Drug release into hydrogel-based subcutaneous surrogates studied by UV imaging.

Upon subcutaneous administration, the distribution of drug between the delivery vehicle and the biological tissue critically affects the absorption of drug substances. Utilization of physical models resembling the native tissues appears promising for obtaining a detailed understanding of the performance of drug delivery systems based on in vitro experiments. The objective of this study was to evaluate a UV imaging-based method for real-time characterization of the release and transport of piroxicam in hydrogel-based subcutaneous tissue mimics/surrogates. Piroxicam partitioning from medium chain triglyceride (MCT) into 0.5% (w/v) agarose or 25% (w/v) F127-based hydrogels was investigated by monitoring the concentration profiles of the drug in the gels. The effect of pH on piroxicam distribution and diffusion coefficients was studied. For both hydrogel systems, the diffusion of piroxicam in the gels was not affected significantly by the pH change from 4.0 to 7.4 but a considerable change in the oil-gel distribution coefficients was found (24 and 34 times less at pH 7.4 as compared those observed at pH 4.0 for F127 and agarose gels, respectively). In addition, the release and transport processes of piroxicam upon the injection of aqueous or MCT solutions into an agarose-based hydrogel were investigated by UV imaging. The spatial distribution of piroxicam around the injection site in the gel matrix was monitored in real-time. The disappearance profiles of piroxicam from the injected aqueous solution were obtained. This study shows that the UV imaging methodology has considerable potential for characterizing transport properties in hydrogels, including monitoring the real-time spatial concentration distribution in vitro after administration by injection.