Trimethoprim-Sulfamethoxazole Dosing for MRSA Wound Infections
For MRSA wound infections, the recommended oral dosage of trimethoprim-sulfamethoxazole (TMP-SMX) is 160-800 mg (one double-strength tablet) twice daily. 1
Dosing Considerations
- Standard adult dosing: One double-strength tablet (160 mg TMP/800 mg SMX) twice daily
- Duration: 7-14 days for uncomplicated skin and soft tissue infections
- Higher dosing (two double-strength tablets twice daily) has not shown improved clinical outcomes compared to standard dosing 2
Clinical Evidence
The 2014 Infectious Diseases Society of America (IDSA) guidelines for skin and soft tissue infections recommend TMP-SMX as an effective oral option for MRSA wound infections 1. TMP-SMX demonstrates good activity against aerobic bacteria including MRSA, though it has poor activity against anaerobes 1.
Recent clinical trials have confirmed TMP-SMX's efficacy:
- A randomized trial showed TMP-SMX was effective for drained cutaneous abscesses in settings where MRSA is prevalent 3
- When compared with clindamycin for uncomplicated wound infections, TMP-SMX showed similar cure rates (91.9% vs 92.1%) 4
Treatment Algorithm
Confirm MRSA infection:
- Culture wound drainage when possible
- Consider empiric MRSA coverage in high-prevalence areas
Assess infection severity:
- For uncomplicated infections: Oral TMP-SMX 160-800 mg twice daily
- For severe infections: Consider initial IV therapy with vancomycin (30 mg/kg/day in 2 divided doses) 5
Adjunctive therapy:
- Incision and drainage is critical for abscesses
- Consider adding coverage for anaerobes if mixed infection suspected
Duration of therapy:
- 7-14 days for uncomplicated infections
- Extend treatment for complicated infections based on clinical response
Important Considerations and Pitfalls
- TMP-SMX lacks activity against streptococci and anaerobes; consider combination therapy if these pathogens are suspected 1
- For severe MRSA infections with bacteremia, TMP-SMX may be less effective than vancomycin 6
- Monitor for adverse effects including gastrointestinal symptoms, rash, and rare but serious reactions like Stevens-Johnson syndrome
- Consider alternative agents (minocycline, doxycycline, clindamycin) in cases of TMP-SMX allergy or treatment failure 7
- Avoid TMP-SMX in late pregnancy and in patients with significant renal impairment
By following these evidence-based recommendations, clinicians can effectively treat MRSA wound infections while minimizing complications and treatment failures.