Is Septra (trimethoprim/sulfamethoxazole) effective for treating potential Methicillin-resistant Staphylococcus aureus (MRSA) + impetigo?

Septra for MRSA and Impetigo Treatment

Yes, Septra (trimethoprim-sulfamethoxazole/TMP-SMX) is effective for treating both potential MRSA and impetigo, making it an appropriate single-agent choice for this clinical scenario. 1

Evidence for MRSA Coverage

TMP-SMX is explicitly recommended by the Infectious Diseases Society of America (IDSA) as a first-line oral antibiotic option for empirical coverage of community-acquired MRSA in outpatients with skin and soft tissue infections. 1

• For purulent cellulitis (cellulitis with purulent drainage or exudate), empirical therapy for CA-MRSA is recommended pending culture results, and TMP-SMX is listed as an A-II level recommendation 1
• TMP-SMX has become increasingly prescribed in emergency departments for skin infections, reaching 51% of MRSA-active regimens by 2005, reflecting its clinical acceptance 2
• The drug provides reliable coverage against most community-acquired MRSA strains 3, 4

Evidence for Impetigo Coverage

Impetigo is caused by β-hemolytic Streptococcus species and/or S. aureus, with rising involvement of CA-MRSA as an etiological agent. 1

• Since impetigo can be caused by both streptococci and S. aureus (including MRSA), antibiotic selection must address both pathogens 1
• TMP-SMX provides excellent coverage for S. aureus including MRSA strains 1, 3

Critical Limitation: Streptococcal Coverage Gap

The major caveat is that TMP-SMX alone does NOT reliably cover β-hemolytic streptococci, which are common impetigo pathogens. 1

• When coverage for both β-hemolytic streptococci and CA-MRSA is desired, IDSA recommends either:
  • Clindamycin alone (covers both organisms) 1
  • TMP-SMX or a tetracycline in combination with a β-lactam (e.g., amoxicillin) 1
  • Linezolid alone (covers both organisms) 1

Clinical Decision Algorithm

For impetigo with suspected MRSA involvement:

• If the infection appears purely purulent with no concern for streptococcal involvement: TMP-SMX alone (1-2 double-strength tablets twice daily) is appropriate 1, 3
• If classic impetigo features are present (honey-crusted lesions suggesting streptococcal etiology) OR if you cannot definitively exclude streptococcal involvement: Add amoxicillin to TMP-SMX, or switch to clindamycin monotherapy 1
• For children with minor impetigo: Topical mupirocin 2% ointment can be used as an alternative 1

Treatment Duration and Monitoring

• Treat for 5-10 days based on clinical response 1
• Reevaluate within 24-48 hours to verify clinical response, as treatment failure rates of 21% have been reported with oral agents for MRSA 5, 6
• Obtain cultures from purulent lesions if the patient has severe infection, systemic illness, or fails to respond to initial treatment 1

Pediatric Considerations

• TMP-SMX can be used in children, unlike tetracyclines which are contraindicated under age 8 1, 6
• Topical mupirocin remains an excellent option for minor pediatric impetigo 1

Comparative Effectiveness

• A randomized trial showed TMP-SMX and clindamycin had similar cure rates (91.9% vs 92.1%) for uncomplicated wound infections, though clindamycin had lower recurrence rates (7.1% vs 2.0%) 7
• Some evidence suggests minocycline may be more reliably effective than TMP-SMX when doxycycline or TMP-SMX fails 8

Bottom line: TMP-SMX covers MRSA excellently but misses streptococci. For impetigo, either add a β-lactam to TMP-SMX or use clindamycin monotherapy to ensure complete coverage of both likely pathogens. 1