What medication is safe to treat a urinary tract infection (UTI) in a pregnant woman?

Safe Antibiotics for UTI Treatment in Pregnancy

Nitrofurantoin (50-100 mg four times daily for 5-7 days) and cephalosporins (such as cephalexin 500 mg four times daily for 7-14 days) are the safest first-line antibiotics for treating UTIs during pregnancy, with fosfomycin (3g single dose) as an acceptable alternative. 1

First-Line Treatment Options by Trimester

First Trimester

• Nitrofurantoin is the preferred first-line agent for lower UTI treatment during the first trimester 1
• Fosfomycin trometamol (3g single dose) serves as an acceptable alternative to nitrofurantoin 1
• Cephalosporins (cephalexin, cefpodoxime, cefuroxime) are appropriate options throughout pregnancy with excellent safety profiles 1
• Avoid trimethoprim-sulfamethoxazole in the first trimester due to potential teratogenic effects including neural tube defects 1, 2

Second and Third Trimesters

• Cephalexin 500 mg four times daily for 7-14 days is the recommended first-line alternative for third trimester UTIs, particularly when nitrofurantoin should be avoided near term 1
• Amoxicillin-clavulanate (20-40 mg/kg per day in 3 doses) is appropriate if the pathogen is susceptible 1
• Trimethoprim-sulfamethoxazole is contraindicated in the last trimester due to risk of kernicterus 1

Critical Antibiotics to Avoid

• Fluoroquinolones (ciprofloxacin, levofloxacin) must be avoided throughout pregnancy due to potential adverse effects on fetal cartilage development and arthropathy 1, 3
• Nitrofurantoin should not be used for pyelonephritis as it does not achieve therapeutic blood concentrations 1
• Nitrofurantoin should be avoided near term (after 38 weeks) due to theoretical risk of hemolytic anemia in the newborn 1

Treatment Duration and Monitoring

• Standard treatment duration is 7-14 days for symptomatic UTI to ensure complete eradication 1
• Obtain urine culture before initiating treatment to guide antibiotic selection, as screening for pyuria alone has only 50% sensitivity 1
• Perform follow-up urine culture 1-2 weeks after completing treatment to confirm cure 1
• Screen for asymptomatic bacteriuria at 12-16 weeks gestation with urine culture 1

Treatment of Pyelonephritis in Pregnancy

• Cephalosporins and fluoroquinolones are recommended for oral empiric treatment of uncomplicated pyelonephritis in non-pregnant patients, but fluoroquinolones must be avoided in pregnancy 4
• Initial parenteral therapy with ceftriaxone (1-2g daily) or cefepime (1-2g twice daily) is appropriate for hospitalized pregnant women with pyelonephritis 4
• Transition to oral cephalosporin therapy after clinical improvement for completion of 7-14 day course 1

Asymptomatic Bacteriuria Management

• All pregnant women with asymptomatic bacteriuria must be treated as untreated bacteriuria increases pyelonephritis risk 20-30 fold (from 1-4% with treatment to 20-35% without) 1
• Treatment reduces premature delivery and low birth weight infants 1
• Do not perform repeated surveillance testing or treat asymptomatic bacteriuria multiple times after the initial screen-and-treat approach, as this fosters antimicrobial resistance 1

Special Considerations

• Group B Streptococcus (GBS) bacteriuria in any concentration requires treatment at diagnosis plus intrapartum prophylaxis during labor 1
• For recurrent UTIs, consider prophylactic cephalexin for the remainder of pregnancy 1
• Postcoital prophylaxis with cephalexin 250 mg or nitrofurantoin 50 mg is highly effective for pregnant women with history of recurrent UTIs 5

Common 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 rely on pyuria alone for diagnosis, as it has only 50% sensitivity for bacteriuria 1
• Do not use single-dose or 3-day regimens, as insufficient evidence supports shorter courses compared to 7-14 day regimens 1
• Antibiotic choice must consider local resistance patterns, as ampicillin and amoxicillin are associated with high E. coli resistance rates 6