Why is nitrofurantoin (antibiotic) avoided in urinary tract infections (UTIs) during the last trimester of pregnancy and what alternative antibiotics can be used?

Nitrofurantoin in Third Trimester UTIs: Contraindications and Alternatives

Nitrofurantoin should be avoided in the third trimester of pregnancy due to the risk of hemolytic anemia in the newborn, particularly in those with G6PD deficiency, and should be replaced with safer alternatives such as cephalosporins.

Why Nitrofurantoin is Avoided in Third Trimester

• Nitrofurantoin is contraindicated in the third trimester (after 36 weeks) due to the risk of hemolytic anemia in the newborn, especially in infants with glucose-6-phosphate dehydrogenase (G6PD) deficiency 1
• The medication can cause oxidative stress in red blood cells which may lead to hemolysis when the baby is exposed near delivery 2
• While nitrofurantoin is generally considered safe during the first and second trimesters, its use should be restricted in late pregnancy 3

Alternative Antibiotics for Third Trimester UTIs

First-Line Alternatives

• Cephalosporins (such as cephalexin, cefpodoxime, or cefuroxime) are the preferred first-line alternatives for treating UTIs in the third trimester 2
  • Typical dosing: Cephalexin 500 mg four times daily for 7-14 days 4
  • These medications achieve adequate blood and urinary concentrations and have excellent safety profiles in pregnancy 4

Other Safe Options

• Amoxicillin-clavulanate (20-40 mg/kg per day in 3 doses) is an appropriate alternative if the pathogen is susceptible 4
• Fosfomycin (single 3g dose) can be considered for uncomplicated lower UTIs, though clinical data for third trimester use is more limited than for cephalosporins 4, 2

Medications to Avoid

• Fluoroquinolones (such as ciprofloxacin) should be avoided throughout pregnancy due to potential adverse effects on fetal cartilage development 2
• Trimethoprim-sulfamethoxazole should be avoided in late pregnancy due to the risk of kernicterus and hyperbilirubinemia in the newborn 5, 1

Treatment Duration and Approach

• The total course of therapy should be 7-14 days to ensure complete eradication of the infection 4, 2
• For suspected pyelonephritis, initial parenteral therapy may be required with transition to oral therapy after clinical improvement 2
• A urine culture should always be obtained before initiating treatment to guide therapy 4

Special Considerations

• Asymptomatic bacteriuria in pregnancy should always be treated to prevent progression to pyelonephritis and adverse pregnancy outcomes 4
• Women with Group B Streptococcus bacteriuria during pregnancy require treatment at diagnosis and intrapartum prophylaxis during labor 2
• Follow-up urine culture 1-2 weeks after completing treatment is recommended to confirm cure 4

Clinical Algorithm for UTI Treatment in Third Trimester

1. Obtain urine culture before starting antibiotics 4
2. Start empiric therapy with cephalexin 500 mg four times daily 4, 2
3. Adjust therapy based on culture results and susceptibility testing 4
4. Complete a 7-14 day course of antibiotics 4
5. Perform follow-up urine culture 1-2 weeks after treatment 4
6. For recurrent UTIs, consider prophylactic antibiotics (cephalexin) for the remainder of pregnancy 4

Remember that untreated UTIs in pregnancy can lead to pyelonephritis, preterm labor, low birth weight, and sepsis, so prompt and appropriate treatment is essential 4.