Antibiotics in the Treatment of Smaller Abscesses

Background

Skin and soft tissue infections (SSTI), specifically skin abscesses, are an increasingly common cause for emergency department (ED) visits. Many of these are uncomplicated and are treated in the ED with incision and drainage (I&D) and then discharged. In an era of increasing rates of methicillin-resistant staph aureus (MRSA), there may be a role for adjunct therapy with oral antibiotics to improve cure rates. Previous studies addressing this question have only included small study group sizes and did not demonstrate a benefit of antibiotic treatment. Because of this, practice guidelines for abscess treatment currently recommend that drainage alone is sufficient for treatment and that adjunctive therapy with antibiotics is only necessary in patients who are immunocompromised, diameter >5cm, have surrounding cellulitis, and signs of systemic inflammatory response syndrome (SIRS). 

However, one recent large randomized controlled trial (RCT) showed that healthy outpatients >12 years of age with uncomplicated skin abscesses treated with I&D and trimethoprim-sulfamethoxazole (TMP-SMX) had a higher cure rate than those treated with I&D and placebo, which supports a role for antibiotic therapy (Talan 2016). This study did not evaluate treatment in children less than 12 years of age, compared only placebo to TMP-SMX and did not evaluate other antibiotics that treat MRSA.

Primary Results

Primary Results:

• 786 participants (505 adults, 281 children, mean age 25.5 years)
• 67% of patients had S. aureus, 49% had MRSA

Critical Results:

Clinical cure at the test-of-cure visit in the intention-to-treat population (Primary Outcome)

	Clindamycin	TMP-SMX	Placebo
All Participants Cure Rate	83.1% (78.3 – 87.9)	81.7% (76.8-86.7)	68.9% (62.9-74.9)
Children Cure Rate	89.1% (82.5-95.7)	82.4% (74.0-90.8)	68.5% (58.3-78.7)
Adult Cure Rate	79.4% (72.9-85.9)	81.4% (75.3—87.5)	69.0% (61.8-76.3)
MRSA isolated	81.7 (75.0-88.4)	84.6 (78.0-91.2)	62.9 (53.7- 72.2)
MSSA isolated	89.1 (79.0-99.2)	79.6 (67.3- 91.9)	65.9 (50.8-81.1)
1 Month follow-up	78.6	73.0	62.6
Treatment Related Adverse Events	21.9%	11.1%	12.5%
Area of Surrounding Erythema (cm2)	26.85 +/- 104.34	29.68 +/- 93.76	25.76 +/- 53.11

• The cure rate in the placebo group was significantly lower than that in the clindamycin group (P<0.001) and that in the TMP-SMX group (P<0.001)
• The difference between the cure rate in the TMP-SMX group and that in the clindamycin group was not significant (−P=0.37)
• The results were similar for the population that could be evaluated analysis with significantly different cure rates for placebo versus either antibiotic but no significant difference between clindamycin and TMP-SMX
• Children had a significantly higher cure rate with clindamycin than with placebo or with TMP-SMX, while this difference was not significant in the adult population
• No significant difference in surrounding erythema between treatment arms

Adverse Events

• Most adverse events were mild or moderate and resolved without intervention or sequela
• No c. diff infections reported

Strengths

• Addressed a simple, clinically relevant question with a patient centered outcome
• Randomization and blinding were appropriately performed
• Large, multicenter study throughout different geographical regions of the United States
• Appropriately powered for the primary outcome

Limitations

• Only evaluated two antibiotics that treat MRSA (for example, did not include doxycycline)
• Follow-up was short-term and ended at 1 month
• Variability in I&D skills among ED providers in the study leading to possibility of incomplete drainage and treatment failure
• Patients had moderately sized overlying erythema raising the question of whether clinicians were treating cellulitis (which is widely accepted as requiring antibiotics)

Author's Conclusions

“As compared with incision and drainage alone, clindamycin or TMP-SMX in conjunction with incision and drainage improves short-term outcomes in patients who have a simple abscess. This benefit must be weighed against the known side-effect profile of these antimicrobials.”

Our Conclusions

After I&D of small uncomplicated abscesses in healthy patients with overlying cellulitis, an adjunct course of oral antibiotics with activity against MRSA (clindamycin or TMP-SMX) appears to increase short-term cure rates. In particular, when treating children, clindamycin has a higher cure rate than TMP-SMX or placebo. Clindamycin had lower rates of recurrence of infection at one month when compared to TMP-SMX.

Potential Impact To Current Practice

The findings of this study show strong evidence that antibiotic therapy, in addition to I&D, leads to higher cure rates for small abscesses with overlying cellulitis. These findings should not be taken to mean that all patients with abscesses who are I&D’d in the ED will need antibiotics as the majority of abscesses will resolve with I&D alone. The increased clinical cure rate must be weighed against the potential risks associated with increase antibiotic use such as adverse medication-related events and increasing antibiotic resistance.

Bottom Line

ED providers should consider adjunctive therapy with oral antibiotics with MRSA coverage after I&D of simple, small (<5cm) abscesses with overlying cellulitis in healthy individuals to increase short-term cure rates. There may be an additional benefit of clindamycin over TMP-SMX when treating children. Providers should refer to their local antibiograms for more specific antibiotic recommendations against MRSA. The presence of significant overlying cellulitis continues to warrant adjunctive therapy with antibiotics.

Read More

REBEL EM: Trimethoprim-Sulfamethoxazole for Uncomplicated Skin Abscesses

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Core EM: Incision and Drainage of Cutaneous Abscesses

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References

Talan D et al. Trimethoprim-Sulfamethoxazole versus Placebo for Uncomplicated Skin Abscess. NEJM 2016; 374:823-32. PMID: 26962903