Cotrimoxazole (Trimethoprim-Sulfamethoxazole) Dosing in Pediatrics
For treatment of infections in children >2 months of age, the standard dose is 8-12 mg/kg/day of the trimethoprim component, divided into 2 doses every 12 hours. 1, 2
Treatment Dosing by Clinical Indication
Mild to Moderate Infections
- 8-12 mg/kg/day of trimethoprim component divided into 2 doses every 12 hours 3, 1, 2
- This translates to 40-60 mg/kg/day of the sulfamethoxazole component 3
- Typical treatment duration is 7-10 days depending on clinical response 2
Severe Infections (Pneumocystis jiroveci pneumonia)
- 15-20 mg/kg/day of trimethoprim component administered intravenously in 3-4 divided doses 3
- This equals 75-100 mg/kg/day of the sulfamethoxazole component 3
- Each IV dose should be infused over 1 hour 3
- Treatment duration is 21 days for PCP 3
- After acute pneumonitis resolves, can switch to oral therapy at the same dose if no malabsorption or diarrhea present 3
Complicated Infections Requiring IV Therapy
- 8-12 mg/kg/day of trimethoprim divided into 4 doses IV 4
- For CNS infections or severe bacteremia: 5 mg/kg/dose IV every 8-12 hours 4
Prophylaxis Dosing
Standard Prophylactic Regimen
- 8 mg/kg/day of trimethoprim component divided into 2 doses 1
- Alternative: 150 mg/m²/day of trimethoprim with 750 mg/m²/day of sulfamethoxazole, divided into 2 doses 1
- Can be given three consecutive days per week instead of daily 1
Critical Age and Safety Considerations
Age Restrictions
- Contraindicated in infants <2 months of age due to kernicterus risk 3
- Should not be given to pregnant women in third trimester or nursing mothers 3, 4
Monitoring Requirements
- Perform complete blood counts with differential and platelet count at initiation and monthly thereafter to assess for hematologic toxicity 1
- Watch for rash (including Stevens-Johnson syndrome), neutropenia, thrombocytopenia, hepatitis, and renal disorders 3, 2
- Maintain adequate fluid intake to prevent crystalluria and renal stones 3
Important Clinical Pitfalls
Cotrimoxazole has poor activity against beta-hemolytic streptococci, so it should not be used alone for non-purulent cellulitis where streptococci are likely pathogens 4. It also lacks anaerobic coverage and should not be used as monotherapy for mixed aerobic-anaerobic wound infections 4.
Adverse reactions occur in approximately 15% of HIV-infected children, which is lower than in adults 3. For mild rash, the drug can be temporarily discontinued and restarted when resolved, but if urticarial rash or Stevens-Johnson syndrome occurs, permanently discontinue 3, 1.