Drug release from calcium and zinc pectinate beads: Impact of dissolution medium composition

The aim of this study was to investigate drug release from calcium and zinc pectinate beads and to understand the impact of medium electrolytes during drug transfer. A potential drug carrier for colonic drug delivery (rutin) was prepared with calcium and zinc pectinate beads and was tested in three different simulated intestinal fluids (pH 7.3) with phosphates (Sorensen's and Mc Ilvaine's buffers) and without phosphates (Tris-buffer). According to swelling studies and zinc ions release, it was showed that zinc ions keep adhering to the bead surface. Drug release and swelling behaviour from the two dosage forms depend not only on pH and ionic strength but also on the electrolytes there were in the dissolution medium. In calcium pectinate beads, rutin release was faster when phosphate buffers were used because precipitates (CaHPO4) were formed. This precipitate has a pumping effect on the calcium ions, destabilizing the gel structure and enhancing rutin release. In the case of zinc pectinate beads, two kinds of precipitate can be developed depending on the electrolytes composition. The development of Zn3(PO4)2 with a coating property reduced rutin release (Sorensen's buffer). On the other hand, development of ZnHPO4 has the pumping effect of zinc ions coming from the beads which increased rutin release (Mc Ilvaine's buffer).