Septran (Trimethoprim-Sulfamethoxazole) Pediatric Dosing
For pediatric patients ≥2 months of age, the standard treatment dose is 8 mg/kg/day of trimethoprim (40 mg/kg/day of sulfamethoxazole) divided into two doses every 12 hours. 1, 2
Treatment Dosing by Indication
Urinary Tract Infections, Acute Otitis Media, and Shigellosis
- Dose: 8 mg/kg trimethoprim + 40 mg/kg sulfamethoxazole per 24 hours, divided every 12 hours 1, 2
- Duration: 10 days for UTI/otitis media; 5 days for shigellosis 1, 2
- Weight-based dosing table (per dose every 12 hours): 1, 2
- 10-20 kg: 1 single-strength tablet (80/400 mg)
- 30 kg: 1½ single-strength tablets
- 40 kg: 2 single-strength tablets OR 1 double-strength tablet
Skin and Soft Tissue Infections (including MRSA)
- Dose: 8-12 mg/kg/day of trimethoprim divided every 12 hours 3
- Duration: 7-10 days 3
- The CDC recommends 5 mg/kg (trimethoprim component) every 12 hours as an alternative dosing approach 4
Pneumocystis jirovecii Pneumonia (PCP)
Treatment:
- Dose: 15-20 mg/kg trimethoprim + 75-100 mg/kg sulfamethoxazole per 24 hours, divided every 6 hours 1, 2
- Duration: 14-21 days 1, 2
Prophylaxis:
- Dose: 150 mg/m²/day trimethoprim + 750 mg/m²/day sulfamethoxazole, divided every 12 hours 1, 2
- Schedule: 3 consecutive days per week (alternative to daily dosing) 5
- Maximum daily dose: 320 mg trimethoprim + 1600 mg sulfamethoxazole 1, 2
- The CDC also recommends 8 mg/kg/day trimethoprim divided into two doses for prophylaxis 5
Critical Age Restriction
Septran is absolutely contraindicated in infants <2 months of age due to risk of kernicterus. 3, 1, 2
Renal Dose Adjustment
For patients with impaired renal function: 1, 2
- CrCl >30 mL/min: Standard dosing
- CrCl 15-30 mL/min: Reduce dose by 50%
- CrCl <15 mL/min: Avoid use
Monitoring Requirements
- Baseline: Complete blood count with differential and platelet count before initiating therapy 5, 3
- Ongoing: Monthly CBC for prolonged therapy or prophylaxis to detect hematologic toxicity 4, 5, 3
Important Clinical Caveats
Formulation Considerations
- For accurate dosing in younger children or those <40 kg, liquid formulation is preferred over tablets 5
- Liquid suspension typically contains 40 mg trimethoprim + 200 mg sulfamethoxazole per 5 mL
Common Pitfalls to Avoid
- Do not confuse the trimethoprim and sulfamethoxazole components when calculating doses—always base calculations on the trimethoprim component 4, 3
- Do not use in G6PD deficiency due to risk of hemolytic anemia 3
- Exercise caution with concurrent methotrexate as toxicity may increase 3
Serious Adverse Effects Requiring Discontinuation
- Stevens-Johnson syndrome or toxic epidermal necrolysis 4
- Severe blood dyscrasias 4
- Hepatic necrosis 4
- Life-threatening hypersensitivity reactions 5