Understanding and Application of Daptomycin-Susceptible Dose-Dependent Category for Enterococcus: A Mixed-Methods Study

Background: In 2018, the Clinical Microbiology Laboratory at our institution adopted updated daptomycin Enterococcus-susceptible dose-dependent breakpoints. While the introduction of susceptible dose-dependent (SDD) was intended to guide practice toward optimal dosing, the understanding and application of daptomycin SDD breakpoints for enterococci were unknown. Methods: This mixed-methods study combined a clinician survey with a retrospective pre-post prescribing analysis. An 8-question survey was distributed to infectious diseases (ID) and internal medicine (IM) clinicians. A retrospective chart review of hospitalized adults with infections due to Enterococcus spp. was conducted before (pre-SDD) and after (post-SDD) adoption of SDD reporting for enterococci. Results: Survey response rates were 40 of 98 (41%) for IM and 22 of 34 (65%) for ID clinicians. ID clinicians scored significantly higher than IM clinicians in knowledge of SDD. Chart review of 474 patients (225 pre- vs 249 post-SDD) showed that daptomycin dosage following susceptibility testing was significantly higher post-SDD compared with pre-SDD (8.5 mg/kg vs 6.4 mg/kg; P < .001) with no difference in empiric dosing (6.3 mg/kg vs 6.2 mg/kg; P = .67). Definitive daptomycin use varied between the pre- and post-SDD periods (35.1% vs 16.9%; P < .001). Conclusions: The survey revealed that ID clinicians placed more importance on and had more confidence in the SDD category over IM clinicians. SDD reporting was associated with a change in definitive daptomycin dosing. ID specialist involvement is recommended in the care of infections due to enterococci for which daptomycin is reported as SDD given their expertise.