Nitrofurantoin (Macrobid) for GBS UTI in Pregnancy
Nitrofurantoin is NOT recommended as first-line therapy for Group B Streptococcus UTI in pregnant women—penicillin G or ampicillin should be used instead, followed by mandatory intrapartum IV antibiotic prophylaxis during labor regardless of earlier treatment. 1
Why Penicillin-Based Antibiotics Are Preferred
- GBS displays 100% susceptibility to penicillin, making it the most reliable choice for eradicating this pathogen 2
- The American College of Obstetricians and Gynecologists recommends penicillin G (5 million units IV initially, then 2.5 million units IV every 4 hours) as the preferred agent for GBS treatment in pregnancy due to its narrow spectrum of activity and high efficacy 1
- Ampicillin (2 g IV initial dose, then 1 g IV every 4 hours) is an acceptable alternative for inpatient treatment 1
Nitrofurantoin's Limited Role
- While nitrofurantoin shows activity against GBS in vitro (with only 2% of isolates showing intermediate sensitivity), it is not the recommended first-line agent for GBS UTI 3
- Nitrofurantoin is effective for treating uncomplicated UTIs caused by E. coli and other common uropathogens, but GBS requires targeted therapy with beta-lactam antibiotics 2, 4
- One study suggested "patients with GBS bacteriuria should be treated with nitrofurantoin," but this contradicts current CDC and ACOG guidelines that prioritize penicillin-based therapy 3
Critical Management Requirements for GBS Bacteriuria in Pregnancy
- Any concentration of GBS in urine during pregnancy requires immediate treatment AND intrapartum IV prophylaxis during labor, regardless of whether the UTI was treated earlier 1, 5
- GBS bacteriuria indicates heavy genital tract colonization and significantly increases the risk of early-onset neonatal GBS disease 1, 5
- Treating the acute UTI does NOT eliminate GBS colonization—recolonization after oral antibiotics is typical, which is why intrapartum IV prophylaxis remains mandatory 1
Treatment Algorithm for Pregnant Women with GBS UTI
For immediate UTI treatment:
- First-line: Penicillin-based antibiotics (penicillin G or ampicillin) 1
- Penicillin allergy (not high-risk): Cefazolin 2 g IV initially, then 1 g IV every 8 hours 1
- Penicillin allergy (high-risk for anaphylaxis): Clindamycin 900 mg IV every 8 hours (if susceptible) or vancomycin 1 g IV every 12 hours 1
For intrapartum prophylaxis during labor:
- Penicillin G 5 million units IV initially, then 2.5 million units IV every 4 hours until delivery 1
- Alternative: Ampicillin 2 g IV initially, then 1 g IV every 4 hours until delivery 1
- Prophylaxis must be administered ≥4 hours before delivery for maximum effectiveness (78% reduction in early-onset neonatal GBS disease) 1
Common Pitfalls to Avoid
- Do not assume that treating the UTI with any antibiotic eliminates the need for intrapartum prophylaxis—this is a dangerous error 1
- Do not use nitrofurantoin after 36 weeks gestation due to risk of neonatal hemolysis 6
- Do not screen for GBS colonization at 35-37 weeks if GBS bacteriuria was already documented—the patient is presumed heavily colonized and automatically qualifies for intrapartum prophylaxis 1
- Ensure laboratory reports of GBS bacteriuria are communicated to both the anticipated site of delivery and the ordering provider 1