Subgroup Analysis of Antibiotic Treatment for Skin Abscesses

Study objective: Two large randomized trials recently demonstrated efficacy of methicillin-resistant Staphylococcus aureus (MRSA)-active antibiotics for drained skin abscesses. We determine whether outcome advantages observed in one trial exist across lesion sizes and among subgroups with and without guideline-recommended antibiotic indications. Methods: We conducted a planned subgroup analysis of a double-blind, randomized trial at 5 US emergency departments, demonstrating superiority of trimethoprim-sulfamethoxazole (320/1,600 mg twice daily for 7 days) compared with placebo for patients older than 12 years with a drained skin abscess. We determined between-group differences in rates of clinical (no new antibiotics) and composite cure (no new antibiotics or drainage) through 7 to 14 and 42 to 56 days after treatment among subgroups with and without abscess cavity or erythema diameter greater than or equal to 5 cm, history of MRSA, fever, diabetes, and comorbidities. We also evaluated treatment effect by lesion size and culture result. Results: Among 1,057 mostly adult participants, median abscess cavity and erythema diameters were 2.5 cm (range 0.1 to 16.0 cm) and 6.5 cm (range 1.0 to 38.5), respectively; 44.3% grew MRSA. Overall, for trimethoprim-sulfamethoxazole and placebo groups, clinical cure rate at 7 to 14 days was 92.9% and 85.7%; composite cure rate at 7 to 14 days was 86.5% and 74.3%, and at 42 to 56 days, it was 82.4% and 70.2%. For all outcomes, across lesion sizes and among subgroups with and without guideline antibiotic criteria, trimethoprim-sulfamethoxazole was associated with improved outcomes. Treatment effect was greatest with history of MRSA infection, fever, and positive MRSA culture. Conclusion: Treatment with trimethoprim-sulfamethoxazole was associated with improved outcomes regardless of lesion size or guideline antibiotic criteria.