- Kenny Lin, MD, MPH
Cephalexin has long been my oral antibiotic of choice for a patient with uncomplicated cellulitis and no cephalosporin allergy. However, the increasing prevalence of skin and soft tissue infections (SSTIs) caused by community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA), often mistaken by patients and clinicians for spider bites, has raised the question of whether it makes sense to also prescribe an antibiotic such as trimethoprim/sulfamethoxazole for empiric CA-MRSA coverage for immunocompetent patients with cellulitis that is not purulent or severe enough for inpatient therapy.
A 2009 case-control study found that children with SSTIs who received empiric monotherapy with trimethoprim/sulfamethoxazole had higher rates of treatment failure than those who received beta-lactam antibiotics. Although helpful, this study did not measure outcomes in adults or in children who were prescribed more than one antibiotic. Despite the lack of evidence of benefit, national data suggest that up to 3 in 4 patients presenting to the emergency department with skin infections are prescribed antibiotics active against CA-MRSA. Potential downsides of "double coverage" include higher rates of adverse effects, cost, and increasing antibiotic resistance.
In a recent paper in JAMA, Dr. Gregory Moran and colleagues reported the results of a multicenter randomized, controlled trial of 500 adolescents and adults with diagnosed in the emergency department with cellulitis and no wound, purulent drainage, or abscess (verified by soft tissue ultrasound) who received 7 days of therapy with either cephalexin plus trimethoprim/sulfamethoxazole or cephalexin plus placebo. They found no differences in clinical cure rates in either the modified intention-to-treat or per-protocol analyses.
Based on this study's results, I will continue to restrict my use of trimethoprim/sulfamethoxazole to patients whose cellulitis fails to respond to cephalexin and patients with purulent infections. Of note, the American College of Emergency Physicians recommends against sending wound cultures or prescribing antibiotics in persons who undergo successful incision and drainage of skin and soft tissue abscesses and who have adequate medical follow-up. A 2015 AFP article provides more information on the management of SSTIs, including inpatient treatment and other special considerations.