Effects of storage up to 1 year on the in vitro antimicrobial activity of preformulated antibiotic‐impregnated calcium sulfate beads

Abstract

AbstractObjectiveTo compare antimicrobial activity as demonstrated by the zone of inhibition (ZOI) produced by antibiotic‐impregnated calcium sulfate (CaSO4) beads after storage for 0, 3, 6, 9, and 12 months.Study designControlled laboratory study.Sample populationThree‐millimeter diameter CaSO4beads impregnated with vancomycin (125 mg/mL), or amikacin (250 mg/mL), or without antibiotic (control).MethodsCalcium sulfate beads were created at the onset of the study. Individual beads were separated in sterile containers and stored in a closed cabinet at room temperature and humidity for 0, 3, 6, 9, or 12 months until testing. The ZOI against methicillin‐resistantStaphylococcus pseudintermedius,methicillin‐resistantStaphylococcus aureus,andPseudomonas aeruginosawas recorded with serial replating on a fresh lawn of bacteria every 24 h until beads failed to produce a ZOI. The ZOIs and their changes were compared with mixed‐effects linear models. Eluted concentrations of vancomycin measured with high‐performance liquid chromatography were reported.ResultsAt 24 h, ZOIs were comparable regardless of time since formulation, except vancomycin againstP. aeruginosa,which failed to generate a ZOI. The daily changes of ZOI and duration of activity of antibiotics did not vary between storage length (p > .05). There was no consistent change in eluted drug concentration between storage length of beads.ConclusionLight protected storage at room temperature for up to 12 months did not impair the in vitro activity of antibiotic‐impregnated CaSO4beads, as demonstrated through ZOIs.Clinical significanceWhen stored correctly, antibiotic‐impregnated CaSO4beads can be used at least up to 12 months after formulation.