What is the recommended treatment for a urinary tract infection (UTI) in the 3rd trimester of pregnancy?

Treatment of Urinary Tract Infections in the 3rd Trimester of Pregnancy

For urinary tract infections during the 3rd trimester of pregnancy, second-generation cephalosporins are the recommended first-line empiric treatment to ensure optimal clinical and microbiological cure rates while minimizing risks to mother and fetus. 1

Diagnostic Considerations

• Obtain urine culture before initiating antibiotics to confirm diagnosis and guide targeted therapy 1
• Significant bacteriuria is defined as ≥50,000 CFUs/mL of a single urinary pathogen 2
• Document symptoms and assess severity to determine appropriate treatment setting (outpatient vs. inpatient) 1

Treatment Algorithm

First-Line Treatment Options:

• Second-generation cephalosporins (e.g., cefuroxime) are recommended as first-line empiric therapy 1
• Dosing for oral cefuroxime axetil: 20-30 mg/kg per day in 2 doses 2

Second-Line Treatment Options:

• Aminoglycosides (e.g., gentamicin) may be used as second-line therapy in 2nd and 3rd trimester when benefits outweigh risks 1
• Dosing for parenteral gentamicin: 7.5 mg/kg per day, divided every 8 hours 2

Third-Line Treatment Options:

• Third-generation cephalosporins (e.g., ceftriaxone, cefotaxime) should be used as third-line options due to risk of inducing antimicrobial resistance 1
• Dosing for parenteral ceftriaxone: 75 mg/kg, every 24 hours 2
• Dosing for parenteral cefotaxime: 150 mg/kg per day, divided every 6-8 hours 2

Alternative Options:

• Amoxicillin-clavulanate can be used for beta-lactamase-producing E. coli, Klebsiella species, and Enterobacter species 3
• Oral dosing: 20-40 mg/kg per day in 3 doses 2

Treatment Duration and Monitoring

• Total course of therapy should be 7-10 days for uncomplicated UTIs 1
• For hospitalized patients with upper UTIs, switch to oral therapy after at least 48 hours of clinical improvement and adequate oral intake 1
• Obtain follow-up urine culture 7 days after completing therapy to confirm cure 4

Special Considerations

Severity Assessment

• Initial management of upper UTIs (pyelonephritis) should be in a hospital setting 1
• Patients who are "toxic" or unable to retain oral intake should receive parenteral antibiotics initially 2
• Switch to oral therapy after resolution of systemic inflammatory response (typically 48 hours) 1

Antibiotic Selection Caveats

• Avoid nitrofurantoin for treatment of pyelonephritis as it doesn't achieve adequate serum concentrations 2
• Adjust antibiotic therapy based on culture and sensitivity results when available 1
• For patients with history of infections caused by resistant organisms, carbapenems are suggested as first-line therapy 1

Common Pitfalls to Avoid

• Do not use trimethoprim-sulfamethoxazole in the third trimester due to risk of neonatal hyperbilirubinemia and kernicterus 5
• Avoid prolonged use of aminoglycosides due to potential ototoxicity and nephrotoxicity risks 1
• Do not delay treatment of symptomatic UTIs as they can lead to serious maternal and fetal complications including preterm delivery and low birth weight 5, 6

By following this treatment algorithm for UTIs in the third trimester, clinicians can effectively manage infections while minimizing risks to both mother and fetus.