Local Release of Antibiotics for Surgical Site Infection Management Using High-Purity Calcium Sulfate: An In Vitro Elution Study

Abstract Background: The aim of this study was to characterize the elution of four antibiotics from pharmaceutical-grade calcium sulfate beads and show that the eluted antibiotics retained efficacy. Methods: Calcium sulfate was combined with gentamicin, tobramycin, vancomycin, or rifampicin (ratio: 20 g of calcium sulfate, to 240 mg, 500 mg, 900 mg, and 600 mg of antibiotic, respectively). Three grams of beads were immersed in 4 mL of sterile phosphate-buffered saline (PBS) at 37°C. At each time point (4, 8, 24 h; 2, 7, 14, 28, 42 d), eluates were removed for analysis by liquid chromatography–mass spectrometry. The antimicrobial efficacy of antibiotics combined with calcium sulfate beads after 42 d was tested by a modified Kirby-Bauer disc diffusion assay. Results: All samples showed a generally exponential decay in the eluted antibiotic concentration. At the first time point, both gentamicin and tobramycin had eluted to a peak concentration of approximately 10,000 mcg/mL. For rifampicin, the peak concent...