What is the recommended treatment for a 21-week pregnant woman diagnosed with a urinary tract infection (UTI)?

Treatment of UTI at 21 Weeks Pregnancy

Start nitrofurantoin 100 mg orally twice daily for 7-14 days immediately after obtaining a urine culture. 1, 2

Immediate Diagnostic Steps

• Obtain a urine culture before starting antibiotics to guide therapy and confirm the diagnosis 2
• Do not wait for culture results to initiate treatment—start empirical therapy immediately given symptomatic UTI 2
• Pyuria alone has only 50% sensitivity for identifying bacteriuria, making urine culture essential 1, 2

First-Line Antibiotic: Nitrofurantoin

Nitrofurantoin is the preferred first-line agent for UTI at 21 weeks gestation (second trimester), with excellent safety profile and efficacy 1, 2

• Dosing: 100 mg orally twice daily for 7-14 days 2
• Reduces pyelonephritis risk from 20-35% to 1-4% 2
• Achieves adequate urinary concentrations with minimal teratogenic risk 2

Critical Caveat About Nitrofurantoin

• Do NOT use nitrofurantoin if pyelonephritis is suspected—it does not achieve therapeutic blood concentrations needed for upper tract infections 1

Alternative First-Line Options

If nitrofurantoin cannot be used, choose from these alternatives:

• Cephalexin 500 mg four times daily for 7-14 days (preferred alternative with excellent safety profile and adequate blood/urinary concentrations) 1, 2
• Fosfomycin 3g single oral dose (acceptable alternative, though clinical data for second trimester is more limited than cephalosporins) 1, 3
• Cefpodoxime or cefuroxime for 7-14 days (appropriate cephalosporin alternatives) 1

Antibiotics to AVOID at 21 Weeks

• Fluoroquinolones (ciprofloxacin, levofloxacin): Contraindicated throughout pregnancy due to potential adverse effects on fetal cartilage development 1, 2
• Trimethoprim-sulfamethoxazole: Should be avoided in second trimester when possible, though less critical than in first or third trimester 1

Treatment Duration Rationale

• 7-14 day courses are recommended despite insufficient evidence comparing shorter regimens 1, 2
• Cochrane reviews found inadequate data to support single-dose, 3-day, or 4-day regimens over 7-day courses 1
• The goal is complete eradication to prevent progression to pyelonephritis 1

Essential Follow-Up

• Perform follow-up urine culture 1-2 weeks after completing treatment to confirm bacteriologic cure 1, 2
• Do NOT perform repeated surveillance testing or treat asymptomatic bacteriuria after initial treatment, as this fosters antimicrobial resistance 1

Clinical Context: Why Treatment is Urgent

• Untreated bacteriuria increases pyelonephritis risk 20-30 fold (from 1-4% with treatment to 20-35% without) 1, 2
• Treatment reduces premature delivery and low birth weight infants 1
• Even asymptomatic bacteriuria must be treated during pregnancy due to significant risk for adverse outcomes 1, 2

Special Consideration: Group B Streptococcus

• If GBS is identified in the urine culture at any concentration, this indicates heavy genital tract colonization 1
• Treat the UTI at time of diagnosis AND provide intrapartum GBS prophylaxis during labor 1

If Severe Infection or Pyelonephritis Develops

• Initial parenteral therapy may be required (third-generation cephalosporins or amoxicillin with aminoglycoside) 1, 4
• Transition to oral therapy after clinical improvement 1
• Consider hospitalization for severe cases 4