Podcast #52 - Big or Small, Abscesses Improve with Antibiotics

We have talked about abscess management before both here (Podcast #13) and on the Skeptics' Guide to Emergency Medicine (Podcasts #156 and #164).   Even though we have talked about using antibiotics before, there has been debate on its use in smaller abscesses.  Today, we cover how antibiotics are still beneficial even for the small ones given the most recent evidence out there.  Listen to podcast and read this blog for all the details as we cover different points in each.

Title:
A Placebo-Controlled Trial of Antibiotics for Smaller Skin Abscesses
 
Case:
A 34 y/o male with no past significant medical history presents complaining of a skin abscess that has been present for two days.  He is afebrile and denies any known drug allergies.  On exam you note a 4cm diameter area of erythema and swelling that is warm to the touch.  Ultrasound confirms this to be an abscess (similar to the image above from Mount Sinai EM Ultrasound's page).  After incision and drainage, you are trying to decide if this patient needs antibiotics.  You know the two most common are clindamycin and trimethoprim-sulfamethoxazole (TMP-SMX).  However, you do not know if either is needed or which one may be better.
 
Background:
Skin abscess are a common complaint across healthcare and a frequent presentation to emergency departments across the world.  Staph infections are the most common cause for these infections.  Clindamycin and TMP-SMX are frequently used given their low cost along with their safety and efficacy.  A recent trial by Talan et al found TMP-SMX in larger abscesses had a higher cure rate than incision and drainage alone.  Other studies have done the same for larger abscesses both with clindamycin and TMP-SMX with similar findings for both but did not include a placebo or smaller sized abscesses. 
 
Clinical Question:
Does clindamycin or TMP-SMX in conjunction with incision and drainage improve short-term outcomes in patients with a simple abscess compared with incision and drainage alone?
 
Reference:

• Population: Patients 6 months of age or older with a single abscess less than 5cm in diameter if over 8 years old (smaller if younger based on other criteria) evidence by two or more of the following signs or symptoms for at least 24 hours: erythema, swelling or induration, local warmth, purulent drainage, and tenderness to pain or palpation.      
  • Exclusion Criteria: Patients with superficial skin infections, infection at a body site requiring specialized management, human or animal bite, oral temperature higher than 38.5°C (or 38°C for children 6 to 11 months of age), presence of SIRS, immunosuppressive therapy or an immunocompromised condition, BMI greater than 40, surgical site or prosthetic device infection, or systemic anti-staphylococcal antibiotics in the previous 14 days.  They were also ineligible if they required hospitalization, lived in a long-term care facility, had cancer or an inflammatory disorder treated in the previous 12 months, or had major surgery in the previous 12 months.
• Intervention: Incision and drainage with either 300mg total of clindamycin three times daily or TMP-SMX as a total of 800/160 twice daily (with placebo in between those two doses). 
• Comparison: Incision and drainage with placebo taken three times daily.
• Outcome: Clinical cure 7 to 10 days after the end of treatment.

 
Author’s Conclusions:
As compared with incision and drainage alone, clindamycin or TMP-SMX in conjunction with incision and drainage improves short-term outcomes of patients who have a simple abscess.  The benefit must be weighed against the known side-effect profile of these antimicrobials.
 
Quality Checklist for Randomized Clinical Trials:

1. The study population included or focused on those in the ED. Yes
2. The patients were adequately randomized. Yes
3. The randomization process was concealed. Yes
4. The patients were analyzed in the groups to which they were randomized. Yes
5. The study patients were recruited consecutively (i.e. no selection bias). Yes
6. The patients in both groups were similar with respect to prognostic factors. Yes
7. All participants (patients, clinicians, outcome assessors) were unaware of group allocation. Yes, with the exception of research pharmacists who determined the correct dosing
8. All groups were treated equally except for the intervention. Yes
9. Follow-up was complete (i.e. at least 80% for both groups). Yes
10. All patient-important outcomes were considered. Yes
11. The treatment effect was large enough and precise enough to be clinically significant. Yes

 
Key Results:
​A total 786 patients were randomized with 505 being adults and 281 being children.  266 patients were assigned to receive clindamycin, 263 to receive TMP-SMX, and 257 received a placebo.  Using the intention-to-treat population, the cure rate at 10 days was 221 in the clindamycin group (83.1%), 215 in the TMP-SMX group (81.7%), and 177 in the placebo group (68.9%) with a significant difference between antibiotics versus placebo (P<0.001).
 
