Macrobid (Nitrofurantoin) for Mixed E. coli and Group B Strep UTI
Nitrofurantoin is NOT adequate for this patient because it lacks reliable activity against Streptococcus agalactiae (Group B Strep), despite being highly effective against E. coli. You must select an alternative antibiotic that covers both organisms.
Why Nitrofurantoin Fails Here
- Nitrofurantoin has excellent activity against E. coli (98.1% susceptibility among resistant isolates) and is recommended as first-line therapy for uncomplicated cystitis 1, 2
- However, nitrofurantoin does NOT reliably cover Group B Streptococcus - this organism is not listed among pathogens for which nitrofurantoin demonstrates consistent activity 3
- Group B Strep requires beta-lactam antibiotics - all GBS strains show 100% sensitivity to penicillin, ampicillin, and vancomycin 4
Critical Pregnancy Consideration
If this patient is pregnant or could be pregnant, this becomes urgent:
- Screen and treat immediately - pregnant women should be screened for and treated for bacteriuria to prevent pyelonephritis and adverse pregnancy outcomes 1
- GBS bacteriuria in pregnancy indicates heavy colonization and requires treatment plus intrapartum antibiotic prophylaxis to prevent neonatal sepsis 4
- Nitrofurantoin is contraindicated in the last trimester of pregnancy 3
Recommended Antibiotic Choices
For symptomatic UTI with E. coli + GBS, use:
- Ampicillin or amoxicillin - provides complete coverage of both organisms, with GBS showing 100% susceptibility 4
- Amoxicillin-clavulanate - broader coverage if concerned about beta-lactamase producing E. coli 2
- First-generation cephalosporin (cephalexin) - alternative if penicillin allergy is not severe 1
Duration:
If Patient is NOT Pregnant and Asymptomatic
- Do not treat asymptomatic bacteriuria in non-pregnant women, even with positive cultures 1
- Strong recommendation against screening or treating ASB in healthy premenopausal non-pregnant women 1
- Treatment causes harm through adverse effects, costs, and antimicrobial resistance without preventing symptomatic UTI 1
Clinical Algorithm
- Determine if patient has symptoms (dysuria, frequency, urgency, suprapubic pain) 1
- Assess pregnancy status immediately - urine pregnancy test if any possibility 1
- If symptomatic OR pregnant: Treat with ampicillin/amoxicillin or amoxicillin-clavulanate for 5-7 days 1, 4
- If asymptomatic AND not pregnant: Do not treat 1
Common Pitfall to Avoid
Do not reflexively prescribe nitrofurantoin just because it's "first-line" for UTI - this only applies to typical E. coli cystitis 1. When you have documented GBS, you must adjust therapy to cover all identified organisms 4. The 23-34% of women with GBS UTIs are at higher risk and require appropriate beta-lactam coverage 4.