What are safe antibiotic options for a pregnant woman with a urinary tract infection (UTI)?

Safe Antibiotics for Pregnant Women with UTI

Nitrofurantoin (100 mg twice daily for 5-7 days) is the first-line antibiotic for UTI in pregnancy, with cephalexin (500 mg four times daily for 7-14 days) as the preferred alternative, particularly in the third trimester or for suspected pyelonephritis. 1, 2

First-Line Treatment Options

Nitrofurantoin

• Nitrofurantoin is recommended as first-line therapy across all trimesters with a dosing regimen of 100 mg twice daily for 5-7 days 2
• This agent has an excellent safety profile with extremely low rates of serious adverse events: pulmonary toxicity occurs in only 0.001% and hepatic toxicity in 0.0003% of cases 2
• Critical caveat: Do not use nitrofurantoin for suspected pyelonephritis as it does not achieve therapeutic blood concentrations needed for upper tract infections 1
• Nitrofurantoin should be avoided near term (after 38 weeks) due to theoretical risk of neonatal hemolysis 1

Cephalosporins

• Cephalexin is the preferred cephalosporin at 500 mg four times daily for 7-14 days, particularly valuable as a first-line alternative in the third trimester 1
• Other appropriate cephalosporins include cefpodoxime and cefuroxime, all achieving adequate blood and urinary concentrations with excellent pregnancy safety profiles 1
• Third-generation cephalosporins like cefixime are also effective options given high sensitivity of E. coli and proven safety in pregnancy 3

Fosfomycin

• Fosfomycin trometamol (single 3g dose) is an acceptable alternative for uncomplicated lower UTI, though clinical data for third trimester use is more limited than for cephalosporins 1, 2
• This single-dose option offers excellent compliance for uncomplicated cystitis 2

Second-Line Options

Amoxicillin-Clavulanate

• Amoxicillin-clavulanate (20-40 mg/kg per day in 3 divided doses) is appropriate if the pathogen is susceptible 1
• Reproduction studies in mice and rats at doses up to 2000 mg/kg showed no evidence of fetal harm, though amoxicillin should be used only if clearly needed 4

Trimethoprim-Sulfamethoxazole (Limited Use)

• Avoid in the first trimester due to potential interference with folic acid metabolism and theoretical risk of neural tube defects 2
• Contraindicated in the third trimester due to risk of neonatal hyperbilirubinemia and kernicterus 1, 2
• May be used in the second trimester (160/800 mg twice daily for 3-7 days) when other options are unsuitable 2

Antibiotics to Absolutely Avoid

• Fluoroquinolones (ciprofloxacin, levofloxacin) are contraindicated throughout pregnancy due to potential adverse effects on fetal cartilage development and arthropathy demonstrated in juvenile animals 1

Treatment Duration and Follow-Up

• Standard treatment course is 7-14 days to ensure complete eradication, though 5-7 days may be acceptable for uncomplicated lower UTI with certain agents 1, 2
• Single-dose therapy shows higher failure rates compared to multi-day courses 2
• Obtain urine culture before initiating treatment to guide antibiotic selection, as pyuria screening alone has only 50% sensitivity for identifying bacteriuria 1, 2
• Perform follow-up urine culture 1-2 weeks after completing treatment to confirm cure 1

Critical Clinical Context

• Untreated bacteriuria increases pyelonephritis risk 20-30 fold (from 1-4% with treatment to 20-35% without treatment) 1
• Treatment reduces premature delivery and low birth weight infants 1
• Pregnancy is the one clinical scenario where asymptomatic bacteriuria must always be treated due to significant risk for progression to pyelonephritis and adverse pregnancy outcomes 1, 2
• Screen all pregnant women with urine culture at 12-16 weeks gestation 2

Management of Pyelonephritis

• For severe infections or pyelonephritis, initial parenteral therapy with second or third-generation cephalosporins is required during hospitalization, with transition to oral therapy after clinical improvement 1, 5
• Cephalosporins achieve adequate blood concentrations necessary for upper tract infections, unlike nitrofurantoin 1

Special Considerations

• For recurrent UTIs, consider prophylactic cephalexin for the remainder of pregnancy 1
• If Group B Streptococcus is isolated in any concentration, treat at diagnosis and provide intrapartum prophylaxis during labor to prevent neonatal sepsis 1
• Antibiotic choice should consider local resistance patterns, as E. coli resistance to ampicillin is high and this agent should not be used 5