Clindamycin or trimethoprim-sulfamethoxazole improves cure rate after incision and drainage of S. aureus or MRSA-infected uncomplicated skin abscess ≤ 5 cm

EBM Focus - Volume 12, Issue 31

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Reference: N Engl J Med 2017 Jun 29;376(26):2545 (level 1 [likely reliable] evidence)

  • Incision and drainage is the primary therapy recommended for uncomplicated skin abscesses.
  • The efficacy of adjunct antibiotic therapy was evaluated in 786 patients (35.8% < 18 years old) with a single uncomplicated skin abscess ≤ 5 cm in diameter that was incised and drained. The patients were randomized to clindamycin 300 mg orally 3 times daily vs. trimethoprim-sulfamethoxazole (TMP-SMX) 160 mg/800 mg orally twice daily vs. placebo for 10 days.
  • The rate of clinical cure 7 to 10 days after the end of treatment was achieved in 83.1% with clindamycin (p < 0.001 vs. placebo, NNT 7), 81.7% with TMX-SMX (p < 0.001 vs. placebo, NNT 8), and 68.9% with placebo. The high cure rate attained without antibiotics suggests that their use may be reserved for patients who do not improve after performing incision and drainage.

The Infectious Disease Society of America (IDSA) recommends incision and drainage as the primary therapy for uncomplicated skin abscesses with the addition of systemic antibiotics active against Staphylococcus aureus in patients with signs of systemic inflammatory response syndrome (Clin Infect Dis. 2014 Jul 15;59(2):e10-52). Clindamycin and TMP-SMX are active against both methicillin-sensitive and community-associated methicillin-resistant S. aureus (MRSA) strains. To evaluate the efficacy of adjunct antibiotic therapy for uncomplicated abscesses, 786 patients (35.8% < 18 years old) with a single uncomplicated skin abscess ≤ 5 cm that was incised and drained were randomized to clindamycin 300 mg orally 3 times daily vs. trimethoprim-sulfamethoxazole (TMP-SMX) 160 mg/800 mg orally twice daily vs. placebo for 10 days. Failure of clinical cure was defined as any of the following: lack of resolution of signs or symptoms of infection, discontinuation of medication within 48 hours due to adverse effects, recurrence of infection or new infection, unplanned surgical treatment, or hospitalization related to infection.

Staphylococcus aureus was isolated in 67% and MRSA in 49.4% of patients. Clinical cure 7 to 10 days after the end of treatment was achieved in 83.1% with clindamycin (p < 0.001 vs. placebo, NNT 7), 81.7% with TMX-SMX (p < 0.001 vs. placebo, NNT 8), and 68.9% with placebo. Consistent results for clinical cure rates were observed in subgroup analyses of patients < 18 years old, with cultures positive for S. aureus, or with cultures positive for methicillin-resistant S. aureus. In patients with a clinical cure 7 to 10 days after the end of treatment, a new infection or recurrent infection at 1 month occurred in 6.8% with clindamycin (p = 0.06 vs. placebo), 13.5% with TMP-SMX (not significant vs. placebo), and 12.4% with placebo. Adverse events occurred in 21.9% with clindamycin, 11.1% with TMP-SMX, and 12.5% with placebo (statistical comparisons not reported) with the most common events being diarrhea and nausea. One patient taking TMP-SMX had a hypersensitivity reaction with fever, rash, thrombocytopenia, and hepatitis.

This trial indicates that the addition of either clindamycin or TMP-SMX to incision and drainage of small uncomplicated abscesses improves clinical cure rates in outpatients. These results are consistent with another high quality trial involving 1,247 adults and adolescents with an abscess ≥ 2 cm in diameter and with a similar rate of MRSA-positive cultures randomized to adjunctive TMP-SMX for 7 days vs. placebo (N Engl J Med 2016 Mar 3;374(9):823). However, the clinical cure rate in the placebo group in both trials was about 70% suggesting that the majority of patients with uncomplicated skin abscess do not require antibiotic therapy. For a discussion of the trial published in 2016, please see EBM Focus Volume 11 Issue 11. Inappropriate prescription of antibiotics during ambulatory care visits in the United States is estimated to occur in 30% of patients of all ages (JAMA 2016 May 3;315(17):1864), unnecessarily contributing to the emergence of bacterial resistance. The consequences of bacterial resistance to antibiotics are highlighted by estimates indicating that 2,049,442 illnesses and 23,488 deaths occur annually in the United States due to antibiotic resistant microorganisms (Centers for Disease Control and Prevention (CDC) Antibiotic Resistance Threats in the United States 2013). Given that the emergence of antibiotic resistant bacteria poses substantial risks to society and that almost 70% of patients with an uncomplicated abscess achieve a cure with incision and drainage alone, clinicians may want to consider waiting to see which patients fail to respond to incision and drainage before starting antibiotics. This approach would also decrease the risk of antibiotic-associated adverse events.

For more information see the Skin abscesses, furuncles, and carbuncles and Approach to rational antibiotic use in the outpatient setting topics in DynaMed Plus. DynaMed users click here.


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