Bactrim Dosing for Skin Infection in a 28 kg Child
For a 28 kg child with a skin infection, the recommended dose of Bactrim (trimethoprim-sulfamethoxazole) is 8-12 mg/kg/day based on the trimethoprim component, given in 2 divided doses orally. 1
Dosage Calculation
Based on the child's weight of 28 kg:
Using the lower range (8 mg/kg/day of trimethoprim):
- 8 mg/kg/day × 28 kg = 224 mg/day of trimethoprim
- Divided into 2 doses = 112 mg trimethoprim per dose, twice daily
Using the upper range (12 mg/kg/day of trimethoprim):
- 12 mg/kg/day × 28 kg = 336 mg/day of trimethoprim
- Divided into 2 doses = 168 mg trimethoprim per dose, twice daily
Practical Administration
For a 28 kg child, the appropriate dosing would be:
- 1 regular-strength tablet (80 mg trimethoprim/400 mg sulfamethoxazole) twice daily
- This provides approximately 160 mg trimethoprim per day (5.7 mg/kg/day), which falls within the recommended range
This aligns with the FDA-approved dosing guideline that recommends the following for children 2 months of age or older 1:
- For a child weighing 20 kg: 1 tablet every 12 hours
- For a child weighing 30 kg: 1½ tablets every 12 hours
Since the child weighs 28 kg, the dosage would be closer to 1½ tablets every 12 hours, but 1 tablet twice daily is often used for simplicity and to avoid cutting tablets.
Treatment Duration
- Standard duration for skin infections is typically 7 days, depending on clinical response 2
- For MRSA skin infections, a 10-day course may be more effective in preventing treatment failure and recurrence 3
Important Considerations
Bactrim is contraindicated in children younger than 2 months of age 1
Monitor for adverse effects, including:
- Gastrointestinal disturbances
- Rash
- Bone marrow suppression (rare but serious)
- Hyperkalemia
Reassess the patient after 48-72 hours to evaluate treatment response
If the infection is suspected to be MRSA, ensure adequate duration of therapy (10 days) to prevent recurrence 3
Clinical Pearls
- Incision and drainage is the primary treatment for purulent skin infections; antibiotics are adjunctive therapy 2
- Bactrim has excellent activity against MRSA but less reliable activity against beta-hemolytic streptococci 2
- Concomitant use of Bactrim and methotrexate is not contraindicated according to pediatric dermatology guidelines 2
Remember to adjust dosing if renal function is impaired, though this is less common in pediatric patients without underlying conditions.