Daptomycin plus beta-lactam combination therapy for methicillin-resistant Staphylococcus aureus bloodstream infections: a retrospective, comparative cohort study.

BACKGROUND: Mounting evidence suggests the addition of a beta-lactam (BL) to daptomycin (DAP) results in synergistic in vitro activity against methicillin-resistant Staphylococcus aureus (MRSA) and bolsters the innate immune response to infection. The objective of this study was to provide clinical translation to this experimental data and determine if DAP+BL combination therapy results in improved clinical outcomes compared to treatment with DAP alone in patients with MRSA bloodstream infections (BSI). METHODS: This was a retrospective, comparative cohort study conducted at two academic medical centers between 2008 and 2018. Adults with MRSA BSI treated with DAP for ≥72 hours and initiated within five days of culture collection were included. Patients who received a BL for ≥24 hours and initiated within 24 hours of DAP comprised the DAP+BL group. The primary outcome was composite clinical failure (60-day all-cause mortality and/or 60-day recurrence). Analyses were adjusted for confounding using inverse probability of treatment weighting (IPTW). RESULTS: A total of 229 patients were included (72 DAP+BL and 157 DAP). In unadjusted and IPTW-adjusted analyses, DAP+BL was associated with significantly reduced odds of clinical failure (OR 0.362, 95% CI 0.164, 0.801; aOR 0.386, 95% CI 0.175, 0.853). Adjusted analyses restricted to pre-specified subgroups based on infection complexity and baseline health status, were consistent with the main analysis. CONCLUSIONS: The addition of a BL to DAP was associated with improved clinical outcomes in patients with MRSA BSI. This study provides support to ongoing and future studies evaluating the impact of combination therapy for invasive MRSA infections.