Bactrim Dosage for MRSA Cellulitis in a 9-Year-Old Weighing 46 kg
For a 9-year-old child weighing 46 kg with MRSA cellulitis, the recommended dosage of trimethoprim-sulfamethoxazole (TMP-SMX) is 8-12 mg/kg/day of the trimethoprim component divided into two doses every 12 hours for 5-10 days. 1, 2
Specific Dosing Calculation
Based on the patient's weight of 46 kg:
- TMP component: 8-12 mg/kg/day = 368-552 mg/day
- This translates to 184-276 mg of TMP per dose, given twice daily
In practical terms:
- For this 46 kg child, 2 regular-strength tablets (80 mg TMP/400 mg SMX per tablet) or 1 double-strength tablet (160 mg TMP/800 mg SMX) twice daily would be appropriate 2
- According to the FDA drug label weight-based dosing table, a child weighing 40-88 kg should receive 2 regular-strength tablets or 1 double-strength tablet every 12 hours 2
Treatment Considerations
Duration of Therapy
- Treatment should continue for 5-10 days, depending on clinical response 1, 3
- If the infection has not improved within 5 days, consider extending treatment or reevaluating the diagnosis 3
Monitoring
- Monitor for clinical improvement within 48-72 hours
- Watch for adverse effects including:
- Gastrointestinal disturbances
- Skin rashes
- Hematologic abnormalities
- Hyperkalemia
Weight-Based Dosing Importance
- Adequate weight-based dosing (≥5 mg TMP/kg/day) is essential to prevent clinical failure 4
- A study showed that inadequate dosing was independently associated with clinical failure in cellulitis (OR = 2.01, p = 0.032) 4
Alternative Options
If TMP-SMX cannot be used due to allergies or other contraindications:
- Clindamycin: 10-13 mg/kg/dose orally every 6-8 hours, not exceeding 40 mg/kg/day 1
- Linezolid: 10 mg/kg/dose orally every 8 hours, not to exceed 600 mg/dose 1
- Doxycycline: For children ≥8 years old, 2 mg/kg/dose orally every 12 hours (not exceeding 100 mg per dose) 1
Important Caveats
- TMP-SMX is not recommended for children under 2 months of age 2
- TMP-SMX has excellent coverage for MRSA but may have limited activity against β-hemolytic streptococci 1
- For severe infections with systemic symptoms, consider intravenous therapy with vancomycin (15 mg/kg/dose IV every 6 hours) 1
- Incision and drainage should be performed if there is a purulent collection 1
By following these dosing guidelines and monitoring parameters, you can effectively treat MRSA cellulitis in this pediatric patient while minimizing the risk of treatment failure and adverse effects.