Abstract
Water-soluble Estracyt® and water-insoluble estradiol-17βwere charged into a pig ureter which was used as a device for drug delivery system. The devices containing drugs were implanted subcutaneously in the back of male Wistar rats for 8 weeks at maximum and the release profiles of drugs from the device were checked in both the in vitro and in vivo experiments. The daily doses of drugs released in vitro from the device were kept constant at rates of 0.054mg/day for Estracyt® and 0.029mg/day for estradiol-17β. However, the daily doses of drugs released in vivo from the same device significantly decreased with an increase in implantation period. This can be easily explained from the results described below. E. g., the cumulative amounts of Estracyt® released in vitro and in vivo from the device for a period of 4 week from start of the test were found to be 1.513 and 0.399mg, respectively, while those amounts released during the first 8 weeks period were to be 3.240 and 0.448mg, respectively, in the above order. In order to claer the cause of such a retardation of in vivo release, the mutual interaction between the rat tissue and the device was microscopically investigated.
