Bactrim Dosing for Pediatric UTI
For pediatric urinary tract infections, administer trimethoprim-sulfamethoxazole at 6-12 mg/kg/day of the trimethoprim component (with 30-60 mg/kg/day sulfamethoxazole) divided into 2 doses daily for 7-14 days. 1, 2
Standard Dosing Regimen
- The FDA-approved dosing is 8 mg/kg trimethoprim with 40 mg/kg sulfamethoxazole per 24 hours, divided every 12 hours for 10-14 days 3
- The American Academy of Pediatrics recommends a slightly broader range of 6-12 mg/kg trimethoprim with 30-60 mg/kg sulfamethoxazole per day in 2 divided doses 1, 2
- Bactrim should not be used in infants less than 2 months of age 3
Weight-Based Dosing Table
For practical dosing using standard tablets (400 mg sulfamethoxazole/80 mg trimethoprim), the FDA provides the following guidance 3:
- 22 lb (10 kg): 1 tablet every 12 hours
- 44 lb (20 kg): 1½ tablets every 12 hours
- 66 lb (30 kg): 2 tablets every 12 hours (or 1 double-strength tablet)
- 88 lb (40 kg): 2 tablets every 12 hours (or 1 double-strength tablet)
Treatment Duration
- The total course should be 7-14 days for UTI treatment 1, 2, 4
- Shorter courses of 1-3 days are inferior to the recommended 7-14 day range, particularly for febrile UTIs 1
- Single-dose trimethoprim, while effective at clearing initial bacteriuria, results in significantly higher recurrence rates (23% vs 2%) compared to standard 7-10 day courses 5
Route of Administration
- Most children with UTI can be treated orally 1, 2, 4
- Switch to parenteral therapy if the child appears "toxic," cannot retain oral intake, or has compliance concerns 1, 2, 4
Critical Prescribing Considerations
Local Resistance Patterns
- Always consider local antimicrobial susceptibility patterns before prescribing, as geographic variability in trimethoprim-sulfamethoxazole resistance is substantial 2, 4
- Adjust therapy based on culture and sensitivity results when available 1
Febrile UTI/Pyelonephritis Considerations
- Trimethoprim-sulfamethoxazole is appropriate for febrile UTIs, unlike nitrofurantoin which does not achieve adequate serum and parenchymal concentrations 1, 4
- For severe pyelonephritis requiring parenteral therapy, use ceftriaxone 50-75 mg/kg/day or cefotaxime 150 mg/kg/day instead 4
Monitoring Requirements
- Perform complete blood counts 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
Common Pitfalls to Avoid
- Do not use treatment durations less than 7 days for febrile UTIs, as this leads to treatment failure 1
- Do not prescribe if local E. coli resistance rates to trimethoprim-sulfamethoxazole are high 2, 4
- Do not use in infants under 2 months of age 3
- Do not use nitrofurantoin instead for febrile UTIs or suspected pyelonephritis 1, 4
Renal Impairment Dosing
For patients with impaired renal function 3:
- Creatinine clearance >30 mL/min: Use usual standard regimen
- Creatinine clearance 15-30 mL/min: Use half the usual regimen
- Creatinine clearance <15 mL/min: Use not recommended