Comparison of the release profiles of a water soluble drug carried by Eudragit-coated capsules in different in-vitro dissolution liquids

Methylacrylic acid–methylmethacrylate copolymers, which are also known as Eudragit, have been used as a pH sensitive coating material to protect drug substances prior to delivery to the human intestines. A water soluble model drug, theophylline, was immobilized in calcium pectinate (CaP) beads, which result from the cross-linking reaction between pectin and calcium ion. The beads were freeze-dried to obtain spherical particles, which were then coated with Eudragit S100 in an aqueous phase using a fluidised-bed spray coater. The release profile of the drug was measured in two solutions, both designed to mimic the environment in the human intestine. These are a phosphate buffer, frequently used for this purpose (but which may have the drawback of a possible interaction between the basic ions and the coating material), and a physiological salt solution (Hankʹs pH 7.4), which resembles the pH and ion concentration in the fluid of the small intestine. From the results obtained, it was found that the drug release rate in the phosphate buffer was significantly faster than that in Hankʹs solution. This effect was even more pronounced when the coating thickness was increased. The comparison of the drug release profile between the two dissolution liquids is made, and the feasibility of using the Eudragit S capsules to deliver the drug to the colon is discussed.