What is the recommended treatment for a pregnant woman with an Escherichia coli (E. coli) urinary tract infection (UTI)?

Treatment of E. coli UTI in Pregnant Women

Pregnant women with E. coli UTI should be treated with nitrofurantoin (50-100 mg four times daily for 5-7 days) or a single 3-gram dose of fosfomycin as first-line therapy, with cephalosporins (such as cephalexin 500 mg four times daily for 7-14 days) as appropriate alternatives. 1

Diagnostic Approach

Always obtain a urine culture before initiating treatment to guide antibiotic selection and confirm the diagnosis, as screening for pyuria alone has only 50% sensitivity for identifying bacteriuria in pregnant women. 1, 2

• All pregnant women should be screened for asymptomatic bacteriuria with urine culture at 12-16 weeks gestation or at the first prenatal visit if later. 3
• Pregnancy is the one clinical scenario where asymptomatic bacteriuria must always be treated due to 20-30 fold increased risk of pyelonephritis (from 1-4% with treatment to 20-35% without treatment). 3, 1, 2
• Treatment of bacteriuria reduces premature delivery and low birth weight infants. 3, 1

First-Line Antibiotic Options by Trimester

First Trimester

• Nitrofurantoin is the preferred first-line agent (50-100 mg four times daily for 5-7 days). 1
• Fosfomycin trometamol is an acceptable alternative (single 3-gram dose). 1
• Avoid trimethoprim-sulfamethoxazole in the first trimester due to potential teratogenic effects. 1

Second Trimester

• Nitrofurantoin and fosfomycin remain appropriate options. 1
• Cephalosporins (cephalexin, cefpodoxime, or cefuroxime) are safe and effective alternatives. 1

Third Trimester

• Cephalexin 500 mg four times daily for 7-14 days is the preferred alternative to nitrofurantoin. 1
• Nitrofurantoin should be avoided near term due to theoretical risk of hemolytic anemia in the newborn. 1
• Amoxicillin-clavulanate (20-40 mg/kg per day in 3 doses) is appropriate if the pathogen is susceptible. 1
• Fosfomycin (single 3g dose) can be considered for uncomplicated lower UTIs, though clinical data for third trimester use is more limited. 1

Treatment Duration

The recommended duration is 4-7 days for asymptomatic bacteriuria and 7-14 days for symptomatic UTI, with the shortest effective course preferred depending on the antimicrobial chosen. 3, 1

• Despite insufficient evidence comparing shorter regimens, 7-14 day courses are recommended as Cochrane reviews found inadequate data to support single-dose, 3-day, or 4-day regimens over 7-day courses. 1

Antibiotics to Avoid Throughout Pregnancy

Fluoroquinolones (such as ciprofloxacin) must be avoided throughout pregnancy due to potential adverse effects on fetal cartilage development, despite animal studies showing no teratogenicity. 1

• Trimethoprim-sulfamethoxazole should be avoided in the first trimester and is contraindicated in the last trimester. 1

Treatment of Pyelonephritis in Pregnancy

For pregnant women with pyelonephritis requiring hospitalization:

• Initial parenteral therapy with ceftriaxone (1-2g daily) or cefepime (1-2g twice daily) is recommended. 1
• Transition to oral cephalosporin therapy after clinical improvement for completion of 7-14 day course. 1
• Do not use nitrofurantoin for pyelonephritis, as it does not achieve therapeutic concentrations in the bloodstream. 1
• An aminoglycoside with or without ampicillin, extended-spectrum cephalosporin, or carbapenem are alternatives based on local resistance data. 3

Follow-Up and Monitoring

• Obtain follow-up urine culture 1-2 weeks after completing treatment to confirm cure. 1
• Periodic screening for recurrent bacteriuria should be undertaken following therapy. 2
• Do not perform surveillance urine testing or treat asymptomatic bacteriuria repeatedly after the initial screen-and-treat approach, as this fosters antimicrobial resistance. 1
• For recurrent UTIs, consider prophylactic antibiotics (cephalexin) for the remainder of pregnancy. 1

Special Considerations for Penicillin Allergy

• Despite theoretical cross-reactivity concerns, only 10% of penicillin-allergic patients have reactions to cephalosporins. 1
• Assess whether the patient is at high risk for anaphylaxis; if not, cephalosporins are safe. 1
• Nitrofurantoin or fosfomycin remain excellent alternatives for patients with true penicillin allergy. 1

Critical Pitfalls to Avoid

• Do not classify pregnant women with UTIs as "complicated" unless they have structural/functional urinary tract abnormalities or immunosuppression, as this leads to unnecessary broad-spectrum antibiotic use. 1
• Do not delay treatment in pregnant women with symptomatic UTI, as this increases the risk of pyelonephritis and adverse pregnancy outcomes. 1
• Do not rely on pyuria alone for diagnosis without urine culture confirmation. 2
• Antibiotic choice must consider local resistance patterns and patient-specific factors such as allergies. 1