What is the appropriate treatment for a urinary tract infection caused by Viridans streptococcus group?

Treatment of Urinary Tract Infection Caused by Viridans Streptococcus Group

Amoxicillin or ampicillin is the first-line treatment for urinary tract infections caused by viridans streptococcus group, with penicillin G as an alternative for more severe infections requiring intravenous therapy. 1

Antibiotic Selection Algorithm

First-line Options:

• Oral therapy:
  • Amoxicillin 500 mg three times daily for 7 days
  • Amoxicillin-clavulanate 500/125 mg three times daily for 7 days (if beta-lactamase production is suspected)

Alternative Options (for penicillin-allergic patients):

• Oral therapy:
  • Trimethoprim-sulfamethoxazole 160/800 mg twice daily for 7 days
  • Nitrofurantoin 100 mg twice daily for 5-7 days (for uncomplicated lower UTI only)
  • Levofloxacin 500 mg daily for 7 days

For Severe Infections or Inpatient Treatment:

• Intravenous therapy:
  • Ampicillin 2 g every 4-6 hours
  • Penicillin G 12-18 million units/24 hours (divided in 4-6 doses)
  • Vancomycin 15-20 mg/kg every 12 hours (for penicillin-allergic patients)

Treatment Duration

• Uncomplicated lower UTI: 5-7 days
• Complicated UTI or pyelonephritis: 10-14 days

Special Considerations

Penicillin Resistance

For viridans streptococcus with penicillin MIC ≥0.5 μg/mL, treatment should follow recommendations similar to those for enterococcal infections 2:

• Aqueous crystalline penicillin G sodium 24 million U/24 h IV (continuously or in 4-6 divided doses) for 4 weeks
• Plus gentamicin 3 mg/kg per 24 h IV/IM for 2 weeks

Penicillin Allergy

For patients with true penicillin allergy:

• Vancomycin 30 mg/kg per 24 h IV in 2 equally divided doses 2
• Vancomycin should be infused over at least 1 hour to reduce the risk of "red man syndrome" 2

Clinical Pearls and Pitfalls

Important Considerations:

1. Susceptibility testing: Viridans streptococci can have variable susceptibility patterns, so treatment should be guided by susceptibility results when available.

2. Misidentification risk: Viridans streptococci are sometimes misidentified in the laboratory or confused with other streptococci 3, 4. Ensure proper identification through appropriate laboratory techniques.

3. Biofilm formation: Viridans streptococci can form biofilms on urinary catheters, which may require catheter removal for successful treatment.

4. Endocarditis risk: Although rare, viridans streptococci from UTIs can cause endocarditis in high-risk patients. Consider echocardiography in patients with persistent bacteremia or risk factors for endocarditis.

Pitfalls to Avoid:

1. Don't use cephalosporins as monotherapy: Some viridans streptococci have reduced susceptibility to cephalosporins 2, 1.

2. Avoid fluoroquinolones for empiric therapy: High rates of resistance have been reported in some viridans streptococcal strains 1.

3. Don't dismiss as contamination: Viridans streptococci in urine are sometimes incorrectly dismissed as contaminants, leading to delayed treatment 4, 5.

4. Avoid nitrofurantoin in renal impairment: Should not be used in patients with creatinine clearance <30 mL/min 1.

Follow-up Recommendations

• Repeat urine culture 1-2 weeks after completing treatment to confirm eradication
• For recurrent infections, consider urologic evaluation to identify anatomical abnormalities or foreign bodies

Viridans streptococcal UTIs are uncommon but require appropriate antibiotic therapy based on susceptibility patterns. While they are typically less virulent than other uropathogens, proper identification and treatment are essential to prevent complications and recurrence.