What is the best antibiotic for a pregnant woman with a urinary tract infection (UTI)?

Best Antibiotic for UTI in Pregnancy

Cephalexin 500 mg four times daily for 7-14 days is the best first-line antibiotic for treating UTI in pregnancy, with nitrofurantoin as an alternative for uncomplicated lower UTI in the first trimester only. 1, 2

First-Line Treatment by Trimester

First Trimester

• Nitrofurantoin is the preferred first-line agent for uncomplicated lower UTI during the first trimester 1, 2
• Fosfomycin (single 3g dose) is an acceptable alternative for uncomplicated lower UTI, though clinical data is more limited 1, 2
• Cephalosporins (cephalexin, cefpodoxime, cefuroxime) are safe and effective alternatives that achieve adequate blood and urinary concentrations 1, 2

Second and Third Trimesters (≥20 weeks)

• Cephalexin 500 mg four times daily for 7-14 days is recommended as first-line therapy 1, 2
• Avoid nitrofurantoin at ≥20 weeks gestation, especially if pyelonephritis is suspected or there are concerns for upper tract involvement, as it does not achieve therapeutic blood concentrations 1, 2
• Alternative cephalosporins (cefpodoxime, cefuroxime) are equally effective with excellent safety profiles 1, 2
• Amoxicillin-clavulanate can be used if the pathogen is susceptible, though cephalosporins are preferred 2

Antibiotics to Absolutely Avoid

• Trimethoprim-sulfamethoxazole should never be used, particularly in the first trimester, due to teratogenic effects 1, 2
• Fluoroquinolones (ciprofloxacin, levofloxacin) are contraindicated throughout pregnancy due to adverse effects on fetal cartilage development 1, 2

Critical Management Steps

Before Treatment

• Always obtain urine culture before initiating antibiotics to guide therapy and allow adjustment if the organism is resistant 1, 2
• Optimal screening timing is at 12-16 weeks gestation 2
• Screening for pyuria alone has only 50% sensitivity and is inadequate 2

Treatment Duration

• 7-14 day courses are required for complete eradication 1, 2
• Single-dose or 3-day regimens are insufficient and associated with higher bacteriological persistence 3

After Treatment

• Repeat urine culture 1-2 weeks after completing treatment is mandatory to confirm eradication 1, 2
• Untreated or incompletely treated UTI can progress to pyelonephritis in 20-35% of cases without treatment versus 1-4% with treatment 2

Special Clinical Scenarios

Asymptomatic Bacteriuria

• Pregnancy is the one exception where asymptomatic bacteriuria must always be treated 3, 2
• Treatment reduces pyelonephritis risk 20-30 fold and decreases premature delivery and low birth weight 2

Suspected Pyelonephritis

• Hospitalization with IV ceftriaxone or cefepime is required if fever, flank pain, nausea/vomiting are present 1
• Never use nitrofurantoin for suspected upper tract involvement 1, 2

Recurrent UTI

• Consider prophylactic cephalexin for the remainder of pregnancy after recurrent infections 1, 2
• Post-coital prophylaxis with cephalexin 250 mg or nitrofurantoin 50 mg is highly effective, reducing 130 UTIs to a single UTI during pregnancy 4

Group B Streptococcus (GBS) Bacteriuria

• Any concentration of GBS bacteriuria requires treatment at diagnosis plus intrapartum prophylaxis during labor 2

Common Pitfalls to Avoid

• Do not use nitrofurantoin after 20 weeks gestation or for any suspected pyelonephritis - it lacks adequate blood concentrations 1, 2
• Do not skip the post-treatment urine culture - this is essential to confirm cure and prevent progression to pyelonephritis 1, 2
• Do not use shorter courses (<7 days) - insufficient evidence supports their efficacy and they increase treatment failure 3, 2
• Do not delay treatment - even asymptomatic bacteriuria carries significant risk for adverse pregnancy outcomes 2