What are the best antibiotics for treating urinary tract infections (UTI) in pregnancy?

Best Antibiotics for UTI in Pregnancy

Nitrofurantoin or cephalexin are recommended as first-line treatments for UTIs in pregnancy, with ampicillin being the first choice for asymptomatic bacteriuria. 1

First-Line Treatment Options

The American College of Obstetricians and Gynecologists recommends the following antibiotics for UTI treatment during pregnancy:

1. Nitrofurantoin - 100 mg twice daily for 5 days 1

   • High strength of evidence
   • Safe and effective during pregnancy
   • Should be avoided in the third trimester due to risk of hemolytic anemia in G6PD-deficient infants

2. Cephalexin - 500 mg four times daily for 5-7 days 1

   • Moderate strength of evidence
   • Safe throughout pregnancy

3. Ampicillin - 2g IV initial dose, then 1g IV every 4 hours until delivery 1

   • Particularly recommended for asymptomatic bacteriuria
   • Effective against E. coli, the most common UTI pathogen in pregnancy

Second-Line Options

• Amoxicillin-clavulanate - 500/125 mg twice daily for 3-7 days 1

  • Moderate strength of evidence
  • Safe during pregnancy but may cause gastrointestinal side effects

• Fosfomycin - 3g single dose 1, 2

  • Moderate strength of evidence
  • Convenient single-dose regimen
  • Studies show comparable efficacy to nitrofurantoin 2

Antibiotics to Avoid or Use with Caution

• Trimethoprim-sulfamethoxazole 1, 3

  • Should be avoided in first trimester (risk of neural tube defects)
  • Should be avoided in third trimester (risk of kernicterus)
  • ACOG recommends using only when other antimicrobials are clinically inappropriate 3

• Fluoroquinolones (e.g., ciprofloxacin) 1, 3

  • Should be reserved as last resort
  • High resistance rates
  • Potential for adverse effects

• Tetracyclines 1

  • Contraindicated throughout pregnancy
  • Can cause harm to fetal bone and teeth development

Treatment Duration and Follow-up

• For uncomplicated UTIs, a treatment duration of 3-7 days is typically sufficient 1
• For asymptomatic bacteriuria, the same antibiotics can be used but treatment is essential to prevent complications 1
• Urine culture should be repeated 7 days after completing therapy to confirm cure 4

Prevention of Recurrent UTIs in Pregnancy

For women with history of recurrent UTIs during pregnancy:

• Postcoital prophylaxis with either:

  • Cephalexin (250 mg) single dose after intercourse 5
  • Nitrofurantoin macrocrystals (50 mg) single dose after intercourse 5
  • Highly effective in preventing recurrence 5

• Other preventive measures:

  • Increased fluid intake
  • Good urogenital hygiene
  • Regular and complete bladder emptying 1

Clinical Considerations

• Screen for asymptomatic bacteriuria in all pregnant women, as untreated bacteriuria can lead to pyelonephritis, preterm labor, and low birth weight 1, 3
• Consider local resistance patterns when selecting antibiotics
• Be aware that amoxicillin may affect oral contraceptives by reducing their efficacy 6
• Monitor renal function when using antibiotics excreted primarily by the kidneys 6
• Be cautious with amoxicillin in patients also taking allopurinol due to increased risk of rash 6

Despite the availability of multiple antibiotics for UTI treatment in pregnancy, the evidence base for specific regimens is surprisingly limited 7. However, the safety profile and efficacy data strongly support nitrofurantoin and cephalexin as first-line agents, with ampicillin being preferred for asymptomatic bacteriuria.