Vancomycin release behaviour from amorphous calcium polyphosphate matrices intended for osteomyelitis treatment

Calcium polyphosphate (CPP) antibiotic delivery matrices were prepared using a unique processing technique involving the exposure of antibiotic-loaded CPP pastes to high humidity for 0, 5, or 24 h. After the designated gelling period, samples were dried for a minimum of 24 h. At several time points out to 130 h, the elution medium was monitored for vancomycin, Ca2+ ion and ortho and poly phosphate release levels. Vancomycin activity was also assessed after 1, 24 and 130 h, while solution 31P-NMR was used to monitor changes in chain length within a 24 hr gelled VCM disc throughout the elution process. The gelling and drying process significantly reduced the rate of vancomycin release during the initial 2-4 h of elution, while extending the effective antibiotic release period by an additional 80 h. The mild conditions associated with matrix fabrication readily allowed for vancomycin incorporation within an environment that did not disrupt antibiotic activity. Throughout the elution process, all sample groups experienced considerable swelling followed by some apparent bulk erosion. Phosphate chain lysis was clearly observed by the end of the elution period. Generally, no strong or consistent correlation existed between matrix degradation and antibiotic release for the treatment groups investigated. An ability to delay antibiotic release using CPPs in conjunction with this protocol supports further investigations into the potential of this matrix as a localized drug delivery system.