Effects of Ethylene Oxide Sterilisation on the In Vitro Antimicrobial Activity of Preformulated Antibiotic-Impregnated Calcium Sulfate Beads

To determine whether the elution of antibiotics from calcium sulfate (CaSO4) beads differs following ethylene oxide gas sterilization compared with their nonsterilized counterparts and whether sterilization affects their antibacterial activity after a period of storage for up to 6 months post curation. Prospective controlled laboratory study. 3 mm diameter CaSO4 beads impregnated with either amikacin, gentamicin, cefazolin, vancomycin, or no antibiotic, each with or without ethylene oxide gas sterilization. Antibiotic-impregnated CaSO4 beads were created at the beginning of the study. Half of the beads underwent gas sterilization and all beads were stored in the clinic until testing. Beads were tested against a clinical strain of Staphylococcus pseudintermedius via Modified Kirby–Bauer agar diffusion assay testing, measuring the zone of inhibition (ZOI) produced every 24 hours for 5 days. Beads were tested at 1 day, 1 week, 1 month, 3 months, and 6 months post curation with or without gas sterilization, and their changes were compared using mixed-effects linear models. Beads sterilized using ethylene oxide showed similar ZOI over 5 consecutive days of elution compared with the nonsterilized beads. Beads that were sterilized and stored for up to 6 months demonstrated similar ZOI to beads that were not sterilized and tested immediately. Gas sterilization followed by storage for up to 6 months post curation did not impair the in vitro activity of antibiotic-impregnated CaSO4 beads when tested against a clinical strain of S. pseudintermedius. Antibiotic impregnated CaSO4 beads can be created in advance, gas sterilized, stored in the clinic and retain antibacterial activity for up to 6 months post curation.