What is the correct dose of Bactrim (trimethoprim/sulfamethoxazole) for pediatric urinary tract infections (UTIs)?

Correct Dosage of Trimethoprim/Sulfamethoxazole for Pediatric UTI

For pediatric urinary tract infections, trimethoprim/sulfamethoxazole should be dosed at 6-12 mg/kg trimethoprim and 30-60 mg/kg sulfamethoxazole per day divided into 2 doses. 1

Dosing Guidelines

• The FDA-approved dosage for children with urinary tract infections is 8 mg/kg trimethoprim and 40 mg/kg sulfamethoxazole per 24 hours, given in two divided doses every 12 hours 2
• The American Academy of Pediatrics recommends 6-12 mg/kg trimethoprim and 30-60 mg/kg sulfamethoxazole per day in 2 doses for pediatric UTI treatment 1
• This medication is not recommended for infants less than 2 months of age 2

Treatment Duration

• The total course of therapy should be 7 to 14 days 1
• Evidence shows that shorter courses (1-3 days) are inferior to the recommended 7-14 day range for febrile UTIs 1
• While single-dose regimens have shown effectiveness in clearing bacteria initially, they are associated with higher rates of recurrence (23%) compared to standard courses (2%) 3

Route of Administration

• Most children with UTI can be treated orally 1
• Parenteral administration should be considered for children who:
  • Appear "toxic" 1
  • Are unable to retain oral intake including medications 1
  • Have compliance concerns with oral administration 1

Special Considerations

• Local antimicrobial susceptibility patterns should guide empiric therapy choice 1
• Adjust therapy based on culture and sensitivity results when available 1
• For febrile infants with UTI, avoid nitrofurantoin as it does not achieve adequate serum and parenchymal concentrations to treat pyelonephritis 1
• Monitor for adverse effects:
  • Complete blood counts should be performed at initiation of treatment and monthly for long-term therapy 1
  • If serious adverse reactions occur (anaphylaxis, Stevens-Johnson syndrome), permanently discontinue the medication 1

Weight-Based Dosing Guide

For children 2 months and older with UTI 2:

• 22 lb (10 kg): 1 regular strength tablet (400 mg/80 mg) every 12 hours
• 44 lb (20 kg): 2 regular strength tablets or 1 double strength tablet every 12 hours
• 66 lb (30 kg): 3 regular strength tablets or 1.5 double strength tablets every 12 hours

Common Pitfalls

• Using inadequate treatment duration (less than 7 days) for febrile UTIs may lead to treatment failure 1
• Failing to adjust therapy based on local resistance patterns can result in treatment failure 1
• Using nitrofurantoin for febrile UTIs or pyelonephritis is inappropriate as it doesn't achieve adequate tissue concentrations 1
• Not considering renal function when dosing TMP-SMX can lead to toxicity in patients with impaired renal function 2