Adjunctive Trimethoprim-Sulfamethoxazole Improves Cure Rate of Uncomplicated Skin Abscesses

EBM Focus - Volume 11, Issue 11

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Reference - N Engl J Med 2016 Mar 3;374(9):823 (level 1 [likely reliable] evidence)

Incision and drainage is the primary therapy recommended for uncomplicated skin abscesses (Clin Infect Dis 2014 Jul 15;59(2):e10). In most cases, systemic antibiotics are not necessary and are recommended against (Clin Infect Dis 2014 Jul 15;59(2):e10, Choosing Wisely Canada 2015 Jun 2). However, if adjunctive systemic antibiotics are prescribed, agents active against methicillin-resistant Staphylococcus aureus (MRSA) are commonly used due to high rates of MRSA in these infections. One such agent is trimethoprim-sulfamethoxazole. Previous trials evaluating its benefit in patients with uncomplicated skin abscess did not show a significant difference in outcomes, but all were underpowered. A recent trial randomized 1,265 patients (median age 35 years) with skin abscess ≥ 2 cm diameter having incision and drainage to trimethoprim-sulfamethoxazole 320 mg/1,600 mg vs. placebo twice daily for 7 days. All included patients were ≥ 12 years old and had the lesion for < 1 week.

Patients were assessed for a clinical cure, defined as a therapeutic response plus the absence of fever assessed throughout treatment and at the test-of-cure visit at day 14-21. All patients who received ≥ 1 dose of trial medication (98.6%) were included in the modified intention-to-treat analysis and 83.6% of patients were included in the per-protocol analysis. MRSA was isolated in 45% of patients. Comparing trimethoprim-sulfamethoxazole vs. placebo, a clinical cure was attained in 80.5% vs. 73.6% in the modified intention-to-treat analysis (p = 0.005, NNT 15) and 92.9% vs. 85.7% in the per-protocol population (p < 0.001, NNT 14). In the per-protocol population, trimethoprim-sulfamethoxazole was also associated with a reduced need for additional surgical drainage and reduced new skin infection at a different site within 21 days. There were no significant differences in hospitalization rates, recurrent skin infections at the original site, presence of swelling or tenderness, or adverse events.

While this trial suggests that some patients may benefit from adjunctive trimethoprim-sulfamethoxazole therapy, the vast majority of patients were able to clear the infection with incision and drainage alone. The 7% difference in cure rate between groups should not be interpreted as an indication for antibiotics in all patients with uncomplicated abscesses. With the growing rates of antibiotic resistant organisms in skin abscesses and other infections, potentially unnecessary antibiotic use needs to be carefully weighed against the risks to both the patient and the community. Further investigation is needed to determine which patients may derive the most benefit from adjunctive treatment or other management strategies. In the meantime, consistent with the Infectious Disease Society of America guidelines, adjunctive trimethoprim-sulfamethoxazole may be considered for select patients with uncomplicated skin abscesses, such as those with multiple lesions, those at the extremes of age, and those with recurrent abscesses or a failure to respond to incision and drainage.

For more information, see the Skin abscesses, furuncles, and carbuncles topics in DynaMed Plus. DynaMed users click here.