Nitrofurantoin (Macrobid) for Group B Streptococcus UTI
Nitrofurantoin has good in vitro activity against Group B Streptococcus (GBS) and is an appropriate treatment option for uncomplicated lower urinary tract infections caused by GBS, though clinical data specifically for GBS UTI is limited. 1
Antimicrobial Activity and Clinical Evidence
Nitrofurantoin demonstrates activity against Enterococcus species and maintains good susceptibility profiles against common uropathogens, including streptococcal species. 2, 3
- The drug has retained excellent activity for over 60 years against various UTI pathogens including Enterococcus species, which are closely related to GBS 2
- Clinical studies have documented successful treatment of urinary infections caused by Streptococcus faecalis (an enterococcal species) with nitrofurantoin, achieving cure rates of 85-94% 4
- Nitrofurantoin achieves high urinary concentrations that exceed therapeutic levels by 25- to 100-fold, making it particularly effective for lower urinary tract infections 1
Treatment Recommendations
For uncomplicated lower UTI caused by GBS, nitrofurantoin 100 mg orally twice daily for 5-7 days is the recommended regimen. 5, 2
- Nitrofurantoin is recommended as first-line therapy for uncomplicated cystitis in current treatment guidelines 5, 2, 6
- The standard dosing is 100 mg three to four times daily for 7 days, with cure rates exceeding 85% 4
- Shorter courses of 5 days may be adequate for uncomplicated cystitis 5
Critical Limitations and Contraindications
Nitrofurantoin should ONLY be used for lower urinary tract infections (cystitis) and is contraindicated for pyelonephritis, complicated UTIs, and in patients with any degree of renal impairment. 2, 6
- The drug does not achieve adequate tissue concentrations outside the urinary tract and should never be used for systemic GBS infections or pyelonephritis 2
- Absolute contraindications include renal impairment of any degree and the last trimester of pregnancy (after 36 weeks gestation) 2
- Nitrofurantoin is contraindicated in the last three months of pregnancy, which is particularly relevant since GBS screening occurs at 35-37 weeks 1, 2
Special Considerations for GBS
If GBS bacteriuria is detected during pregnancy at any concentration, this indicates a need for intrapartum antibiotic prophylaxis with penicillin or ampicillin, not treatment with nitrofurantoin during pregnancy. 1
- Pregnant women with GBS bacteriuria should receive intrapartum penicillin G (5 million units IV initial dose, then 2.5 million units IV every 4 hours) or ampicillin (2 g IV initial dose, then 1 g IV every 4 hours) during labor 1
- Antimicrobial agents should not be used before the intrapartum period to treat asymptomatic GBS colonization, as this is ineffective in preventing neonatal disease 1
- For penicillin-allergic women at low risk of anaphylaxis, cefazolin is recommended for intrapartum prophylaxis 1
Clinical Pitfalls to Avoid
Do not confuse treatment of GBS UTI with prevention of neonatal GBS disease—these require completely different approaches. 1
- GBS UTI in non-pregnant women can be treated with nitrofurantoin like other uncomplicated UTIs 2, 6
- GBS bacteriuria during pregnancy requires documentation for intrapartum prophylaxis planning, not immediate antibiotic treatment 1
- Never use nitrofurantoin for systemic GBS infections, bacteremia, or any infection outside the bladder 2
- Avoid nitrofurantoin in elderly patients with reduced renal function, as serious adverse effects including pulmonary reactions and polyneuropathy are more common with impaired kidney function 2, 3