Recommended Dosage of Trimethoprim-Sulfamethoxazole for MRSA Skin Infections
For treating MRSA skin infections, trimethoprim-sulfamethoxazole (TMP-SMX) should be administered at a dosage of 1-2 double-strength tablets (each containing 160mg trimethoprim and 800mg sulfamethoxazole) twice daily for adults. 1
Adult Dosing
- 1-2 double-strength tablets (160mg/800mg) twice daily orally
- Duration of therapy is typically 7 days, depending on clinical response 1
- For more severe infections, the higher dose (2 double-strength tablets twice daily) is preferred
Pediatric Dosing
- 8-12 mg/kg/day (based on the trimethoprim component) in either:
- 4 divided doses if given intravenously
- 2 divided doses if given orally 1
- Not appropriate for neonates (refer to American Academy of Pediatrics guidelines for neonatal doses)
Clinical Efficacy
TMP-SMX is characterized as bactericidal against MRSA skin infections, though earlier guidelines noted limited published efficacy data 1. However, more recent research has demonstrated its effectiveness:
- A randomized trial showed TMP-SMX resulted in higher cure rates (80.5% vs 73.6% with placebo) for drained cutaneous abscesses in settings where MRSA was prevalent 2
- For MRSA skin abscesses, a 10-day course of TMP-SMX after surgical drainage is superior to a 3-day course, with lower treatment failure and recurrence rates 3
Treatment Algorithm for MRSA Skin Infections
For minor, uncomplicated MRSA skin infections:
- Incision and drainage is the primary treatment
- Add TMP-SMX (1 double-strength tablet twice daily) for 7 days
For moderate MRSA skin infections:
- Incision and drainage plus
- TMP-SMX (2 double-strength tablets twice daily) for 7-10 days
For severe or complicated MRSA skin infections:
- Consider initial intravenous therapy with vancomycin, linezolid, or daptomycin
- Switch to oral TMP-SMX when clinically improving
Important Considerations
Surgical drainage is critical - patients who receive both incision and drainage plus antibiotics have significantly lower failure rates (25%) compared to those receiving incision and drainage alone (60%) 4
Alternative oral options if TMP-SMX cannot be used:
- Clindamycin: 300-450mg four times daily (if local resistance rates are low)
- Doxycycline or minocycline: 100mg twice daily (not for children <8 years)
- Linezolid: 600mg twice daily (expensive option) 1
Monitoring: Watch for adverse effects of TMP-SMX, including:
- Gastrointestinal side effects (most common but usually mild) 2
- Skin rashes
- Rare but serious reactions: Stevens-Johnson syndrome, bone marrow suppression
Treatment failure: If inadequate response to TMP-SMX, consider minocycline as an alternative, which may be effective when TMP-SMX fails 5
TMP-SMX remains a first-line oral therapy for MRSA skin infections due to its efficacy, relatively low cost, and good tissue penetration. The combination of proper surgical drainage and appropriate antibiotic therapy offers the best outcomes for patients with MRSA skin infections.