Drug release from a novel self‐setting bioactive glass bone cement containing cephalexin and its physicochemical properties

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Abstract
A novel device containing cephalexin as a model drug using a self‐setting bioactive cement based on CaOSiO2P2O5 glass was investigated. The device consisted of 95 wt/wt% glass powders and 5 wt/wt% cephalexin powder hardened within 5 min after mixing with a phosphate buffer. After setting, in vitro drug release from homogeneous orheterogeneous drug‐loaded cement pellets in a simulated body fluid (SBF) at pH 7.25 and 37°C continued for over 4 weeks. The hardened cement gradually formed low‐crystallinity hydroxyapatite with high bioactivity in hard bone tissue and reduced in volume by about 5% during dissolution testing in SBF. Consequently, 30% of the loaded drug was squeezed from the cement system at the initial stage of the drug release, and the remainder released more slowly. Because the heterogeneous system consisting of the cement and drug‐loaded pellet avoided the drug‐squeezing effect, it showed a longer drug release term than the homogeneous drug‐loaded cement. The heterogeneous system using the hardened cement after soaking in SBF at 37°C for 10 days showed very slow drug release at the initial stage because it completely avoided the drug‐squeezing effect, and the release was a zero‐order pattern. © 1995 John Wiley & Sons, Inc.