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 E udragit, 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, whic h result from the cross-linking reaction between pectin and calcium ion. Th e beads were freeze-dried to obtain spherical particles, which were then co ated with Eudragit S100 in an aqueous phase using a fluidised-bed spray coa ter. The release profile of the drug was measured in two solutions, both de signed to mimic the environment in the human intestine. These are a phospha te buffer, frequently used for this purpose (but which may have the drawbac k of a possible interaction between the basic ions and the coating material ), and a physiological salt solution (Hank's pH 7.4), which resembles the p H and ion concentration in the fluid of the small intestine. From the resul ts obtained, it was found that the drug release rate in the phosphate buffe r was significantly faster than that in Hank's solution. This effect was ev en more pronounced when the coating thickness was increased. The comparison of the drug release profile between the two dissolution liquids is made, a nd the feasibility of using the Eudragit S capsules to deliver the drug to the colon is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.