APRIL 2012 |฀Volume฀35฀•฀Number฀4 n Feature Article abstract Full article available online at Healio.com/Orthopedics. Search: 20120327-19 Antibiotics are commonly mixed with polymethylmethacrylate (PMMA) cement to suppress severe periprosthetic infections associated with total joint arthroplasty. The relationship between antibiotic concentration and the resulting elution kinetics re- mains unclear. The purpose of this study was to characterize the release of daptomycin from PMMA cement and the subsequent effects on mechanical properties. Varying concentrations of daptomycin and tobramycin were vacuum mixed in commer- cially available PMMA and subjected to an in vitro elution period. High-performance liquid chromatography was used to quantify the concentration of the amount of dap- tomycin eluted at predetermined time points. Samples were subjected to compres- sive loading to analyze the effect of antibiotic concentration on cement mechanical properties. Daptomycin elution increased when initial tobramycin concentration was increased. Furthermore, the addition of antibiotics increased the compressive strength of the cement in the postelution period. The binary addition of tobramycin with dap- tomycin antibiotics modifies the elution and mechanical properties of PMMA bone cement. Based on the findings of our study, 2 g of daptomycin and 3.6 g of tobramycin per 40-g packet of cement should be used to promote daptomycin elution without sacrificing PMMA mechanical properties. Drs Kaplan and Verner are from the Department of Orthopaedic Surgery, and Mr Kurdziel and Dr Baker are from the Department of Orthopaedic Research, Beaumont Health System, Royal Oak, Michigan. Drs Kaplan, Baker, and Verner and Mr Kurdziel have no relevant financial relationships to disclose. Beaumont Health System’s Research Institute provided funding for the completion of this study. Correspondence should be addressed to: Kevin C. Baker, PhD, Department of Orthopaedic Research, Beaumont Health System, 3811 W 13 Mile Rd, Ste 404, Royal Oak, MI 48073 (kevin.baker@ beaumont.edu). doi: 10.3928/01477447-20120327-19 Characterization of Daptomycin-loaded Antibiotic Cement LIGE KAPLAN, MD; MICHAEL KURDZIEL, MS; KEVIN C. BAKER, PHD; JAMES VERNER, MD infection SPOTLIGHT ON Figure: Cumulative release of daptomycin for groups containing 1.0 g (A) and 2.0 g (B) of dapto- mycin mixed with varying amounts of tobramycin throughout 96 hours of elution. A B e503