2

Follow-up

• Obtain a urine culture after completion of treatment to confirm eradication of the infection 1
• For pregnant women, intrapartum prophylaxis is still required even if the UTI was successfully treated earlier in pregnancy 1

Common Pitfalls to Avoid

1. Failing to perform susceptibility testing for penicillin-allergic patients
2. Using erythromycin without susceptibility testing due to high resistance rates
3. Not obtaining follow-up cultures to confirm eradication
4. Forgetting intrapartum prophylaxis for pregnant women with history of GBS bacteriuria
5. Using fluoroquinolones as first-line therapy when better alternatives exist 1

By following these evidence-based recommendations, clinicians can effectively treat GBS UTIs while minimizing the risk of treatment failure and antibiotic resistance.