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Adding antibiotic improves treatment for skin abscesses
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Researchers at UCLA discovered that giving patients an antibiotic improved upon drainage-only treatment for uncomplicated skin abscesses.
Their study, published in the New England Journal of Medicine, indicated that patients assigned trimethoprim-sulfamethoxazole (TMP-SMX) had a higher cure rate than those given placebo. The TMP-SMX group also experienced lower rates of subsequent surgical drainage procedures, skin infections at new sites, and similar infections in household members in the weeks after treatment. The findings improve upon the traditional teaching that surgical drainage is the only treatment required for most skin abscesses, according to researcher Gregory J. Moran, MD, clinical professor of emergency medicine at the David Geffen School of Medicine at UCLA and chief of the department of emergency medicine at Olive View-UCLA Medical Center.
“Our findings will likely result in patients more often being recommended to take antibiotics in addition to having surgical drainage when they get a skin abscess,” Moran said in a news release.
Study follows increase in infections
Moran and colleagues conducted a randomized trial from April 2009 to April 2013 at five hospital EDs in Baltimore; Kansas City, Missouri; Los Angeles; Philadelphia; and Phoenix. The study came on the heels of a nearly threefold rise in ED visits for skin and soft-tissue infections (SSTIs) in the U.S. between 1993 and 2005, due mostly to an increase in abscess incidence. During the same period, MRSA emerged as the most common cause of purulent SSTIs in many parts of the world, according to Moran and colleagues.
The researchers sought to compare TMP-SMX — an inexpensive and commonly prescribed antibiotic for SSTIs — to placebo in outpatients aged older than 12 years who had an uncomplicated skin abscess treated with drainage. The study, which included 1,247 patients, was larger than previous investigations that did not show a benefit of antibiotic treatment. Larger studies are required to show relatively small differences in cure rates because drainage alone is successful more than 80% of the time, Moran and colleagues wrote.
Findings herald potential benefits
Patients were assigned twice-daily doses of TMP-SMX (320 mg and 1,600 mg, respectively) or placebo for 7 days and evaluated up to 9 weeks of follow-up. Among the 1,057 patients who qualified for the per-protocol population, 524 were assigned TMP-SMX and 533 were given placebo. Of those assigned TMP-SMX, 92.9% were cured compared with 85.7% in the placebo group (difference, 7.2%; 95% CI, 3.2-11.2). Among the patients in the per-protocol population, those who took TMP-SMX also experienced better secondary outcomes, including:
- a 3.4% rate of subsequent surgical drainage, 5.2% less than the placebo group (95% CI, –8.2 to –2.2);
- a 3.1% rate of skin infections at new sites, 7.2% less than the placebo group (95% CI, –10.4 to –4.1); and
- a 1.7% rate of infections in household members, 2.4% below the placebo group (95% CI, –4.6 to –0.2).
Moran and colleagues wrote that TMP-SMX appears “safe, and is associated with a high cure rate of the primary lesion,” and “offers the possibility of lower rates of costly subsequent medical visits, surgeries, and hospitalizations and of new infections among patients and their household contacts.” – by Gerard Gallagher
Disclosure: Moran reports receiving grant support from Cempra and Durata Therapeutics and being a co-author of a manuscript about a clinical trial of a drug owned by Cubist Pharmaceuticals. Please see the full study for a list of all other authors’ relevant financial disclosures.
Perspective
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Michael S. Calderwood, MD, MPH
Incision and drainage (I&D) alone without an adjunctive antibiotic has been the recommendation for patients with normal host defenses who present with purulent skin and soft tissue infections and no signs or symptoms of systemic infection. The recent paper by Talan and colleagues, however, calls this common clinical teaching into question. They conducted a multicenter, double blind, randomized trial with standardized training of trial personnel on technique and procedures for I&D. After I&D of a skin abscess, patients were randomly assigned to receive 7 days of trimethoprim-sulfamethoxazole (equivalent of two DS tablets by mouth, twice daily; n = 636) or 7 days of placebo (n = 629). Of these, 81% in the treatment arm and 80% in the placebo arm met per-protocol criteria of receiving at least 75% of the doses.
The first thing to note from the study is that I&D alone was often successful (cure rate, 74%). Second, as would be expected with skin abscesses, Staphylococcus aureus was found in 62% of patients (ratio of MRSA to MSSA, 2.8 to 1), with streptococcal species found in only 5% of patients. Almost all of the MRSA were USA 300 community-associated MRSA, and 97% were susceptible to TMP-SMX.
The primary outcome looked at cure rates, with 81% in the treatment arm and 74% in the placebo arm achieving clinical cure, in the modified intention-to-treat analysis (P = .005). In the per-protocol analysis, clinical cure was achieved in 93% of those in the treatment arm, although oddly the cure rate in the placebo arm also increased (P < .001).
In my opinion, the secondary outcomes were more important, with a 60% reduction in subsequent surgical drainage, a 70% reduction in skin infections at new sites, and a 59% reduction in infections among household members, in the per-protocol analysis. There were no differences in invasive infections, which were extremely rare (0.3%).
The authors argue the TMP-SMX is inexpensive and safe and should be prescribed following I&D of skin abscesses. One must be careful, however, to think about the impact that this might have on TMP-SMX resistance in the community, understanding that incision and drainage alone was still able to achieve relatively high clinical cure rates.
Reference:
Stevens DL, et al. Clin Infect Dis. 2014;doi:10.1093/cid/ciu296.
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