Nitrofurantoin's Effectiveness Against Viridans Streptococcus
Nitrofurantoin is not specifically effective against viridans streptococcus, and alternative antibiotics should be used when treating infections caused by these organisms. While nitrofurantoin has demonstrated good in vitro activity against certain gram-positive organisms like enterococci, there is insufficient evidence supporting its efficacy against viridans streptococci specifically.
Antimicrobial Coverage of Nitrofurantoin
Nitrofurantoin is an antibiotic approved by the FDA in the 1950s for treatment of lower urinary tract infections 1. Its spectrum of activity includes:
- Good in vitro activity against vancomycin-resistant enterococci (VRE) 1, 2, 3
- Effective for uncomplicated urinary tract infections 4
- Recommended as first-line therapy for certain UTIs with a dosage of 100mg twice daily for 5 days 4
However, there is a notable absence of evidence regarding nitrofurantoin's effectiveness against viridans streptococci in the available literature.
Recommended Treatment for Viridans Streptococcal Infections
For viridans streptococcal infections, the following antibiotics have demonstrated efficacy:
- Penicillin-susceptible isolates: Penicillin/ampicillin or ceftriaxone 4
- Penicillin-resistant isolates: Vancomycin 4, 5
A study examining 129 blood culture isolates of viridans group streptococci found that all strains were susceptible to:
- Dalbavancin
- Daptomycin
- Linezolid
- Vancomycin 5
Clinical Implications
When treating infections caused by viridans streptococci:
- Obtain antimicrobial susceptibility testing to guide therapy
- For penicillin-susceptible isolates, use penicillin/ampicillin or ceftriaxone
- For penicillin-resistant isolates, vancomycin is the recommended treatment
- Newer antibiotics like daptomycin and linezolid have demonstrated high susceptibility rates
Important Considerations
- Viridans streptococci can cause serious infections including infective endocarditis, which requires targeted antimicrobial therapy 6
- Nitrofurantoin has potential serious adverse effects including immune-mediated liver injury 7
- Nitrofurantoin's utility is primarily limited to lower urinary tract infections due to its concentration in the urinary system rather than systemic distribution
Conclusion
Based on the available evidence, clinicians should not rely on nitrofurantoin for treating viridans streptococcal infections. Instead, they should use antibiotics with proven efficacy against these organisms, such as penicillin/ampicillin, ceftriaxone, or vancomycin, depending on susceptibility testing results.