Sulfatrim (Trimethoprim-Sulfamethoxazole) Pediatric Dosing
For most infections in children over 2 months of age, administer 8-12 mg/kg/day of trimethoprim (TMP) with 40-60 mg/kg/day of sulfamethoxazole (SMX), divided into 2 doses given every 12 hours. 1
Standard Treatment Dosing by Indication
Mild-to-Moderate Infections (UTI, Skin/Soft Tissue)
- 8-10 mg/kg/day of TMP component divided every 12 hours 1
- This translates to 40-50 mg/kg/day of SMX 1
- Duration: 10-14 days for UTI, 5 days for shigellosis 2
Serious Infections (Severe MRSA)
- 10-12 mg/kg/day of TMP component divided every 12 hours 1
- For life-threatening infections: up to 15-20 mg/kg/day of TMP divided every 6-8 hours 1
- For severe MRSA osteomyelitis specifically: 4 mg/kg/dose of TMP every 8-12 hours, typically combined with rifampin for >6 weeks 1
Pneumocystis Jirovecii Pneumonia (PCP)
Treatment:
- 15-20 mg/kg/day of TMP with 75-100 mg/kg/day of SMX, divided into 4 doses every 6 hours 2
- Duration: 14-21 days 2
Prophylaxis:
- 150 mg/m²/day of TMP with 750 mg/m²/day of SMX, divided into 2 doses 3
- Administer 3 consecutive days per week (preferred schedule) 3
- Alternative: daily administration or 3 times weekly on alternate days 3
- Maximum daily dose: 320 mg TMP and 1600 mg SMX 2
Age-Specific Considerations
Infants and Young Children (<2 years)
- Not recommended for infants less than 2 months of age 2
- For children 2 months to <6 years requiring high-dose therapy: 15/75 mg/kg/day of TMP/SMX divided every 12 hours matches adult high-dose exposure 4
School-Age Children (6-21 years)
- For high-dose therapy: 12/60 mg/kg/day of TMP/SMX divided every 12 hours matches adult high-dose exposure 4
Formulation and Administration
- Use liquid formulation for children weighing <16 kg to ensure accurate dosing 1
- The standard 8/40 mg/kg/day dosing achieves therapeutic targets for bacteria with MIC ≤0.5 mg/L in >90% of children 1
Renal Impairment Dosing
- Creatinine clearance >30 mL/min: Use standard dosing 2
- Creatinine clearance 15-30 mL/min: Reduce to 50% of usual regimen 2
- Creatinine clearance <15 mL/min: Use not recommended 2
- Alternative approach: Increase dosing interval (hours) to 12 times the serum creatinine level (mg/dL), maximum 48 hours 5
Monitoring Requirements
- Obtain complete blood count with differential and platelet count at treatment initiation 1
- Repeat CBC monthly during prolonged therapy to assess for hematologic toxicity, particularly thrombocytopenia 1, 5
- Monitor serum TMP levels in severe renal failure 5
Critical Safety Warnings
- Use with extreme caution in G6PD deficiency due to hemolytic anemia risk 1
- Increases methotrexate toxicity, warfarin anticoagulant effect, and hypoglycemia risk with oral hypoglycemics 1
- Higher serum TMP levels and longer treatment duration correlate with thrombocytopenia risk 5
- Common adverse effects include rash, gastrointestinal disturbances, and hematologic abnormalities 3
Dosing Pitfalls to Avoid
- Do not use weight-based dosing alone in very young children—body surface area dosing (mg/m²) is more accurate for PCP prophylaxis 3, 2
- The standard 8/40 mg/kg/day dosing is inadequate for bacteria with MIC >0.5 mg/L; increase to 12/60 mg/kg/day for MIC up to 1 mg/L 4
- Avoid underdosing in serious infections—the FDA label's "40 mg/kg/day" represents the lower end; use 60 mg/kg/day of SMX for severe infections 1, 2