Annual emergency department visits for skin and soft tissue infections (SSTI) are on the rise nationwide, and an increased incidence of abscesses is the likely culprit. MRSA is quickly emerging as the most common cause of purulent SSTIs, and Trimethoprim-Sulfamethoxazole (TMP-SMX) remains a cost-effective first line enteral antimicrobial to treat it. The primary treatment for a cutaneous abscess is incision and drainage (I&D), and previous investigations have shown no benefit to adjunctive antibiotic therapy. Moreover, many of the respected academic societies also recommend I&D alone for the treatment of an uncomplicated abscess.

Clinical Question

Is clinical cure of cutaneous abscesses that are I&D’d in the ED improved by a 7 day course of TMP-SMX versus placebo?


Patients aged > 12 with a superficial abscess




I+D + placebo


Primary: Clinical cure at the test-of-cure visit
Secondary: Composite cure (resolution of all symptoms and signs of infection), subsequent surgical drainage procedures, skin infections at new sites, infections in household members, changes in erythema size, presence of swelling or induration or tenderness, invasive infections, hospitalizations.


Multicenter, double-blinded, randomized trial conducted with intention-to-treat analysis


Indwelling device; suspected osteomyelitis or septic arthritis; diabetic foot, decubitus, or ischemic ulcer; mammalian bite; wound with organic foreign body; infection of another organ system/site; perirectal, perineal or paronychial location; intravenous drug use within previous month and fever; underlying skin condition; long-term care residence; incarceration; immunodeficiency (e.g., absolute neutrophil count <500/mm3 , immunosuppressive drugs, active chemotherapy, or known AIDS assessed by subject history); creatinine clearance <50 mL/min; cardiac condition with risk of endocarditis; allergy or intolerance to trimethoprim-sulfamethoxazole; taking warfarin, phenytoin, or methotrexate; known G-6-PD or folic acid deficiency; pregnant or lactating; trimethoprim-sulfamethoxazole treatment within 24 hours; concurrent treatment with topical or systemic antibiotic; or enrolled in the study within 12 weeks.

Primary Results

  • 1265 patients included in the study over five different sites.
  • MRSA found in 45.3% of participants.

Critical Results

  • Modified intention to treat group
    • 80.5% vs. 73.6% cure rate (TMP-SMX vs. placebo)
    • Absolute difference 6.9% (CI: 2.1 – 11.7 p = 0.005)
    • NNT = 14
  • Per protocol group
    • 92.9% vs. 85.7% cure rate (TMP-SMX vs. placebo)
    • Absolute difference 7.2% (CI: 3.2 – 11.2 p < 0.001)

Secondary Results:

  • Recurrent surgical drainage: 3.4% in TMP-SMX vs 8.6% in placebo
  • Skin infections at new sites: 3.1%in TMP-SMX vs 10.3% in placebo
  • Infections in household members: 1.7%in TMP-SMX vs 4.1% in placebo
  • GI side effects: 42.7%in TMP-SMX vs 36.1% in placebo


  • Large, multicenter, RCT with excellent methodology
  • Appropriate randomization techniques
  • Study asked a clear clinical question
  • Powered appropriately for the primary outcome
  • Applicable to many ED patients


  • Potential for enrollment bias as providers may not have included higher risk patients not in the study’s exclusion criteria
  • Many of the patients enrolled would have met standard practice guideline criteria to receive adjunctive antimicrobial therapy, as cellulitis and diabetes were not exclusion criteria
  • The “clinical failure” criteria used by the authors was not externally validated criteria
  • I+D skills differ amongst providers, thus cure rates in the placebo group may actually be higher if some of the abscesses were not fully drained
  • Study not powered high enough to assess the rate of rare adverse side effects of TMP-SMX

Author's Conclusions

“In settings in which MRSA was prevalent, trimethoprim-sulfamethoxazole treatment resulted in a higher cure rate among patients with a drained cutaneous abscess than placebo.”

Our Conclusions

TMP-SMX may be helpful in patients with an abscess in which you anticipate failure of I+D alone, and it may also help prevent infections at new sites and decrease the rate of recurrent I+D.

Potential Impact To Current Practice

Empiric TMP-SMX for all uncomplicated abscess may help increase clinical cure rates, but it also may result in more adverse side effects and has the potential to breed resistance to TMP-SMX.

Bottom Line

ED providers should not take the results of this study to mean that all patients with abscesses that are I+D’d in the ED should be discharged on TMP-SMX. The majority of patients with abscesses will improve with I+D alone. The presence of significant overlying cellulitis continues to warrant adjunctive therapy with antibiotics.

Read More

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