In vitro Elution of Gentamicin From Plaster of Paris Beads

Abstract

Objective—To determine the in vitro elution characteristics of gentamicin from Plaster of Paris–gentamicin (POP‐gent) beads.Study design—In vitro, controlled, experimental study.Methods—The POP‐gent beads were made using a bead mold from 20 g calcium sulfate hemihydrate, 5 mL (500 mg) gentamicin solution, and 3 mL of phosphate buffered saline (PBS). Control beads were made similarly, using 30 g of dried powder and 8 mL of PBS. Beads were left in the mold overnight, gas‐sterilized with ethylene oxide, and stored at room temperature for 5 months before testing. Bead chains were placed in sterile tubes containing porcine serum, and tubes were placed in a 37°C incubator on a rocker. Serum was removed at intervals over 14 days and the concentration of gentamicin determined by fluorescent polarization immunoassay. Serum antibacterial activity was determined against an equine originEscherichia coli.Results—POP‐gent beads released gentamicin for the 14‐day sampling period. Eighty percent of the gentamicin incorporated in the beads was released over the first 48 hours. Eluent from POP‐gent beads inhibited the growth ofE coliat all time periods. No gentamicin was eluted from control beads and control eluent did not inhibit growth ofE coli.Conclusions—In this experimental model, POP‐gent beads released bactericidal drug for 14 days. Eighty percent of the gentamicin incorporated into the beads was released during the first 48 hours. The drug retains its bactericidal activity after ethylene oxide sterilization and storage at room temperature for up to 5 months.Clinical Relevance—Pop‐gent beads may be a useful repository device to deliver gentamicin locally in tissues.