Sol-gel-processed sintered silica xerogel as a carrier in controlled drug delivery

Sol-gel-processed sintered silica xerogel was studied as a controllable, di ssolvable, implantable material. The erosion of the matrix and the release of the preadsorbed drug toremifene citrate was investigated both in vitro a nd in vivo using mice. In an in vitro dissolution study, 50 to 60% of the d rug was released after 24 h, according to the square root of time kinetics, and the weight loss of the silica was 24 wt %. Silica xerogel with tritium -labeled toremifene was implanted subcutaneously in mice for 56 days. To de termine the amount of tritiated drug remaining in the silica disks at the i mplantation site, the disks were excised periodically and the radioactivity measured. About 40% of the radioactivity was released during the first 4 d ays and all of it within 28 days. Radioactivity also was measured in the Li ver, lungs, kidneys, uterus, and blood. The radioactivity reached a maximum level after 4 days in the liver, kidneys, and lungs and slowly decreased u ntil all of the drug had been released from the matrix after 28 days. After release of the drug (28 days) the amount of remaining silica xerogel impla nt was 45 wt %, and at the end of the study (56 days) it was 24 wt %. In th e histopathological study, sintered silica xerogel did not show any tissue toxicity at the site of the implantation, in the liver, or in the kidneys. It was concluded that sintered silica xerogel is a biocompatible and contro llably resorbable material and therefore is a promising matrix for use in t he sustained delivery of drugs. (C) 1999 John Wiley & Sons, Inc.