What is the recommended treatment for a urinary tract infection (UTI) in a pregnant patient?

Treatment of Urinary Tract Infections in Pregnancy

For pregnant women with UTI, obtain a urine culture before initiating treatment and prescribe nitrofurantoin (50-100 mg four times daily for 7 days) as first-line therapy, with cephalexin (500 mg four times daily for 7-14 days) or fosfomycin (3g single dose) as appropriate alternatives. 1, 2

Screening and Diagnosis

• All pregnant women should be screened for asymptomatic bacteriuria at 12-16 weeks gestation using urine culture, as this is the only clinical scenario where asymptomatic bacteriuria must always be treated 3, 1, 2
• Dipstick testing for pyuria alone has only 50% sensitivity and is inadequate for diagnosis—urine culture is mandatory 1, 2
• Untreated bacteriuria increases pyelonephritis risk from 1-4% (with treatment) to 20-35% (without treatment), representing a 20-30 fold increase 1, 2
• Treatment reduces premature delivery and low birth weight infants 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, 2
• Fosfomycin trometamol (3g single dose) is an acceptable alternative 1, 2
• Cephalosporins (cephalexin, cefpodoxime, cefuroxime) are appropriate alternatives with excellent safety profiles 1, 2
• Avoid trimethoprim-sulfamethoxazole in the first trimester due to potential teratogenic effects including anencephaly, heart defects, and orofacial clefts 1, 4

Second Trimester

• Same options as first trimester: nitrofurantoin, fosfomycin, or cephalosporins 1, 2

Third Trimester

• Cephalexin becomes the preferred agent (500 mg four times daily for 7-14 days) 1
• Avoid nitrofurantoin near term as it does not achieve therapeutic blood concentrations needed for systemic infections 1
• Fosfomycin (3g single dose) can be considered for uncomplicated lower UTIs 1
• Amoxicillin-clavulanate (20-40 mg/kg per day in 3 doses) if pathogen is susceptible 1

Antibiotics to Avoid Throughout Pregnancy

• Fluoroquinolones (ciprofloxacin, levofloxacin) should be avoided throughout all trimesters due to potential adverse effects on fetal cartilage development and arthropathy in juvenile animals 1, 4, 5
• Trimethoprim-sulfamethoxazole is contraindicated in the first and third trimesters 1, 6
• Tetracyclines should be avoided 2

Treatment Duration

• The recommended treatment duration is 7-14 days for symptomatic UTI, though the optimal duration remains uncertain 3, 1, 2
• For asymptomatic bacteriuria, the IDSA recommends 4-7 days of antimicrobial treatment rather than shorter durations 3
• Single-dose therapy showed a trend toward lower clearance rates compared to 4-7 day courses 3
• Fosfomycin as a single 3g dose is effective for uncomplicated lower UTIs 1, 2

Special Considerations for Pyelonephritis

• Agents that do not achieve therapeutic blood concentrations, such as nitrofurantoin, should never be used for suspected pyelonephritis 1
• Initial parenteral therapy may be required for severe infections, with transition to oral therapy after clinical improvement 1
• Cephalosporins achieve adequate blood and urinary concentrations and are preferred for upper tract infections 1

Group B Streptococcus (GBS) Bacteriuria

• GBS bacteriuria in any concentration during pregnancy is a marker for heavy genital tract colonization and requires treatment at diagnosis 1
• Women with GBS bacteriuria also require intrapartum GBS prophylaxis during labor 1

Post-Treatment Follow-Up

• Repeat urine culture 1-2 weeks after completing treatment is essential to confirm eradication 1, 2
• For recurrent UTIs, consider prophylactic antibiotics (cephalexin) for the remainder of pregnancy 1
• There is insufficient evidence to recommend routine repeat screening during pregnancy for women with an initial negative culture 3

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 treat asymptomatic bacteriuria repeatedly after the initial screen-and-treat approach, as this fosters antimicrobial resistance 1
• Do not rely on dipstick testing alone—always obtain urine culture before initiating treatment 1, 2
• Do not use nitrofurantoin for pyelonephritis or near term 1

Penicillin Allergy Considerations

• 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 remain safe options 1