Bactrim Dosing for 96lb 8-Year-Old
For an 8-year-old child weighing 96 pounds (43.6 kg), the appropriate dose of Bactrim (trimethoprim-sulfamethoxazole) 200-40mg/5mL suspension is 8-12 mg/kg/day based on the trimethoprim component, divided into 2 doses every 12 hours, which translates to approximately 17.5-26 mL (350-520 mg trimethoprim component) per day, or 8.75-13 mL twice daily. 1
Weight-Based Calculation
- Patient weight: 96 pounds = 43.6 kg
- Standard pediatric dosing: 8-12 mg/kg/day of trimethoprim component in 2 divided doses 1
- Trimethoprim daily dose range: 349-523 mg/day (43.6 kg × 8-12 mg/kg)
- Suspension concentration: 40 mg trimethoprim per 5 mL
- Volume per dose: 8.75-13 mL twice daily (every 12 hours)
Dosing by Indication
The specific dose within this range depends on the infection being treated:
For Skin and Soft Tissue Infections (SSTI)
- Dose: 8-12 mg/kg/day trimethoprim component in 2 divided doses orally 1
- Volume: 8.75-13 mL twice daily
- Duration: Typically 7-10 days depending on clinical response 1
For Urinary Tract Infections
- Dose: 8 mg/kg trimethoprim component per 24 hours in 2 divided doses 2
- Volume: Approximately 8.75 mL twice daily
- Duration: 10-14 days 2
For Acute Otitis Media
- Dose: 8 mg/kg trimethoprim component per 24 hours in 2 divided doses 2
- Volume: Approximately 8.75 mL twice daily
- Duration: 10 days 2
Important Clinical Considerations
Age appropriateness: This child is 8 years old, which is well above the minimum age of 2 months for trimethoprim-sulfamethoxazole use. 1, 2
Contraindications to verify:
- Not contraindicated in children ≥2 months of age 2
- Avoid in documented megaloblastic anemia due to folate deficiency 1
- Avoid in known hypersensitivity to trimethoprim or sulfonamides 1
Monitoring for adverse effects:
- Stevens-Johnson syndrome and toxic epidermal necrolysis are rare but serious risks 1
- Thrombocytopenia may occur, particularly with higher serum levels and longer treatment duration 3
- Gastrointestinal upset and skin rashes can occur but are generally less frequent than with other antibiotics 4
Practical Dosing Recommendation
For most common pediatric infections in this 96-pound child, prescribe 10 mL of Bactrim suspension (200-40mg/5mL) twice daily (every 12 hours), which provides 10 mg/kg/day of trimethoprim—the middle of the recommended range. 1, 2
This provides:
- 80 mg trimethoprim per dose (160 mg/day total)
- 400 mg sulfamethoxazole per dose (800 mg/day total)
- Trimethoprim dose: 10 mg/kg/day (436 mg ÷ 43.6 kg)
Renal function: Ensure normal renal function; if creatinine clearance is <30 mL/min, reduce dose to half the usual regimen. 2