Is Bactrim (trimethoprim/sulfamethoxazole) a suitable choice for treating cellulitis when there's a concern for Methicillin-resistant Staphylococcus aureus (MRSA) infection?

Bactrim (TMP-SMX) for Cellulitis with Concern for MRSA

Bactrim (trimethoprim-sulfamethoxazole) is an appropriate first-line treatment choice for cellulitis when there is concern for MRSA infection, especially in cases of purulent cellulitis. 1

Treatment Algorithm Based on Cellulitis Type

Purulent Cellulitis (with drainage/exudate)

• Empirical therapy for community-acquired MRSA (CA-MRSA) is recommended pending culture results 1
• Recommended oral antibiotic options include:
  • Trimethoprim-sulfamethoxazole (TMP-SMX) (A-II evidence) 1
  • Clindamycin (A-II evidence) 1
  • Doxycycline or minocycline (A-II evidence) 1
  • Linezolid (A-II evidence, but more expensive) 1

Non-purulent Cellulitis (no drainage/exudate)

• Primary treatment should target beta-hemolytic streptococci with a beta-lactam antibiotic like cephalexin or amoxicillin 1
• MRSA coverage should be added if:
  • Patient fails to respond to beta-lactam therapy 1
  • Patient has systemic toxicity 1
  • There is evidence of MRSA infection elsewhere 1
  • Patient has history of MRSA colonization 1
  • Patient has history of injection drug use 1

Evidence Supporting Bactrim for MRSA Cellulitis

• The Infectious Diseases Society of America (IDSA) guidelines specifically recommend TMP-SMX as a first-line agent for purulent cellulitis where CA-MRSA is suspected 1
• In areas with high MRSA prevalence, TMP-SMX has shown significantly higher treatment success rates (91%) compared to cephalexin (74%) for outpatient cellulitis treatment 2
• Standard dosing of TMP-SMX (160mg/800mg twice daily) appears to be as effective as higher dosing (320mg/1600mg twice daily) for MRSA skin infections 3

Important Clinical Considerations

• When coverage for both beta-hemolytic streptococci and CA-MRSA is desired, options include:

  • Clindamycin alone (A-II) 1
  • TMP-SMX or tetracycline in combination with a beta-lactam like amoxicillin (A-II) 1
  • Linezolid alone (A-II) 1

• Duration of therapy should be 5-10 days, individualized based on clinical response 1

• Cultures should be obtained from:

  • Abscesses and purulent drainage 1
  • Patients with severe local infection or systemic illness 1
  • Patients who have not responded to initial treatment 1

Potential Pitfalls and Caveats

• TMP-SMX has excellent activity against MRSA but may have limited activity against beta-hemolytic streptococci 1

  • This is why combination with a beta-lactam may be considered when streptococcal infection is also suspected 1

• TMP-SMX is not recommended for:

  • Women in the third trimester of pregnancy 1
  • Children under 2 months of age 1

• A recent randomized clinical trial (2017) found that adding TMP-SMX to cephalexin did not significantly improve clinical cure rates in the per-protocol analysis of uncomplicated cellulitis, though the modified intention-to-treat analysis suggested a possible benefit 4

• For non-purulent cellulitis without risk factors for MRSA, a beta-lactam antibiotic alone remains the first-line recommendation 1

In this specific case, where there is concern for possible MRSA infection, your preceptor's choice of Bactrim is well-supported by current guidelines and evidence, particularly if the cellulitis has purulent features or if there are risk factors for MRSA infection 1, 2.