Pediatric Dosing of Bactrim (Trimethoprim-Sulfamethoxazole)
For pediatric patients, the recommended dose of Bactrim (trimethoprim-sulfamethoxazole) is 8-12 mg/kg/day of the trimethoprim component divided into two doses every 12 hours.
Standard Pediatric Dosing Guidelines
The FDA-approved dosing for Bactrim in pediatric patients is as follows:
- Children ≥2 months of age: 8 mg/kg/day of trimethoprim and 40 mg/kg/day of sulfamethoxazole divided into two doses every 12 hours 1
- Not recommended for infants <2 months of age due to risk of kernicterus 2, 1
Dosing by Indication
Urinary Tract Infections and Acute Otitis Media
- 8 mg/kg/day of trimethoprim component divided every 12 hours for 10 days 1
Shigellosis
Skin and Soft Tissue Infections (MRSA)
- 8-12 mg/kg/day (based on trimethoprim component) in 2 divided doses 2
Pertussis (Alternative Agent)
- For children >2 months: 8 mg/kg/day of trimethoprim component in 2 divided doses for 14 days 2
Pneumocystis jirovecii Pneumonia
- Treatment: 15-20 mg/kg/day of trimethoprim component divided every 6 hours for 14-21 days 1
- Prophylaxis: 150 mg/m²/day of trimethoprim component divided into two doses on 3 consecutive days per week 1
Weight-Based Dosing Chart
For standard dosing (8 mg/kg/day of trimethoprim component):
| Weight (kg) | Weight (lb) | Dose every 12 hours |
|---|---|---|
| 10 | 22 | 1 regular tablet (80 mg TMP/400 mg SMX) |
| 20 | 44 | 1 regular tablet |
| 30 | 66 | 1½ regular tablets |
| 40 | 88 | 2 regular tablets or 1 DS tablet |
Special Considerations
Renal Impairment
- For creatinine clearance 15-30 mL/min: reduce dose by 50%
- For creatinine clearance <15 mL/min: not recommended 1
Common Adverse Effects
- Gastrointestinal effects (nausea, vomiting, diarrhea)
- Hypersensitivity reactions (rash)
- Hematologic effects (monitor for thrombocytopenia with prolonged use) 4
Important Precautions
- Maintain adequate fluid intake to prevent crystalluria
- Monitor for potential drug interactions, particularly with methotrexate, oral anticoagulants, and antidiabetic agents 2
- TMP-SMX can be safely used concurrently with methotrexate in pediatric patients with inflammatory skin disease 2
Recent Evidence on Optimal Dosing
Recent pharmacokinetic studies suggest that higher doses may be needed for certain infections:
- For community-acquired MRSA infections: 8 mg/kg/day of trimethoprim component achieves target concentrations for bacteria with MIC ≤0.5 mg/L
- For less susceptible bacteria (MIC of 1 mg/L): 12-15 mg/kg/day may be required 5
For most common pediatric infections, the standard dose of 8 mg/kg/day of trimethoprim component divided every 12 hours remains appropriate and effective while minimizing adverse effects.