What is the recommended treatment for a urinary tract infection (UTI) in a 6-month-old child?

Treatment of UTI in a 6-Month-Old Child

A 6-month-old with a UTI should be treated with oral antibiotics for 7-14 days if well-appearing and able to retain oral intake, with first-line options including cefixime (8 mg/kg/day once daily), cephalexin (50-100 mg/kg/day divided into 4 doses), or amoxicillin-clavulanate (20-40 mg/kg/day divided into 3 doses), based on local resistance patterns. 1, 2, 3, 4

Initial Assessment and Route of Administration

Determine if parenteral therapy is needed:

• Reserve IV/IM antibiotics for infants who appear toxic, cannot retain oral medications, or have uncertain compliance 1, 2
• Well-appearing 6-month-olds who can tolerate oral intake can be treated entirely with oral antibiotics, as oral and parenteral routes are equally efficacious 2
• If parenteral therapy is needed, use ceftriaxone 50 mg/kg IV/IM every 24 hours, then transition to oral antibiotics once the infant is clinically improved 2, 5

First-Line Oral Antibiotic Options

Choose based on local resistance patterns:

• Cefixime: 8 mg/kg/day as a single daily dose (FDA-approved for infants ≥6 months with UTI) 1, 2, 4
• Cephalexin: 50-100 mg/kg/day divided into 4 doses 1, 3
• Amoxicillin-clavulanate: 20-40 mg/kg/day divided into 3 doses 1, 3
• Trimethoprim-sulfamethoxazole: Only if local E. coli resistance is <10% (6-12 mg/kg trimethoprim component per day in 2 divided doses) 2, 3

Treatment Duration

Complete 7-14 days of total antibiotic therapy:

• The most commonly supported duration is 10 days for febrile UTI 2
• Shorter courses (1-3 days) are inferior and should never be used 1, 3
• Early treatment within 48 hours of fever onset reduces risk of renal scarring by >50% 2

Critical Pitfalls to Avoid

Do NOT use nitrofurantoin in this age group:

• Nitrofurantoin does not achieve adequate serum/tissue concentrations to treat pyelonephritis in febrile infants 1, 3

Always obtain urine culture before starting antibiotics:

• Use catheterization or suprapubic aspiration for collection—never use bag specimens for culture 2, 3
• Diagnosis requires both pyuria AND ≥50,000 CFU/mL of a single uropathogen 2, 3

Imaging Recommendations

Obtain renal and bladder ultrasound (RBUS):

• All febrile infants <2 years with first UTI should have RBUS to detect anatomic abnormalities 1, 2, 3
• Ultrasound is the only study that is usually appropriate (rated 9/9 by ACR) 6
• Perform when patient is well-hydrated with distended bladder 2

Voiding cystourethrography (VCUG) is NOT routinely needed:

• VCUG should only be performed if RBUS shows hydronephrosis, scarring, or findings suggesting high-grade VUR/obstruction, OR after a second febrile UTI 1, 2, 3
• In boys <2 months, consider VCUG due to higher prevalence of VUR and to exclude posterior urethral valves 6

Follow-Up Strategy

Reassess within 1-2 days:

• Confirm fever resolution and clinical improvement within 24-48 hours of starting antibiotics 1, 2
• If fever persists beyond 48 hours despite appropriate therapy, this constitutes an "atypical" UTI requiring further evaluation including imaging 6, 1

No routine scheduled visits after successful treatment:

• Instruct parents to seek prompt evaluation (within 48 hours) for any future febrile illness to detect recurrent UTI early 1, 2

Adjust Therapy Based on Culture Results

Modify antibiotics when sensitivities are available:

• Consider local antibiotic resistance patterns when selecting empiric therapy 1, 2, 3
• E. coli accounts for approximately 85% of pediatric UTIs 7
• Extended-spectrum β-lactamase producing E. coli (E-ESBL) rates are 7-10% in pediatrics; if suspected, consider amikacin as initial therapy 8