What are the recommended antibiotics for streptococcus (strep) viridans urinary tract infection (UTI)?

Antibiotic Treatment for Streptococcus Viridans UTI

For urinary tract infections caused by Streptococcus viridans (viridans group streptococci), amoxicillin 500 mg orally every 8 hours is the recommended first-line treatment, as penicillins remain the drugs of choice for streptococcal infections with high susceptibility rates.

Primary Treatment Recommendations

First-Line Therapy

• Amoxicillin 500 mg orally every 8 hours for 7 days is the preferred oral agent, as it achieves high urinary concentrations effective against viridans streptococci 1
• Ampicillin 500 mg orally every 8 hours is an equivalent alternative to amoxicillin for streptococcal UTIs 1
• Viridans streptococci show 100% susceptibility to amoxicillin in the S. milleri group and 67-84% susceptibility in other viridans species 2

Alternative Oral Options

• Nitrofurantoin 100 mg orally every 6 hours for 7 days is an effective alternative with good in vitro activity against streptococci and FDA approval for lower urinary tract infections 3, 1
• Ceftriaxone demonstrates 94-100% susceptibility against most viridans streptococci species, making third-generation cephalosporins a reasonable alternative 2

Susceptibility Considerations

Penicillin Resistance Patterns

• S. milleri shows 100% penicillin susceptibility, making it highly predictable to treat 2
• S. sanguis demonstrates 74% penicillin susceptibility, requiring consideration of local resistance patterns 2
• S. mitis has lower susceptibility at 42% to penicillin, potentially necessitating alternative agents 2

When to Consider Vancomycin

• Vancomycin should be reserved for documented penicillin-resistant isolates, as all viridans streptococci maintain 100% vancomycin susceptibility 2
• Local susceptibility patterns must guide initial therapy, particularly in institutions with known penicillin resistance 4

Important Clinical Caveats

Avoid These Pitfalls

• Do not use trimethoprim-sulfamethoxazole for prolonged treatment (>2 weeks), as resistance develops rapidly in streptococcal UTIs, even when initially susceptible 5
• Fluoroquinolones (levofloxacin, ofloxacin) show high in vitro activity but should be reserved for resistant cases given FDA warnings about unfavorable risk-benefit ratios for uncomplicated UTIs 1, 2
• Fosfomycin is FDA-approved specifically for E. faecalis UTIs but lacks specific data for viridans streptococci 1

Monitoring Requirements

• Confirm susceptibility testing to guide definitive therapy, as resistance patterns vary significantly between viridans species 2
• For patients on nitrofurantoin, monitor for pulmonary reactions, hepatic toxicity, and gastrointestinal disturbances 6
• Complete the full 7-day course to ensure eradication and prevent relapse 6

Treatment Algorithm

1. Start empiric amoxicillin 500 mg every 8 hours while awaiting culture results 1
2. Adjust based on susceptibility testing if penicillin resistance is documented 2
3. Switch to vancomycin only for confirmed penicillin-resistant isolates 4, 2
4. Consider nitrofurantoin as first alternative if penicillin allergy or intolerance exists 3, 1