What is the best medication to treat a urinary tract infection (UTI) caused by Streptococcus agalactiae (Group B streptococcus)?

Treatment of Urinary Tract Infection Caused by Streptococcus agalactiae (Group B Streptococcus)

Ampicillin is the first-line treatment for urinary tract infections caused by Streptococcus agalactiae (Group B Streptococcus), with a dosage of 500 mg orally every 6 hours for 5-7 days for uncomplicated infections. 1, 2, 3

First-Line Treatment Options

Penicillins

• Ampicillin: 500 mg orally every 6 hours for 5-7 days (uncomplicated UTI) 1, 2
  • Multiple studies demonstrate >95% sensitivity of Group B Streptococcus to ampicillin 2, 3, 4
  • For complicated UTIs, treatment should be extended to 10-14 days 5
• Amoxicillin-clavulanic acid: Alternative first-line option recommended by WHO for GBS UTIs 5

Alternative Treatment Options (for Penicillin-Allergic Patients)

Non-Anaphylactic Penicillin Allergy

• Cefazolin: 2 g IV initial dose, then 1 g IV every 8 hours until resolution (for hospitalized patients) 6
• Nitrofurantoin: 100 mg orally every 6 hours for 5-7 days 5, 7
  • 95.5% sensitivity reported in clinical studies 7

Anaphylactic Penicillin Allergy

• Vancomycin: 1 g IV every 12 hours (for severe infections requiring hospitalization) 6, 8
  • 95-100% sensitivity reported in multiple studies 3, 7
• Clindamycin: Only if susceptibility testing confirms sensitivity, as resistance rates up to 77.3% have been reported 3, 4

Important Considerations

Susceptibility Testing

• Susceptibility testing is essential for penicillin-allergic patients due to increasing resistance to alternative antibiotics 5
• Resistance patterns to consider:
  • High resistance to tetracycline (81.6%) and co-trimoxazole (68.9%) 7
  • Variable resistance to clindamycin (17.2-77.3%) and erythromycin (21.1%) 3, 4

Special Populations

• Pregnant women: Penicillin G remains the drug of choice for GBS infections during pregnancy 6
  • 5 million units IV initial dose, then 2.5-3.0 million units IV every 4 hours until delivery
• Complicated UTIs: Extended treatment duration (10-14 days) is recommended 5

Identifying and Treating Reservoirs

• Check for potential GBS reservoirs that may cause recurrent infection:
  • Vaginal colonization in women
  • Urethral colonization in men
  • Gastrointestinal tract 2, 9
• For women with concurrent vaginal colonization, consider topical treatment with chlorhexidine 2% solution 9

Treatment Algorithm

1. Confirm diagnosis: Positive urine culture with ≥10^5 CFU/ml of Streptococcus agalactiae
2. Assess patient for penicillin allergy:
   • No allergy → Ampicillin 500 mg orally every 6 hours
   • Non-anaphylactic allergy → Nitrofurantoin 100 mg orally every 6 hours
   • Anaphylactic allergy → Obtain susceptibility testing and use vancomycin if hospitalization required
3. Determine treatment duration:
   • Uncomplicated UTI: 5-7 days
   • Complicated UTI: 10-14 days
4. Screen for and treat potential reservoirs to prevent recurrence

The high sensitivity of Group B Streptococcus to penicillins makes ampicillin the optimal choice for treatment, with multiple studies consistently showing >95% susceptibility rates 2, 3, 4.