We can't draw firm conclusions from this paper, since it was not designed or powered to detect differences in subgroups with skin abscesses. But it was notable that patients who received TMP/SMX did better than those who received placebo across all subgroups, including those with larger abscesses; especially those with fever, history of MRSA, or MRSA positive culture.
Why does this matter?
The CDC and IDSA guidelines state that incision and drainage alone is generally sufficient treatment. However, two recent RCTs have challenged that paradigm. First, Talan et al found TMP/SMX in addition to routine I&D was superior to placebo. In a more recent RCT, TMP/SMX was superior to placebo specifically for small abscesses < 5 cm. Here, Talan et al present a planned subgroup analysis of abscess/erythema size, fever, comorbidities, MRSA positive culture, and history of prior MRSA.
Antibiotics good for abscesses
This was a planned subanalysis of a prior RCT with 1057 patients, mostly adults. The original study found TMP/SMX was beneficial in patients who underwent I&D and received the antibiotic vs placebo. This study was exploratory and not powered to detect these subgroup analysis differences but was suggestive nonetheless. They found that the clinical cure rate (no additional antibiotics) in 7-14 days and composite cure rate (no antibiotics or repeat I&D) was better in the patients who received TMP/SMX across all subgroups. Improvements in composite cure rate persisted out to 56 days. Patients with prior history of MRSA, fever, or positive MRSA cultures had even greater benefit. Of course, with multiple comparisons, some of the improvement in the subgroups could have been due to chance. This study was hypothesis generating and not definitive but suggested that prescribing TMP/SMX for patients with a cutaneous abscess of any size or subgroup was beneficial.
Subgroup Analysis of Antibiotic Treatment for Skin Abscesses. Ann Emerg Med. 2017 Oct 4. pii: S0196-0644(17)31383-5. doi: 10.1016/j.annemergmed.2017.07.483. [Epub ahead of print]
Peer reviewed by Thomas Davis, MD.