Background: Antibiotic beads are commonly used to treat osteomyelitis, but many of the antibiotic beads, which are
custom-made, are left unused after preparation.

Objective: To compare the inhibitive effectiveness against MRSA of vancomycin and fosfomycin beads sterilized with gamma irradiation and ethylene oxide after 6 and 12 months of storage.

Materials and Methods: In this in vitro study, antibiotic beads were made locally from a mixture of 40 grams of polymethylmethacrylate and 4 grams of an antibiotic, either vancomycin or fosfomycin, using sterile techniques. Six groups of antibiotic beads were prepared including three groups made with vancomycin (a control group, a group sterilized with gamma radiation, and a group sterilized with ethylene oxide) and a similar set of three groups made with fosfomycin. All beads were placed
in sterile packages at room temperature (24 to 37°C) and the sterilized bead groups were stored for either 6 or 12 months. After storage, the beads from each of the six groups were tested for
inhibitive effectiveness against MRSA using a modified disc diffusion technique for 6 weeks.

Results: After 12 months of storage, there was no statistically significant difference in inhibitive effect against MRSA among the six groups: the control group and the two sterilized groups (gamma radiation and ethylene oxide) with beads made of either vancomycin or fosfomycin.

Conclusion: Either gamma radiation or ethylene oxide can be used as a sterilization method for antibiotic beads against MRSA without deterioration in inhibitive effect after 12 months of storage. The inhibitive effect of antibiotic beads against MRSA sterilized with either gamma radiation or with ethylene oxide is not reduced after 12 months of storage.

Keywords: Antibiotic beads, Sterilization, Gamma radiation, Ethylene oxide, MRSA