Pediatric Dosing of Trimethoprim-Sulfamethoxazole
For routine pediatric infections, administer 8 mg/kg/day trimethoprim with 40 mg/kg/day sulfamethoxazole divided every 12 hours; for severe infections and PCP treatment, use 15–20 mg/kg/day trimethoprim with 75–100 mg/kg/day sulfamethoxazole divided every 6 hours; for PCP prophylaxis, give 150 mg/m²/day trimethoprim with 750 mg/m²/day sulfamethoxazole divided twice daily on 3 consecutive days per week. 1
Routine Infections (UTI, Otitis Media, Shigellosis)
Oral Dosing
- Administer 8 mg/kg trimethoprim + 40 mg/kg sulfamethoxazole per 24 hours, divided into 2 doses every 12 hours. 1
- Duration: 10 days for UTI/otitis media, 5 days for shigellosis. 1
- Contraindicated in infants <2 months of age. 1
Weight-Based Tablet Dosing Guide
- 10–20 kg: 1 single-strength tablet every 12 hours 1
- 30 kg: 1½ single-strength tablets every 12 hours 1
- 40 kg: 2 single-strength tablets (or 1 double-strength tablet) every 12 hours 1
Severe Infections and Skin/Soft Tissue Infections
MRSA Skin Infections (Purulent Cellulitis)
- Oral dosing: Trimethoprim 4–6 mg/kg/dose + sulfamethoxazole 20–30 mg/kg/dose every 12 hours. 2
- This represents a moderate-intensity regimen between routine and PCP treatment dosing. 2
- Avoid in third-trimester pregnancy and children <2 months. 2
Intravenous Administration for Complicated Infections
- The FDA label provides oral dosing guidance but does not specify distinct IV pediatric dosing for routine infections. 1
- For severe infections requiring IV therapy, follow PCP treatment dosing principles (see below) and adjust based on clinical severity. 1
Pneumocystis Jirovecii Pneumonia (PCP)
Treatment Dosing
- 15–20 mg/kg/day trimethoprim + 75–100 mg/kg/day sulfamethoxazole, divided into 4 doses every 6 hours. 1
- Duration: 14–21 days. 1
- Both oral and IV routes achieve similar serum levels and can be used interchangeably. 3
Weight-Based Treatment Guide (Upper Limit Dosing)
- 8–16 kg: 1 single-strength tablet every 6 hours 1
- 24 kg: 1½ single-strength tablets every 6 hours 1
- 32 kg: 2 single-strength tablets (or 1 double-strength) every 6 hours 1
- 40 kg: 2½ single-strength tablets every 6 hours 1
- 48 kg: 3 single-strength tablets (or 1½ double-strength) every 6 hours 1
- For lower limit dosing (15 mg/kg trimethoprim), administer 75% of the above doses. 1
PCP Prophylaxis
- 150 mg/m²/day trimethoprim + 750 mg/m²/day sulfamethoxazole, divided every 12 hours, given on 3 consecutive days per week. 1, 2
- Maximum daily dose: 320 mg trimethoprim + 1600 mg sulfamethoxazole. 1
Body Surface Area Dosing Guide for Prophylaxis
- 0.26–0.53 m²: ½ single-strength tablet every 12 hours (on designated days) 1
- 1.06 m²: 1 single-strength tablet every 12 hours (on designated days) 1
Critical Dosing Considerations
Renal Impairment
- Creatinine clearance 15–30 mL/min: Reduce dose to 50% of usual regimen. 1
- Creatinine clearance <15 mL/min: Use not recommended. 1
- Trimethoprim clearance inversely correlates with serum creatinine in children. 4
Pharmacokinetic Pitfalls
- Serum levels accumulate over 4–6 days despite loading doses, with trough concentrations rising 63% for trimethoprim and 102% for sulfamethoxazole. 3
- Large interindividual variability occurs despite weight-based dosing, particularly in high-dose regimens. 3
- Trimethoprim clearance increases with age; younger children (<6 years) may require higher mg/kg doses to match adult exposures. 4
Safety Monitoring
- Thrombocytopenia is the most common cause of discontinuation (37% of cases), particularly in patients ≥50 years, lymphocyte count <1000/μL, or baseline platelet count <180,000/μL. 5
- Monitor complete blood counts regularly, especially during prolonged therapy. 5
- Transient neutropenia may occur but often resolves spontaneously. 6