Swelling of pellets coated with a composite film containing ethyl cellulose and hydroxypropyl methylcellulose

The swelling behaviour of membrane-coated drug pellets has been investigated. A coating membrane containing ethyl cellulose (EC) and hydroxypropyl methylcellulose (HPMC) in the range of 10-24% was used. By measuring the release rate of a drug during swelling experiments, it is possible to obtain an insight into the release mechanisms that are involved. The results revealed that the swelling of the membrane coat increased as the amount of HPMC increased. The expansion of the pellets continued until the release of the drug began. We have also evaluated the swelling of pure EC/HPMC, where no change in volume occurred. It is believed that the swelling of the pellet coat is a result of water imbibition due to osmotic pressure. (C) 1998 Elsevier Science B.V.