What is the safe treatment for a pregnant woman with a urinary tract infection (UTI)?

Safe Treatment of UTI in Pregnancy

Nitrofurantoin 100 mg orally four times daily for 5-7 days is the first-line treatment for urinary tract infections in pregnant women, with cephalexin 500 mg orally four times daily for 7-14 days as an alternative. 1

Essential Pre-Treatment Steps

• Obtain a urine culture before initiating antibiotics to guide antibiotic selection and confirm diagnosis 1
• Screen for asymptomatic bacteriuria at 12-16 weeks gestation, as untreated bacteriuria increases pyelonephritis risk from 1-4% to 20-37% 1
• Any concentration of Group B Streptococcus requires immediate treatment regardless of colony count 1

First-Line Antibiotic Options

For Uncomplicated Cystitis:

• Nitrofurantoin 100 mg orally four times daily for 5-7 days (preferred) 1
• Cephalexin 500 mg orally four times daily for 7-14 days (alternative) 1
• Fosfomycin 3 g single dose for uncomplicated cystitis 1

The evidence strongly supports these agents due to their safety profile in pregnancy and effectiveness against common uropathogens, particularly E. coli which accounts for >75% of UTIs 2. Nitrofurantoin has been used safely for over 35 years with continuing safety record and lack of resistance development 3.

Treatment Duration:

• Minimum 4-7 days for symptomatic UTI and asymptomatic bacteriuria 1
• 7-14 day total course with cephalosporins ensures complete eradication 1

This differs from non-pregnant women where 3-5 day courses are standard 2, reflecting the higher stakes of incomplete treatment during pregnancy.

Second-Line Options

• Cefuroxime or amoxicillin-clavulanate for 7 days 4
• Amoxicillin and other cephalosporins may be used but have higher therapeutic failure rates 4
• Third-generation cephalosporins like cefixime show high sensitivity against E. coli 5

Critical Post-Treatment Monitoring

• Repeat urine culture 1-2 weeks after completing treatment to confirm microbiological cure 1
• Failure to confirm cure leads to missed persistent infections that dramatically increase pyelonephritis risk 1

Severe Infections/Pyelonephritis

• Initial parenteral therapy is required for severe infections or pyelonephritis 1
• Hospitalization is typically necessary given significant maternal and fetal risks 1

Antibiotics to AVOID in Pregnancy

• Trimethoprim-sulfamethoxazole is contraindicated in first trimester (neural tube defects) and last trimester (kernicterus risk) 1
• Fluoroquinolones should be avoided due to concerns about fetal cartilage development 1

This is a critical distinction from non-pregnant women where TMP-SMX and fluoroquinolones are first-line agents 2.

Prophylaxis for Recurrent UTI in Pregnancy

For women with history of recurrent UTIs:

• Cephalexin 250-500 mg as continuous or postcoital prophylaxis 4
• Nitrofurantoin 100 mg (contraindicated after 37 weeks gestation) 4
• Postcoital prophylaxis with single oral dose of cephalexin 250 mg or nitrofurantoin 50 mg is highly effective, reducing UTI incidence from 130 infections pre-prophylaxis to only 1 infection during pregnancy 6

Common Pitfalls to Avoid

• Never treat without obtaining urine culture first - this is essential for confirming diagnosis and guiding therapy 1
• Never skip post-treatment culture - failure to confirm cure is a major cause of ascending infection 1
• Never use nitrofurantoin after 37 weeks gestation due to hemolytic anemia risk in newborns 4
• Never assume asymptomatic bacteriuria is benign in pregnancy - it requires treatment unlike in non-pregnant women 2, 1