What is the best empiric antibiotic for a pregnant woman with a urinary tract infection (UTI) caused by Escherichia coli (E. coli) and an allergy to penicillins (penicillin-class antibiotics)?

Best Empiric Antibiotic for Pregnant Woman with E. coli UTI and Penicillin Allergy

For a 32-year-old pregnant woman with UTI positive for E. coli and penicillin allergy, nitrofurantoin is the best empiric antibiotic choice while awaiting sensitivities. 1, 2

First-Line Options for Pregnant Women with UTI

• Nitrofurantoin is highly effective against E. coli (79-99% sensitivity) and has a good safety profile in pregnancy, making it an excellent first-line choice for uncomplicated lower UTIs in pregnant women with penicillin allergy 1, 2, 3

• E. coli is the most common causative organism in UTIs during pregnancy, accounting for approximately 75-86% of cases 1, 4, 2

• WHO Essential Medicines guidelines specifically recommend nitrofurantoin as a first-choice option for lower UTIs, with maintained high susceptibility patterns against urinary E. coli isolates 1

Alternative Options Based on Infection Severity

• For patients with signs of upper UTI (pyelonephritis) or systemic symptoms, ceftriaxone is recommended as it maintains good activity against E. coli (>90% susceptibility) and is generally safe in penicillin-allergic patients unless they have a history of anaphylaxis to penicillins 4, 5

• If the patient has a history of anaphylaxis, angioedema, respiratory distress, or urticaria with penicillins, avoid cephalosporins and consider:

  • Fosfomycin (if available) - highly effective against E. coli (98-99% sensitivity) and safe in pregnancy 2
  • Gentamicin - can be considered in the second and third trimesters if other options aren't suitable 5

Important Clinical Considerations

• Pregnancy is considered a complicating factor for UTIs, increasing the risk of progression to pyelonephritis and potential adverse pregnancy outcomes 1

• Obtain a urine culture before starting antibiotics, but don't delay treatment while awaiting results 1, 5

• Adjust therapy based on culture and sensitivity results when they become available 5

• Treatment duration for uncomplicated lower UTI should be 5-7 days; for upper UTI (pyelonephritis), 7-10 days is recommended 1, 5

• Avoid fluoroquinolones (ciprofloxacin) during pregnancy due to potential fetal risks, despite their effectiveness against E. coli 1, 6

• Trimethoprim-sulfamethoxazole should be avoided in the first trimester (risk of neural tube defects) and near term (risk of neonatal hyperbilirubinemia) 6

Antibiotic Resistance Considerations

• E. coli resistance to commonly used antibiotics is increasing globally, with high resistance rates to ampicillin (65-95%), amoxicillin-clavulanate (17-73%), and trimethoprim-sulfamethoxazole (65-96%) 4, 3

• Nitrofurantoin maintains good activity against most E. coli strains, with resistance rates generally remaining low (5-20%) 4, 3

• Local antibiogram data should guide therapy whenever possible, as resistance patterns vary geographically 1