What is a safe medication for a urinary tract infection (UTI) in a pregnant patient?

Safe Antibiotics for UTI in Pregnancy

For pregnant patients with UTIs, nitrofurantoin (100 mg twice daily for 5-7 days) is the first-line treatment during the first and second trimesters, while cephalexin (500 mg four times daily for 7-14 days) is preferred in the third trimester and for any suspected pyelonephritis. 1

First-Line Treatment by Trimester

First and Second Trimester

• Nitrofurantoin (50-100 mg four times daily for 5-7 days) is the primary recommendation from European Urology guidelines for symptomatic UTI 1
• Fosfomycin trometamol (3g single dose) serves as an acceptable alternative with comparable efficacy 1
• Cephalosporins (cephalexin, cefpodoxime, or cefuroxime) are appropriate alternatives with excellent safety profiles throughout pregnancy 1

Third Trimester

• Cephalexin (500 mg four times daily for 7-14 days) becomes the preferred first-line agent 1
• Nitrofurantoin should be avoided near term due to theoretical risk of hemolytic anemia in the newborn 2
• Amoxicillin-clavulanate (20-40 mg/kg per day in 3 doses) is appropriate if the pathogen is susceptible 1

Critical Antibiotics to Avoid

Throughout Pregnancy

• Fluoroquinolones (ciprofloxacin, levofloxacin) must be avoided due to potential adverse effects on fetal cartilage development 1
• Despite being commonly prescribed (second most frequent in 2014 data), ciprofloxacin carries significant fetal risks 3

Trimester-Specific Restrictions

• Trimethoprim-sulfamethoxazole should be avoided in the first trimester due to teratogenic effects (anencephaly, heart defects, orofacial clefts) and is contraindicated in the third trimester 1, 3

Treatment Duration and Monitoring

Standard Course

• 7-14 days for symptomatic UTI to ensure complete eradication 1
• 4-7 days may be acceptable for asymptomatic bacteriuria, though 7-day courses are generally preferred 1
• Single-dose fosfomycin provides effective treatment for uncomplicated lower UTIs 1

Essential Follow-Up

• Obtain urine culture before initiating treatment to guide antibiotic selection 1
• Perform follow-up urine culture 1-2 weeks after completing treatment to confirm cure 1
• Optimal screening timing is at 12-16 weeks gestation with a single urine culture 1

Special Clinical Scenarios

Pyelonephritis (Upper UTI)

• Never use nitrofurantoin for suspected pyelonephritis as it doesn't achieve therapeutic blood concentrations 1
• Initial parenteral therapy with ceftriaxone (1-2g daily) or cefepime (1-2g twice daily) for hospitalized patients 1
• Transition to oral cephalosporin after clinical improvement for completion of 7-14 day course 1

Asymptomatic Bacteriuria

• Must always be treated during pregnancy - this is the one clinical exception where asymptomatic bacteriuria requires treatment 1
• Untreated bacteriuria increases pyelonephritis risk 20-30 fold (from 1-4% to 20-35%) 1
• Treatment reduces premature delivery and low birth weight infants 1

Group B Streptococcus (GBS) Bacteriuria

• Any concentration of GBS bacteriuria during pregnancy indicates heavy genital tract colonization 1
• Requires treatment at diagnosis plus intrapartum GBS prophylaxis during labor 1

Recurrent UTIs

• Consider prophylactic cephalexin for the remainder of pregnancy after multiple episodes 1
• Postcoital prophylaxis with cephalexin (250 mg) or nitrofurantoin (50 mg) is highly effective 4

Common Pitfalls to Avoid

Diagnostic Errors

• Do not rely on pyuria alone - it has only 50% sensitivity for identifying bacteriuria in pregnancy 1
• Always obtain urine culture; screening for pyuria is inadequate 1

Treatment Errors

• Do not use nitrofurantoin for pyelonephritis - look for fever, flank pain, or systemic symptoms suggesting upper tract involvement 1
• Do not perform surveillance urine testing after initial treatment unless symptoms recur, as this fosters antimicrobial resistance 1
• Do not use amoxicillin or ampicillin alone for empirical treatment due to high resistance rates 2

Prescribing Considerations

• Despite ACOG 2011 recommendations to limit nitrofurantoin in the first trimester, it remains the guideline-recommended first-line agent based on risk-benefit analysis 1, 3
• The theoretical risks are outweighed by the proven benefits of treating UTIs and preventing pyelonephritis 1

Antibiotic Safety Profile Summary

Pregnancy Category B (Safe)

• Nitrofurantoin (except near term) 1
• Cephalosporins (all trimesters) 1
• Fosfomycin 1
• Amoxicillin-clavulanate 5

Clinical Context

The urgency of treatment cannot be overstated: untreated UTIs lead to a 20-30 fold increase in pyelonephritis risk, with associated premature delivery, low birth weight, and potential sepsis 1. Implementation of screening programs decreased pyelonephritis rates from 1.8-2.1% to 0.5-0.6%, demonstrating the critical importance of early detection and appropriate treatment 1.