What are safe antibiotic options for a pregnant woman in her 2nd trimester with a urinary tract infection (UTI)?

Safe UTI Medications in the Second Trimester

Cephalosporins, specifically cephalexin 500 mg four times daily for 7-14 days, are the first-line treatment for UTIs in the second trimester of pregnancy. 1, 2

Primary Treatment Options

First-Line: Cephalosporins

• Cephalexin is the preferred agent, achieving adequate blood and urinary concentrations with an excellent safety profile throughout pregnancy. 1, 2
• Alternative cephalosporins include cefpodoxime, cefuroxime, or cefixime, all of which are appropriate options with similar safety profiles. 1, 2, 3
• The total treatment course should be 7-14 days to ensure complete eradication of the infection. 1, 2

Second-Line: Nitrofurantoin

• Nitrofurantoin (50-100 mg four times daily for 5-7 days) is safe and effective for uncomplicated lower UTIs in the second trimester. 1, 4
• However, nitrofurantoin should NOT be used if pyelonephritis is suspected or if there are any signs of upper tract involvement (fever, flank pain, nausea/vomiting), as it does not achieve therapeutic concentrations in the bloodstream. 1, 2

Third-Line: Fosfomycin

• Fosfomycin trometamol (single 3g dose) can be considered for uncomplicated lower UTIs, though clinical data for second trimester use is more limited compared to cephalosporins. 1, 2, 4

Fourth-Line: Amoxicillin-Clavulanate

• Amoxicillin-clavulanate is an appropriate alternative if the pathogen is susceptible based on culture results. 1
• The FDA label confirms no evidence of fetal harm in animal studies at doses up to 2000 mg/kg, though it should be used only if clearly needed. 5

Antibiotics to AVOID in Second Trimester

• Trimethoprim-sulfamethoxazole should be avoided due to potential teratogenic effects, particularly concerns about neural tube defects and other birth defects. 1, 2, 6
• Fluoroquinolones (ciprofloxacin, levofloxacin) must be avoided throughout all trimesters due to adverse effects on fetal cartilage development and arthropathy risk. 1, 2
• Ampicillin should not be used due to high resistance rates to E. coli, the most common uropathogen. 7

Essential Management Steps

Before Treatment

• Always obtain a urine culture before initiating empirical antibiotic therapy to guide subsequent treatment adjustments if the organism is resistant. 1, 2, 8
• Assess for signs of upper tract involvement (fever >38°C, flank pain, costovertebral angle tenderness, nausea/vomiting) to distinguish cystitis from pyelonephritis. 2

After Treatment

• Perform a follow-up urine culture 1-2 weeks after completing treatment to confirm eradication, as untreated or incompletely treated UTI can progress to pyelonephritis. 1, 2
• Do not perform repeated surveillance testing or treat asymptomatic bacteriuria multiple times after the initial screen-and-treat approach, as this fosters antimicrobial resistance. 1

Special Considerations for Pyelonephritis

If upper tract infection is suspected in the second trimester:

• Hospitalization with initial IV therapy is required using ceftriaxone or cefepime as first-line agents. 2, 8
• Second-generation cephalosporins are preferred for empirical management to improve clinical and microbiological cure rates. 8
• After at least 48 hours of clinical improvement and adequate oral tolerance, switch to oral therapy to complete 7-10 days total. 8

Critical Clinical Context

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

Common Pitfalls to Avoid

• Do not use nitrofurantoin for suspected pyelonephritis or any signs suggesting upper tract involvement. 1, 2
• Do not prescribe fluoroquinolones despite their effectiveness in non-pregnant patients—the fetal risks outweigh benefits. 1, 2
• Do not skip the pre-treatment urine culture, as empirical therapy may need adjustment based on resistance patterns. 1, 2, 8
• Do not use single-dose or 3-day regimens—insufficient evidence supports shorter courses in pregnancy. 1