Group B Streptococcus Sensitivity to Nitrofurantoin
Group B Streptococcus (GBS) demonstrates high susceptibility to nitrofurantoin, with 95-100% of clinical isolates showing sensitivity in multiple studies, making it an appropriate treatment option for GBS urinary tract infections in non-pregnant patients. 1, 2
Antimicrobial Susceptibility Evidence
High Sensitivity Rates
- A 2012 Iranian study of GBS urine isolates found 95.5% sensitivity to nitrofurantoin 1
- A 2004 study of 52 clinical GBS isolates demonstrated 100% sensitivity to nitrofurantoin, with only one isolate (2%) showing intermediate sensitivity 2
- A 2018 Chinese study reported 18.5% of isolates were nonsusceptible to nitrofurantoin, though no known nitrofurantoin resistance genes were identified in these strains 3
Comparative Activity
- Historical data from 1982 showed MIC values for nitrofurantoin against GBS ranging from 8 to >64 mg/L, with similar susceptibility patterns between urinary and non-urinary isolates 4
- GBS maintains significantly better sensitivity to nitrofurantoin compared to tetracyclines (74-81% resistance), erythromycin (63% resistance), and clindamycin (44% resistance) 3, 1
Clinical Context and Limitations
Appropriate Use in Urinary Tract Infections
- Nitrofurantoin is recommended as a first-line agent for uncomplicated UTIs in non-pregnant women 5
- The 2004 study specifically recommended nitrofurantoin for patients with GBS bacteriuria 2
- Nitrofurantoin achieves high urinary concentrations, making it effective for lower urinary tract infections despite variable serum levels 5
Critical Pregnancy Considerations
- For pregnant women with GBS bacteriuria, nitrofurantoin may be used to treat the acute UTI, but does NOT replace the mandatory requirement for intravenous intrapartum antibiotic prophylaxis during labor 6, 7
- Penicillin G or ampicillin remain the preferred agents for intrapartum prophylaxis, not nitrofurantoin 6, 7
- Treatment of GBS UTI during pregnancy does not eliminate genital tract colonization, necessitating IV prophylaxis regardless of prior treatment 6
Common Pitfalls to Avoid
- Do not use nitrofurantoin for systemic GBS infections or bacteremia, as it achieves inadequate serum levels due to large volume of distribution 5
- Do not assume nitrofurantoin treatment eliminates GBS colonization in pregnant women—intrapartum IV prophylaxis remains mandatory 6
- The 18.5% nonsusceptibility rate in the Chinese study suggests emerging resistance patterns may vary geographically, warranting susceptibility testing when available 3
- Nitrofurantoin should be reserved for lower urinary tract infections only, not for pyelonephritis or complicated UTIs 5