Macrobid Should NOT Be Used for Group B Strep in Pregnancy
Macrobid (nitrofurantoin) is not recommended for treating Group B streptococcus (GBS) colonization in pregnant women, and antimicrobial agents should not be used before the intrapartum period to treat asymptomatic GBS colonization at all. 1
Why Treatment Before Labor Doesn't Work
The evidence clearly demonstrates that prenatal treatment of GBS colonization is ineffective:
Administering antimicrobial agents to pregnant women before the onset of labor or rupture of membranes is not likely to prevent neonatal GBS disease. 1
In studies where colonized pregnant women received oral antimicrobial drugs for 1 week during the third trimester, more than 30% were still colonized at delivery, with no substantial difference between treated and untreated groups. 1
Even with 12-14 days of treatment during the third trimester (including treatment of sex partners), nearly 70% of colonized women remained colonized 3 weeks later and again at delivery. 1
Colonization status can change between treatment and delivery, making prenatal treatment ineffective. 2
The Correct Approach: Intrapartum Prophylaxis
Intrapartum chemoprophylaxis (administration of antimicrobial agents after onset of labor or membrane rupture but before delivery) is the most likely method of preventing both early-onset disease and maternal illness resulting from GBS. 1
First-Line Agents
Penicillin remains the first-line agent for intrapartum antibiotic prophylaxis, with ampicillin an acceptable alternative. 1
All GBS isolates in multiple studies showed 100% sensitivity to penicillin G, ampicillin, and vancomycin. 3
Alternative Agents for Penicillin Allergy
Cefazolin is recommended for prophylaxis in women without significant penicillin allergy. 4
Clindamycin and vancomycin are reserved for cases of significant maternal penicillin allergy. 4
Pregnant women with a history of penicillin allergy should undergo skin testing, as confirmation or delabeling can provide both short- and long-term health benefits. 4
What About Nitrofurantoin Specifically?
While one study found no GBS strains resistant to nitrofurantoin 5, this does not make it appropriate for GBS prophylaxis because:
The CDC guidelines explicitly state that antimicrobial agents should not be used before the intrapartum period to treat asymptomatic GBS colonization. 1, 2
Nitrofurantoin is not listed among recommended intrapartum prophylaxis regimens in any guideline. 1, 4, 6
The timing of administration (intrapartum) and the specific agents used (penicillin/ampicillin) are critical to effectiveness.
Screening and Timing
Universal prenatal culture-based screening for vaginal and rectal GBS colonization should occur at 36 0/7 to 37 6/7 weeks' gestation (updated from the previous 35-37 weeks window). 4, 6
Women with GBS bacteriuria at any concentration during pregnancy require intrapartum antibiotic prophylaxis regardless of screening results, as this indicates heavy colonization. 1, 2
Critical Caveat
For non-pregnant women, GBS vaginal colonization requires no treatment whatsoever. 2, 7 Treatment is only indicated for symptomatic urinary tract infections or invasive infections, not asymptomatic colonization. 2, 7