Bactrim Suspension Dosing for a 69 lb Child
For a 69 lb (31 kg) child, the recommended dose of Bactrim suspension is based on 40 mg/kg/day of sulfamethoxazole and 8 mg/kg/day of trimethoprim, divided into two doses every 12 hours, which equals approximately 1,240 mg sulfamethoxazole and 248 mg trimethoprim per day (620 mg/124 mg per dose twice daily). 1
Standard Treatment Dosing
For most common indications (urinary tract infections, acute otitis media, shigellosis):
The FDA-approved dosing is 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, given in two divided doses every 12 hours. 1
For a 69 lb (31 kg) child, this translates to:
- Total daily dose: 1,240 mg sulfamethoxazole + 248 mg trimethoprim
- Per dose (every 12 hours): 620 mg sulfamethoxazole + 124 mg trimethoprim 1
Using standard Bactrim suspension (200 mg sulfamethoxazole/40 mg trimethoprim per 5 mL), this equals approximately 15.5 mL twice daily. 1
Practical Tablet-Based Dosing Alternative
The FDA label provides a simplified weight-based tablet dosing: for children weighing 66-88 lb, give 1.5 tablets (or 2 single-strength tablets) every 12 hours. 1
- This corresponds to 600 mg sulfamethoxazole/120 mg trimethoprim per dose, which is clinically equivalent to the calculated dose above 1
Duration of Treatment
- For urinary tract infections and acute otitis media: 10 days 1
- For shigellosis: 5 days 1
- For acute exacerbations of chronic bronchitis (if applicable): 14 days 1
Special Considerations
Pneumocystis Prophylaxis Dosing (If Indicated)
For prophylaxis in immunocompromised children, the CDC recommends 8 mg/kg/day of trimethoprim component divided into two doses, which can be given three consecutive days per week as an alternative to daily administration. 2
Renal Function
When creatinine clearance is less than 30 mL/min, dosage adjustment is required; use half the usual regimen for creatinine clearance 15-30 mL/min, and avoid use below 15 mL/min. 1
Monitoring
For prophylactic use, the CDC recommends complete blood counts with differential and platelet count at initiation and monthly thereafter to assess for hematologic toxicity. 2
Common Pitfalls to Avoid
- Do not use Bactrim in children less than 2 months of age—it is contraindicated. 1
- Ensure adequate hydration to prevent crystalluria, particularly with higher doses. 3
- Be aware that peak drug levels are higher and more reliable with IV administration compared to oral dosing, though oral absorption is generally adequate for most infections. 4
- Common adverse effects include rash, gastrointestinal disturbances, and hematologic abnormalities; if life-threatening toxicity occurs, permanently discontinue the drug. 2