Key Points of Debate:

• The NNT was most impressive when treating Staphlycoccus aureus species.
  • In general, the NNT when using antibiotics to obtain a clinical cure versus placebo was 7.4 in this study.
  • When treating for all Staphlycoccus aureus species, the NNT was 5.1 which was 4.6 in TMP-SMX for MRSA and 4.3 for clindamycin and MSSA.
  • These findings show a clinical benefit of antibiotic therapy in addition to incision and drainage seems to be limited to patients with Staphlycoccus aureus infections.
• There were some major pros and cons to clindamycin.
  • In cases of resistance to clindamycin, cure rates were the same whether or not they got antibiotics for their abscess.
  • Of the 13 participants with Staphlycoccus aureus that were resistant to clindamycin, one found resistance by disk diffusion (D-zone) testing
  • Treatment associated adverse effects were almost double that with clindamycin compared to TMP-SMX or placebo.
  • Using clindamycin led to the rate of recurrence being half that of placebo or TMP-SMX
  • Clindamycin was also found to work better than TMP-SMX in the treatment of abscesses in children.
• TMP-SMX also has its own pros and cons.
  • A lower dose of TMP-SMX was used in this study with the standard “double dose” in this study for 10 days versus the “quadruple dose” for seven days from the previous study of benefit showing that this dose which is more commonly used is also effective.
  • There was no resistance to TMP-SMX in this study.
  • Serious adverse events were mostly similar with only one being related to the antibiotic and that was with TMP-SMX (a hypersensitivity reaction that fully resolved) which demonstrates that it is also not without its risks.
• Although this study used two of the most common antibiotics, there are other potentially beneficial antibiotics that could be used.
  • Doxycycline is used in some facilities more frequently and is active against MRSA.
  • However, there are limitations especially in pediatric use as it is contraindicated in those less than 8 years of age.

 
Comparing Conclusions:
We agree that antibiotics (specifically clindamycin or TMP-SMX) improve short-term outcomes in patients with a simple small abscess that has undergone incision and drainage versus having an incision and drainage alone.
 
Our Bottom Line:
Even for small abscesses, antibiotics can be beneficial for the treatment of abscesses with incision and drainage especially in cases of Staphlycoccus aureus infections.
 
Case Resolution:
After completing the incision and drainage, you discuss with the patient the risks, benefits, and potential complications of antibiotics.  With shared decision making, he agrees to antibiotics and you prescribe him medications before he is discharged.
 
Clinical Application:
Antibiotics are becoming more frequently used for the treatment of abscesses after incision and drainage.  This study further supports the growing use of antibiotics whether for small or large abscesses.  However, given its low NNT especially in Staphlycoccus aureus infections, this is a beneficial treatment overall.  It is worth remembering that antibiotics are not without risks and should be carefully considered.
 
What do I tell my patient?
Antibiotics have been shown to be helpful in treating abscesses in addition to opening up the abscess through an incision and drainage, especially in the staph type infections we often see.  These are usually well tolerated but there are some risks such as allergic reactions but it is more often mild symptoms such as nausea and diarrhea.
 
Conclusion:
Thank you for listening to the podcast and reading the blog.  Please let us know what you think by giving us feedback here in the comments section or contacting us on Twitter or Facebook.  Remember to look us up on Libsyn and on iTunes.  If you have any questions you can also comment below, email at [email protected], or send a message from the page.  We hope to talk to everyone again soon.  ​Until next time, continue to provide total care everywhere.

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