What is the best antibiotic for pregnant women with a urinary tract infection (UTI)?

Best Antibiotics for UTI in Pregnant Women

Nitrofurantoin is the recommended first-line antibiotic for pregnant women with uncomplicated urinary tract infections, followed by fosfomycin as an alternative first-line option. 1

First-Line Options

Nitrofurantoin

• Highly effective against common uropathogens with 97.8% susceptibility for E. coli 1
• Safety profile in pregnancy is well-established through retrospective analyses 2
• No significant difference in adverse fetal outcomes compared to the general population 2
• Typically prescribed as 100 mg twice daily for 5 days 3
• Caution: Should be used with care in the first trimester due to potential risk for birth defects 4

Fosfomycin

• Single 300 mg oral dose provides excellent coverage (100% susceptibility for E. coli) 1
• Comparable clinical and microbiological cure rates to nitrofurantoin 3
• Particularly useful for pregnant women due to single-dose administration improving compliance 3
• Safe option for asymptomatic bacteriuria in pregnancy 3

Second-Line Options

Cephalexin

• Frequently prescribed during pregnancy for UTIs 4
• Good option when first-line agents are contraindicated
• Broader spectrum coverage than nitrofurantoin

Trimethoprim-Sulfamethoxazole (TMP-SMX)

• Should be avoided in the first trimester due to potential risk for birth defects 4
• May be considered in later pregnancy if pathogen is resistant to first-line options
• Cure rates of greater than 80% have been reported 5

Treatment Algorithm

1. First trimester UTI:

   • Fosfomycin 3g single dose (preferred)
   • Cephalexin if fosfomycin unavailable/contraindicated
   • Avoid nitrofurantoin and TMP-SMX if possible due to potential birth defect risks 4

2. Second and third trimester UTI:

   • Nitrofurantoin 100mg twice daily for 5 days
   • Fosfomycin 3g single dose (alternative)
   • Cephalexin or TMP-SMX if pathogens resistant to first-line options

3. Pyelonephritis or complicated UTI:

   • Hospitalization may be required
   • Parenteral antibiotics until clinically improved
   • Complete 7-14 days of appropriate antibiotics

Important Considerations

• UTIs occur in approximately 8% of pregnant women and are most common in the third trimester 4, 1
• Untreated UTIs can lead to serious complications including pyelonephritis, preterm labor, low birth weight, and sepsis 4
• E. coli is the predominant pathogen in UTIs during pregnancy 1
• Obtain urine culture before initiating antibiotics to guide therapy
• Follow-up urine culture 7 days after treatment to confirm cure 5
• Asymptomatic bacteriuria should be treated in pregnancy to prevent complications 5

Common Pitfalls to Avoid

• Using fluoroquinolones (e.g., ciprofloxacin) during pregnancy due to potential risks to fetal cartilage development
• Failing to obtain follow-up cultures to confirm cure
• Not considering local antibiogram patterns when selecting empiric therapy
• Undertreating UTIs in pregnancy, which can lead to serious maternal and fetal complications
• Using prolonged courses of antibiotics when shorter durations are equally effective