Doctors have been taught that drainage is sufficient for treatment of a simple skin abscess and that antibiotics are not indicated. In fact, antibiotic use in this situation has become the target of some antibiotic stewardship hawks and providers have been shamed for their inappropriate prescriptions.
There were reasons for this based first on the observation that the cure rate with drainage alone was over 80% and even supported by some randomized placebo-controlled trials. Actually, when I was asked to write an accompanying editorial about one of those trials, my title was, “Lack of Antibiotic Efficacy…” But my point at that time was that because the existing studies were too small and flawed to draw conclusion, the matter had not come to a head. I know, a bad pun.
Better outcomes with antibiotics
In the March 3, 2016 issue of the New England Journal of Medicine, my colleagues and I present by far the largest trial of 1265 subjects that challenges the dogma that antibiotics are ineffective for drained skin abscesses. In this trial, emergency department (ED) patients with a skin abscess at least 2 cm (cavity size), which was drained in the ED, were randomized to trimethoprim-sulfamethoxazole (2 DS BID) or identical placebo for 7 days. Subjects were followed 6-8 weeks after treatment. The median abscess cavity size was 2.5 cm and the median maximal length of associated erythema (redness) was 7 cm, although some lesions were very large. We found that in the population that returned for follow-up and complied with their medication, the abscess cure rate in the antibiotic group was about 93% compared to 86% in the placebo group, a statistically significant difference of 7 percentage points.
If we look at what we called the composite cure rate (i.e., not either requiring a new antibiotic treatment or an additional surgical drainage procedure), the difference was 12 percentage points in favor of the antibiotic group, 86% vs. 74%. The benefit of antibiotic treatment extended to other secondary outcomes as well. The antibiotic group had fewer recurrent infections, surgeries, hospitalizations, and disability and analgesic use days. Remarkably, household members of patients who took antibiotics also had fewer infections than of those who got the placebo.
What are the downsides of antibiotic treatment?
One would think that this would be strong and convincing evidence to now prescribe antibiotics for a drained skin abscess. But, let’s consider the potential downside of treating with antibiotics:
- There is cost, but in this case, it’s small, very small—about $5 for the whole course.
- Antibiotics have side effects. But, in our study, we observed no serious side effects (e.g., Stevens-Johnson Syndrome or C. difficile colitis) and only slightly more mild, mostly gastrointestinal, side effects associated with trimethoprim-sulfamethoxazole. Remember, the comparison is a sugar pill. However, we should acknowledge that this antibiotic can rarely cause serious complications and has important drug interactions, like with Coumadin.
- There’s the theoretical concern about overuse of antibiotics promoting bacterial resistance. This is not what I would view as a high-risk circumstance to see the development of resistance since these are a few easily-targeted patients with a definite bacterial infection (not all young children with a fever or adults with bronchitis) who are mostly healthy and going back to their individual homes with other generally healthy people and being treated for a defined short-course.
So one would think the answer was pretty clear. But there will still be naysayers who will not offer antibiotic treatment to patients because they feel that the cure rate with drainage alone is high enough—for them. However, let’s look at this also from the perspective of the person who has the infection.
The patient’s perspective
Although some of the abscesses in our study were small, considering that they must have been bad enough for these patients to drag themselves into an ED. Many primary care providers don’t have the time, training, or equipment to do incision and drainage in their office. So now, after draining the abscess, and likely generating a bill to the patient of over $1000, despite clear evidence of outcome benefits, some providers would neither recommend nor offer an antibiotic—one that costs $5?
Let’s says we were the patient’s investment counselor or Las Vegas bookie. Most people can spare an extra $5. On average, what would that $5 buy? Let’s assume the 7 percentage point increase in abscess cure rate with antibiotics. That means that for $5, the patient has a 1 in 14 chance of avoiding another medical visit because their infection did not cure (but would have if they had been given antibiotics). The minimal cost of a medical visit might be $200 for an office visit and much more if the patient has to return to the ED. So 1/14th of $200 is $14. The patient is already ahead $9.
If the secondary outcome findings mentioned above are valid, there are additional savings of avoiding surgeries, hospitalizations, and recurrent infections in the placebo group. If the patient lives in a crowded house or plays with an NFL team, antibiotics will help prevent infection in the person’s contacts. I know how upset I would be if Aaron Rodgers was sidelined after contracting an abscess on his throwing hand from his center who had a buttock abscess that was only drained and not treated with trimethoprim-sulfamethoxazole.
There may be types of patients who benefit more or less from antibiotics and we plan to do subgroup analyses which may be the basis for future validation studies. For example, patients with small abscesses may benefit less, those with recurrent infections may benefit more, but we do not know this yet. In this age of shared decision-making, we should consider that, for some people, the cost and inconvenience of a return visit to a doctor are high, and there are others with multiple drug sensitivities who may wish to avoid any chance of an adverse drug reaction.
The evidence has reached a point now (whoops, another pun) that providers can spell out the costs, potential advantages and few disadvantages of antibiotic treatment, and help their patients decide which course they prefer.
If you are interested in this topic, then you may want to review a case vignette in today’s New England Journal of Medicine and vote as to your preferred treatment approach.