Level 2 [mid-level] evidence

Skin infections are one of the most common types of infection worldwide, affecting persons of all ages and geographies. The incidence of abscesses and cellulitis appears to be increasing in the United States, where methicillin-resistant Staphylococcus aureus (MRSA) has been identified as the leading cause of skin abscesses, furuncles, and carbuncles (Arch Intern Med. 2008;168[14]:1585; BMC Infect Dis. 2013;30;13[1]:252).

Suspected community-acquired MRSA is often treated with clindamycin or trimethoprim-sulfamethoxazole (TMP-SMX, also known as co-trimoxazole), but certain strains of MRSA may have inducible clindamycin resistance. The potential for inducible resistance may influence some clinicians to prefer TMP-SMX for potential MRSA infections.

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In addition, clindamycin has a relatively higher cost and increased risk of C. difficile infection, which along with local resistance patterns may all be factors in clinical decision making. A recent randomized trial compared clindamycin 150 mg three times daily vs. TMP-SMX 160mg/800 mg twice daily for 10 days in 524 patients (mean age, 27 years) with uncomplicated skin infections including cellulitis, abscesses greater than 5 cm in diameter, or both (N Engl J Med. 2015;372[12]:1093).

Of the 524 patients enrolled, 29.6% were children. The presenting infection included cellulitis in 53.4%, abscess in 30.5%, and a mixed infection defined as one or more abscesses plus one cellulitis lesion in 15.6%. All abscesses had incision and drainage before administration of antibiotics. Cultures were prepared from samples taken from 56.5% of patients, and S. aureus was isolated in 73.3% of cultures (77% of which were identified as MRSA).

Overall, there was no significant difference in the clinical cure rate between days 7 and 10 of treatment comparing clindamycin vs. TMP-SMX, with clinical cure in 80.3% of patients with clindamycin and 77.7% of patients with TMP-SMX. In a subgroup analysis of patients with cellulitis without abscess, clindamycin was associated with a cure rate of 80.9%, compared with 76.4% with TMP-SMX (not significant). There were also no significant differences in the cure rate at seven to 10 days for patients with abscess, the overall clinical cure rate at one month, or adverse events. 

The results of this trial suggest that clindamycin and TMP-SMX appear equally effective for treating uncomplicated skin infections in adults and children. Previous studies have suggested, however, that systemic antibiotics after incision and drainage of uncomplicated skin abscesses may not increase the clinical cure rate (Emerg Med J. 2013 May 18), thus many patients in this trial may have achieved clinical cure without antibiotics.

The Infectious Diseases Society of America (IDSA) recommends incision and drainage with complete evacuation of all purulent material as primary therapy for skin abscesses and only recommends systemic antibiotics for patients with an impaired immune system or signs of a systemic inflammatory response. IDSA also recommends antimicrobial agents active against streptococci as first-line treatment for patients with cellulitis, unless patients have risk factors for MRSA or symptoms of systemic inflammatory response syndrome, as streptococcal species seem to be the most common cause of cellulitis (Medicine [Baltimore]. 2010;89[4]:217; Clin Infect Dis. 2008;46[6]:855).

The subgroup analysis of patients presenting with cellulitis without abscess suggests that clindamycin might have a slightly higher clinical cure rate compared with TMP-SMX in this population, but this subgroup comparison is likely underpowered to detect statistically significant differences.

Alan Ehrlich, MD, is a deputy editor for DynaMed, in Ipswich, Mass., and assistant clinical professor in Family Medicine, University of Massachusetts Medical School in Worcester.

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